Base by Base

Gustavo Barra
  • 3.0 (2)
  • Life Sciences
  • Daily

Base by Base explores advances in genetics and genomics, with a focus on gene-disease associations, variant interpretation, protein structure, and insights from exome and genome sequencing. Each episode breaks down key studies and their clinical relevance—one base at a time. Powered by AI, Base by Base offers a new way to learn on the go. Special thanks to authors who publish under CC BY 4.0, making open-access science faster to share and easier to explore.

  1. 22h ago

    472: 490,319 genomes that fill the gaps in genetic studies

    Wienbrandt L et al., Nature Genetics - Most genetic studies read only a fraction of the genome and infer the rest from a reference panel. This episode covers a new panel built from whole-genome sequencing of 490,319 UK Biobank participants, benchmarked against the TOPMed r3 panel across 35 datasets and used to reanalyze COVID-19 association studies from four European countries. Key terms: genotype imputation, haplotype reference panel, UK Biobank, EagleImp, COVID-19 GWAS. Study Highlights: Researchers phased whole-genome data from 490,319 UK Biobank participants into reference panels of more than 361 million variants and extended EagleImp to run on a standalone server and inside the UK Biobank Research Analysis Platform. Compared with the TOPMed r3 panel of 133,597 individuals, the UK Biobank panel achieved lower phasing switch error rates for all superpopulations except AMR and for 25 of 26 1000 Genomes subpopulations. Mean absolute error improved for 4 of 5 superpopulations and 12 subpopulations, while TOPMed performed better across all frequency categories in AFR. Estimated R2 improved across all 5 superpopulations and 22 subpopulations for variants down to 0.01% frequency, with the largest gain, +24.39%, in East Asian samples. Reimputing an Italian severe COVID-19 study of 835 cases and 1,255 controls yielded a genome-wide significant association at 3p21.31 and a new lead SNP, rs73064425, that matched three independent studies. Conclusion: The authors conclude that the UK Biobank panel is the most suitable panel for imputing worldwide populations when no population-specific panel is available, and that common-variant imputation is not yet saturated in the European populations tested. The benchmark has limits: estimated imputation R2 stays low for most subpopulations below 0.01% frequency, truth-based measures may be inaccurate at low frequencies, and TOPMed r3 still performed better in AFR on mean absolute error and holds more panel-specific variants. Article title: A haplotype reference panel constructed from 490,319 UK Biobank genomes improves genotype imputation for global populations First author: Wienbrandt L Journal: Nature Genetics DOI: 10.1038/s41588-026-02819-0 Reference: Wienbrandt L., Prieß C., Schmöhl M., Neff V., Gretsova M., Torres G., et al. A haplotype reference panel constructed from 490,319 UK Biobank genomes improves genotype imputation for global populations. Nature Genetics. (2026). https://doi.org/10.1038/s41588-026-02819-0 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/uk-biobank-haplotype-reference-panel-imputation QC: This episode's script was checked sentence by sentence against the full text of the original article, by an automated process with human review, before it was recorded. QC Summary: - sentences checked: 176 - supported by the article: 143 - flagged and reviewed by a human: 33 - metadata checks passed: 4 of 4 QC result: Warn. Chapters (00:00:03) - The Restorer Analogy: Imputation Explained(00:01:03) - Genotyping Chips and the Need for Imputation(00:02:16) - Introducing the Study and Its Authors(00:02:55) - What Haplotypes Are and How Imputation Works(00:03:44) - Limits of Existing Panels: Access and Scale(00:04:37) - Is Imputation Already Saturated?(00:05:20) - Building the UK Biobank Panel(00:06:38) - Creating the Lighter Panel and Software Tools(00:07:11) - Designing the Benchmark(00:08:39) - Phasing Results: UK Biobank vs TopMed(00:09:49) - Checking Against Known Truth: Mixed Results(00:10:38) - Testing on Real GWAS Datasets(00:11:14) - Speed and Efficiency Gains(00:11:52) - The Italian COVID-19 Case Study(00:13:12) - Fine-Mapping the Causal Variant(00:13:53) - Revisiting the Saturation Question(00:14:58) - Limitations of the Study(00:15:35) - Remaining Gaps and Future Directions(00:16:12) - Conclusion: What the Bigger Archive Reveals

  2. 3d ago

    471: How cancer treatment picks winners among mutant clones in the normal esophagus

    Fowler J et al., Nature Genetics - Normal esophageal lining is a patchwork of mutant clones that compete for space as we age. This study asked whether cancer treatment changes which of those clones win. Normal esophagus removed at surgery from 70 patients with esophageal cancer, who had received no treatment, combination chemotherapy (ECX, EOX or FLOT) or chemoradiation (CROSS), was analyzed with duplex (NanoSeq), whole-genome and targeted sequencing, alongside protein structure modeling and a CRISPR experiment in mouse esophageal cultures. Key terms: somatic mutation, clonal selection, esophagus, chemoradiation, TP53. Study Highlights: Targeted sequencing of 1,995 samples of 2 mm2 across 324 cancer-associated genes found 23,692 independent mutations, and no chemotherapy mutational signature was detected, suggesting most clones existed before treatment. In patients given CROSS, the proportion of epithelium mutant for TP53 and PPM1D was double that of the other groups, their mutational burden and deletion burden were higher, and over 5% of samples carried a copy number event covering the TP53 locus. HLA-B and SPOP mutants were selected only in CROSS patients, with 13 of 22 HLA-B nonsynonymous mutations predicted to abolish the protein. RAC1, NFE2L2 and MTOR mutants were under positive selection only in the FLOT group, the only regimen giving 5-fluorouracil together with leucovorin, and structural modeling suggested the MTOR mutants would likely remain sensitive to rapalogs. In mouse esophageal cultures, guide RNAs targeting exon 6 of Ppm1d were enriched after irradiation but not after 5-fluorouracil. Conclusion: Weeks of neoadjuvant treatment can reshape a mutational landscape built over decades, selectively expanding preexisting mutant clones in a treatment-specific way, which may point to genes involved in cellular resilience to therapy. The groups were small (FLOT had seven patients), exposure data were limited, the mouse experiment did not test the full CROSS combination, the selection of MTOR, RAC1 and NFE2L2 mutants by 5-fluorouracil is inferred rather than tested, and selection in normal tissue cannot be assumed to match selection in cancer cells. Article title: Cancer treatment alters mutant selection in normal esophagus First author: Fowler J Journal: Nature Genetics DOI: 10.1038/s41588-026-02738-0 Reference: Fowler J.C., Arbore G., Sood R.K., Abnizova I., Albarello L., Pickering O., et al. Cancer treatment alters mutant selection in normal esophagus. Nature Genetics, 58, 2566-2578. (2026). https://doi.org/10.1038/s41588-026-02738-0 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/cancer-treatment-mutant-selection-normal-esophagus QC: This episode's script was checked sentence by sentence against the full text of the original article, by an automated process with human review, before it was recorded. QC Summary: - sentences checked: 171 - supported by the article: 167 - flagged and reviewed by a human: 4 - metadata checks passed: 4 of 4 QC result: Pass. Chapters (00:00:03) - The Forest Fire Analogy: Introduction(00:00:37) - Introducing Base by Base and the Paper(00:00:58) - Mutant Clones in the Aging Esophagus(00:01:29) - The Research Question and Team(00:02:21) - Treatment Regimens: Chemotherapy and CROSS(00:03:04) - The Study Opportunity at Surgery(00:03:44) - Mutational Signatures Explained(00:04:23) - Patient Cohort and Tissue Sampling(00:05:07) - Sequencing Methods: Mapping the Clones(00:06:16) - Measuring Selection in Genes(00:06:49) - Protein Structure Modeling and Lab Tests(00:07:23) - No Treatment-Specific Mutational Signature Found(00:07:50) - CROSS Group Stands Out: Mutation Load(00:09:01) - PPM1D Mutations and Radiation Resistance(00:10:07) - Chromosome 17 and TP53 Disruption in CROSS(00:10:41) - HLA-B and SPOP Selection in CROSS Patients(00:11:15) - FLOT-Selected Genes: NFE2L2, RAC1, MTOR(00:12:25) - RAC1 and MTOR Mechanisms in FLOT(00:13:44) - Interpreting the Findings: Speed of Change(00:14:16) - Why TP53 Results Matter for Cancer Risk(00:14:57) - The FLOT Question: Resistance Implications(00:15:34) - Study Limitations(00:16:12) - Summary: Different Fires, Different Winners(00:16:50) - Closing Thoughts and Credits

  3. 5d ago

    470: The hidden swaps CRISPR leaves between sister chromosomes

    Chovanec P et al., eLife - When CRISPR/Cas9 cuts DNA, editing is usually judged by the small insertions and deletions left at the break. But a cut can also be repaired by swapping DNA between the two identical sister chromatids, an exchange that leaves no sequence change and is invisible to standard sequencing. Using sci-L3-Strand-seq, a single-cell method that reads which parental template strand each daughter cell inherited, this study mapped Cas9-induced sister chromatid exchange (SCE) in human cells, after cutting either one unique site or 237 repetitive Alu sites at once. Key terms: CRISPR/Cas9, sister chromatid exchange, Strand-seq, DNA double-strand break repair, structural variants. Study Highlights: Duplex Cas9 cleavage at a single site or at 237 repetitive targets caused a pronounced G1/S arrest within 24 hr, while the D10A and H840A nickases did not measurably perturb cell-cycle progression after washout. Cutting a unique locus strongly enriched SCE at the break site, reaching 41% in the same cell cycle and 17% in the subsequent division. Across all cells, cutting 237 Alu sites gave only mild on-target enrichment, 1.20-fold in the post-washout condition (n=2547 cells), but a high-SCE subset of 261 cells showed 1.39-fold enrichment with an average of 14.61 on-target SCEs per cell. Reciprocal daughter-cell pair analysis found that 14 of 50 Cas9-induced SCE events were coupled with structural variants, in contrast to 87 of 87 spontaneous SCEs in XRCC1-null cells that were reciprocal and copy-neutral in a companion study. Cutting inside LIG3, LIG4, XRCC1 and XRCC4 did not change genome-wide SCE counts, with a median of three SCEs per cell in all four conditions, consistent with delayed functional loss after editing. Conclusion: Cas9-induced double-strand breaks are potent local triggers of sister chromatid exchange, and a measurable fraction of these exchanges carries structural alterations that conventional sequencing cannot see, so they do not universally reflect error-free homologous recombination. All experiments were done in wild-type cells, Cas9 can cut the same site several times so individual outcomes cannot be tied to a single cleavage event, and the deletion signature pointing to a TRAIP/under-replicated-region pathway rests on a single daughter-cell pair. Article title: Genome-wide mapping of Cas9-induced sister chromatid exchange across single and over 200 genomic sites in human cells First author: Chovanec P Journal: eLife DOI: 10.7554/eLife.112073 Reference: Chovanec P., He S., Yin Y. Genome-wide mapping of Cas9-induced sister chromatid exchange across single and over 200 genomic sites in human cells. eLife, 15. (2026). https://doi.org/10.7554/eLife.112073 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/cas9-sister-chromatid-exchange-strand-seq QC: This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-10-29. QC Scope: - article metadata and core scientific claims from the narration - excludes analogies, intro/outro, and music - transcript... Chapters (00:00:03) - The Deck of Cards Analogy(00:00:41) - Intro and Fact-Check Note(00:01:02) - Sister Chromatids and Silent Swaps(00:01:33) - Cas9 Scissors and Hidden Repairs(00:02:08) - Paper Introduction(00:02:44) - How Cas9 Cuts Are Normally Repaired(00:03:24) - Bigger Damage Beyond Small Edits(00:03:57) - Defining Sister Chromatid Exchange(00:04:17) - Four Broken Ends and Open Questions(00:05:28) - Strand-Seq: Reading the Backs of the Cards(00:06:37) - Experimental Design and Guides(00:07:46) - Cell Cycle Arrest Findings(00:08:22) - Exchanges Pile Up at the Cut Site(00:08:53) - Interpreting the 41% Exchange Rate(00:10:02) - Checking Repair Gene Targets(00:10:34) - Cutting 237 Sites at Once(00:11:11) - High-Exchange Cell Subsets(00:12:22) - Reciprocal Daughter Pairs and Clean Trades(00:12:53) - When Trades Aren't Clean(00:13:24) - Rethinking How We Judge Edits(00:14:00) - Isochromatid Breaks and Mechanism(00:14:59) - Caveats on Causation and Single Observations(00:15:55) - Conclusions and Implications(00:16:51) - Closing and Credits

  4. 6d ago

    469: What the shape of a face reveals about cleft risk

    Herrick N et al., Human Genetics and Genomics Advances - Orofacial clefts are among the most common birth defects, affecting about 1 in 700 births, yet known genetic signals explain only a fraction of their heritability, and cleft studies cannot reach the huge sample sizes used for traits like height. This study borrowed statistical power from a related trait: the genetics of normal human face shape. Using a pleiotropy-informed method called conditional false discovery rate, the team re-analyzed an existing GWAS of nonsyndromic cleft lip with or without cleft palate and found new candidate risk loci, three of which passed a 5% FDR threshold in an independent replication cohort. Key terms: orofacial cleft, facial shape, GWAS, conditional false discovery rate, pleiotropy. Study Highlights: The team conditioned summary statistics from a European nsCL/P GWAS of 3,969 individuals on two independent facial shape GWASs, from 4,680 US and 3,566 UK individuals. SNPs associated with nsCL/P were enriched among SNPs associated with facial shape but not among those for unrelated traits such as height, schizophrenia or LDL cholesterol. The cFDR approach identified 21 independent loci at a 5% threshold and 15 more at 10%, and the new loci had effect sizes comparable to known ones, with no significant difference in a Mann-Whitney U test (p = 0.26). Of 13 new lead SNPs tested in The Cleft Collective cohort of 1,084 affected individuals and 7,913 controls, five replicated at p 0.05, and loci near MSX2, ASPSCR1 and FHOD3 passed a 5% FDR threshold. Spatial transcriptomics of a Carnegie stage 13 human embryo showed expression and gene specificity scores for these genes in the pharyngeal arches, among other regions. Conclusion: Leveraging the shared genetics of face shape and clefting can recover cleft risk loci that a standard GWAS of the same data misses, and it supports the long-standing idea that embryonic face shape is itself part of cleft risk. The analysis is limited to people of European ancestry, the authors expect about 10% of the 36 loci to be false positives, not every new locus replicated, and the expression data support but do not prove a role for the candidate genes. Article title: Leveraging the genetics of human face shape boosts the discovery of orofacial cleft risk loci First author: Herrick N Journal: Human Genetics and Genomics Advances DOI: 10.1016/j.xhgg.2026.100655 Reference: Herrick N., Goovaerts S., Manchel A., Lee M.K., Zhang X., Davies A., et al. Leveraging the genetics of human face shape boosts the discovery of orofacial cleft risk loci. Human Genetics and Genomics Advances, 7, 100655. (2026). https://doi.org/10.1016/j.xhgg.2026.100655 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/face-shape-genetics-orofacial-cleft-risk-loci QC: This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-10-27. QC Scope: - article metadata and core scientific claims from the narration - excludes analogies, intro/outro, and music - transcript coverage: All scientific... Chapters (00:00:03) - Introduction: Face Shape and Clefts(00:01:21) - The Study and Researchers(00:02:18) - Background on Orofacial Clefts(00:03:28) - The Face-Cleft Genetic Link Hypothesis(00:04:46) - The CFDR Method Explained(00:05:21) - Study Data and Controls(00:07:01) - Analysis Details and Validation Approach(00:07:41) - Results: Face Shape as a Predictive Map(00:08:17) - Main Findings: New Cleft Loci Discovered(00:08:49) - Comparing US and UK Cohorts(00:09:23) - Are New Loci Real? Effect Size Check(00:09:56) - Replication in the Cleft Collective Cohort(00:11:06) - Regional Plots of Three Candidate Genes(00:11:36) - Gene Expression in the Embryo(00:12:41) - Spatial Genetic Risk Mapping (GSMap)(00:13:17) - MSX2: A Known Suspect Confirmed(00:13:53) - ASPSCR1 and FHOD3: New Biological Clues(00:15:05) - Bigger Picture: Shared Genetic Architecture(00:16:10) - Limitations of the Study(00:16:48) - Conclusions and Closing Thoughts

  5. Oct 25

    468: When a splicing factor breaks in different ways

    Lisfeld J et al., The American Journal of Human Genetics - SRSF3 is an essential splicing factor, one of the serine/arginine-rich proteins that help cells cut and paste their RNA messages and send them out of the nucleus. Losing it completely is lethal in mouse embryos. This study describes nine individuals with new, non-inherited SRSF3 variants and variable developmental phenotypes, with developmental delay and/or mild to moderate intellectual disability as the most consistent feature. Functional experiments in patient fibroblasts and human cell lines showed that each variant damaged the protein in a different combination of ways, which may help explain why affected individuals differ so much. Key terms: SRSF3, splicing, de novo variants, neurodevelopmental disorder, spliceosomopathy. Study Highlights: Through GeneMatcher, the team recruited nine subjects with six heterozygous de novo SRSF3 variants: two missense variants in the RNA recognition motif, three frameshifts and a recurrent nonsense variant, p.Arg149*, found in four unrelated subjects. In fibroblasts from subject 3, transcripts carrying the c.330_331del frameshift were largely degraded by nonsense-mediated decay, with only about 12.5% of SRSF3 reads carrying the deletion, yet overall SRSF3 mRNA and protein levels were normal, suggesting compensation from the other allele. In HEK293T cells, all five variant proteins tested formed less complex with polyadenylated RNA than wild type, while the three C-terminally truncated proteins were poorly phosphorylated, less stable, at about 46% to 59% of wild-type levels, and showed reduced nucleocytoplasmic shuttling in HeLa cells. Complex formation with the export factors YTHDC1 and NXF1 was reduced for p.Arg137Ilefs*16 and p.Arg149* and increased for p.Ser81Trp. Conclusion: De novo SRSF3 variants define a new spliceosomopathy with a broad developmental spectrum, and the variants appear to act through distinct mechanisms rather than simple loss of half the protein. The cohort is small, most functional work used overexpressed proteins in cell lines rather than affected tissues, the evidence against haploinsufficiency comes from one subject and one cell type, and the c.330_331del variant remains of uncertain significance. Article title: De novo variants in the essential splicing factor gene SRSF3 cause variable developmental phenotypes First author: Lisfeld J Journal: The American Journal of Human Genetics DOI: 10.1016/j.ajhg.2026.09.018 Reference: Lisfeld J., Chinn I.K., Yuan B., Casar C., Müller C., Elron E., et al. De novo variants in the essential splicing factor gene SRSF3 cause variable developmental phenotypes. The American Journal of Human Genetics. (2026). https://doi.org/10.1016/j.ajhg.2026.09.018 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/srsf3-de-novo-variants-splicing-factor-development QC: This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-10-25. QC Scope: - article metadata and core scientific claims from the narration - excludes analogies, in... Chapters (00:00:03) - Introduction: Nine Children, One Gene(00:01:03) - The Film Editor Analogy(00:01:42) - Study Credits and Paper Overview(00:02:23) - Understanding Splicing and the Spliceosome(00:02:57) - SR Proteins and SRSF3 Basics(00:03:29) - SRSF3 Structure and Phosphorylation Cycle(00:04:41) - SRSF3's Self-Regulating Poison Exon(00:05:18) - Finding the Children via GeneMatcher(00:05:55) - Types of Variants Found(00:06:30) - Lab Methods: Testing the Variants(00:07:05) - Control Variants for Validation(00:07:33) - Clinical Features of the Children(00:08:02) - Variability Within the Same Variant(00:08:44) - Subject 3: A Surprising Compensation(00:09:16) - Confirming Normal Protein Levels in Subject 3(00:09:48) - Interpreting Subject 3's Uncertain Variant(00:10:20) - Tail Tagging Experiments(00:11:19) - Protein Stability and Tag Protection(00:11:28) - RNA Gripping Deficits Across Variants(00:11:50) - Nuclear Shuttling Defects(00:12:36) - Export Partner Binding Differences(00:13:06) - Each Variant's Unique Defect Combination(00:13:44) - SRSF3 as a New Spliceosomopathy(00:14:18) - Comparison to SRSF1 and Clinical Implications(00:14:52) - Challenging Assumptions About Truncating Variants(00:15:24) - Study Limitations(00:16:02) - Summary: One Gene, Many Breaks(00:16:35) - Closing and Credits

  6. Oct 18

    467: Finding mutations carried by fewer than 1 in 100 cells

    Jang Y et al., The American Journal of Human Genetics - Every cell in the body picks up its own small set of DNA changes over a lifetime, and many of these somatic mutations are carried by only a tiny fraction of cells. This study, part of the SMaHT Network, asks how reliably standard bulk whole-genome sequencing can find mutations present at a variant allele fraction below 1%. The team built a ground truth from one donor's skin: clonal stem cell lines grown from single fibroblasts defined real mutations, and lines from other skin biopsies of the same donor defined mutations that should be absent. With about 1,360× Illumina coverage confirmed by PacBio and AVITI, point mutations below 1% were detected accurately in the easily mapped parts of the genome. Key terms: somatic mosaicism, whole-genome sequencing, variant allele fraction, benchmarking, SMaHT. Study Highlights: Primary fibroblasts from a 29-year-old donor contained five subclones, captured as clonal iPSC lines, giving benchmark mutations from 0.1% to 25% variant allele fraction, while iPSC lines from other biopsies of the same donor supplied negative controls; both sets held about 11,000 SNVs and 2,800 indels. Using the negative controls, PacBio and AVITI had the lowest substitution error rates in easy regions, 0.003% and 0.005%, and mismatch rates rose by 1 to 2 orders of magnitude in harder regions. In fibroblasts, more than 99.5% of bulk-only calls above 1% were confirmed by PacBio or AVITI, the estimated false-positive rate was near zero above 0.8% and about 11% below 0.5%, and homopolymer indels could be detected reliably only above 3%. In postmortem lung and colon, combining about 200× from two tissues found 13 additional shared mutations, a 145% gain in sensitivity below 3%, all confirmed by PacBio or single-cell data. Conclusion: Ultra-deep bulk whole-genome sequencing can detect point mutations below 1% allele fraction with high accuracy, provided calling is restricted to easily mapped regions and sample quality is checked, and pooling coverage across tissues from one donor recovers shared developmental mutations. The benchmark comes from a single donor's fibroblasts, confirmation below 0.5% was limited by long-read and AVITI coverage, most indels sit in homopolymers or hard regions where detection remains unreliable, and postmortem samples needed extra filtering. Article title: Accurate detection of sub-1% frequency somatic mutations by whole-genome sequencing First author: Jang Y Journal: The American Journal of Human Genetics DOI: 10.1016/j.ajhg.2026.09.010 Reference: Jang Y., Gardiner S., Wang Y., Natu A., Dehankar M.K., Tomasini L., et al. Accurate detection of sub-1% frequency somatic mutations by whole-genome sequencing. The American Journal of Human Genetics. (2026). https://doi.org/10.1016/j.ajhg.2026.09.010 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/detecting-sub-1-percent-somatic-mutations-wgs QC: This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-10-18. QC Scope: - article metadata...

  7. Oct 16

    466: A quieter MECP2 switch and the male bias in autism

    Meyer-Schuman R et al., The American Journal of Human Genetics - Autism is diagnosed about four times more often in male individuals than in female individuals, and one explanation is mild variants in dosage-sensitive genes on the X chromosome, which a female carrier can buffer with her second copy but a male cannot. This study tests that idea in MECP2, the Rett syndrome gene, by looking at the switches that control how much of it is made rather than the gene itself. Using a massively parallel reporter assay in human stem-cell-derived neurons, the team mapped the active transcription factor binding sites in five MECP2 regulatory elements and tested 22 ultra-rare variants passed from unaffected mothers to autistic sons. Two variants changed regulatory activity, and one in the promoter lowered MECP2 RNA and protein by about 30% when edited into the native gene. Key terms: MECP2, autism, massively parallel reporter assay, noncoding variants, X chromosome. Study Highlights: Whole-genome data from 30,916 individuals in 8,245 autism families yielded 22 ultra-rare noncoding variants in MECP2 regulatory elements, each private to one family, found only in male probands and inherited from an unaffected mother, tested alongside 19 gnomAD control variants. Shuffling predicted transcription factor motifs mapped activator or repressor hotspots in four of the five elements, and knocking down two predicted activators, TCF3 and ZNF281, lowered MECP2 RNA by about 55% and 47% after three weeks. A variant in the primate-specific repressor element CRE A, carried by two affected brothers, increased activity in both the reporter and luciferase assays. The promoter variant g.154097837A>G, found in a boy with autism and ADHD and a full-scale IQ of 97, weakened NFY-B binding at the MECP2 promoter from the 51st to the 9th percentile of bound promoters and reduced MECP2 RNA and protein by about 30% in edited neurons. Conclusion: The findings suggest that noncoding MECP2 variants that modestly lower or raise expression can contribute to idiopathic, male-biased autism, and they provide a framework for finding regulatory variants in other X chromosome neurodevelopmental genes. The evidence rests on two families and on reporter assays and edited neurons in a dish, which take short sequences out of their native chromatin context, so the link between these variants and autism still needs additional variant discoveries and molecular validation. Article title: A massively parallel reporter assay of MECP2 cis-regulatory elements reveals genetic candidates for male-biased autism First author: Meyer-Schuman R Journal: The American Journal of Human Genetics DOI: 10.1016/j.ajhg.2026.09.011 Reference: Meyer-Schuman R., Cherry F., Sui Y., Papastathopoulos-Katsaros A., Zhong Y., Li Y., et al. A massively parallel reporter assay of MECP2 cis-regulatory elements reveals genetic candidates for male-biased autism. The American Journal of Human Genetics. (2026). https://doi.org/10.1016/j.ajhg.2026.09.011 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/mecp2-regulatory-variants-male-biased-autism QC:... Chapters (00:00:20) - Introduction: A Family Mystery(00:01:19) - The X Chromosome and Autism's Male Bias(00:01:45) - The Dimmer Switch Analogy(00:02:35) - Introducing the Study and Authors(00:03:13) - MECP2 Gene and Dose Sensitivity(00:04:27) - Mouse Evidence for Narrow Safe Range(00:05:33) - The Broader X-Linked Puzzle(00:06:10) - Finding Candidate Regulatory Elements(00:06:45) - Selecting Variants from Families(00:07:20) - Massively Parallel Reporter Assay Explained(00:08:30) - Testing in Human Neurons(00:08:56) - Mapping Hotspots Across Elements(00:09:50) - Identifying Transcription Factors(00:10:27) - Switch Teamwork and Context Dependence(00:10:57) - Element A Variant in Two Brothers(00:12:14) - Promoter Variants and Luciferase Testing(00:12:48) - The Boy with the Promoter Variant(00:13:22) - CRISPR Validation of NFY Binding Loss(00:14:18) - Measuring the Downstream Effects(00:14:57) - What the Findings Add Up To(00:15:32) - Why Mild Cases Survive the Filter(00:16:03) - Beyond MECP2: Broader Implications(00:16:33) - Study Limitations(00:17:15) - Conclusion: Quiet Switches and the Future(00:18:13) - Closing and Credits

  8. Oct 11

    465: When a lysosomal storage gene shows up only in the retina

    Lin et al., The American Journal of Human Genetics - Bi-allelic variants in IDUA classically cause mucopolysaccharidosis type I, a lysosomal storage disorder that affects many organs from childhood. This study describes 14 adults and young adults from 12 families who first came to eye clinics with retinitis pigmentosa and were later found to carry bi-allelic IDUA variants. Seven of them showed no systemic features of the disease even after detailed assessment, and enzyme activity in white blood cells was reduced but never absent. Cell-based enzyme assays and long-read RNA sequencing explain how mild, hypomorphic alleles can leave just enough enzyme to spare the body but not the retina. Key terms: IDUA, mucopolysaccharidosis type I, retinitis pigmentosa, hypomorphic variants, splicing. Study Highlights: Individuals aged 19 to 73 were recruited from inherited retinal disease cohorts in the UK, Ireland, Italy, the Netherlands and the United States, and none carried two null alleles; most had a loss-of-function allele paired with a missense variant. Leukocyte alpha-L-iduronidase activity was reduced but detectable in all nine individuals tested, and urine glycosaminoglycans were above normal in only half of those tested, with modest elevations. In an IDUA-knockout cell line, several missense variants, including p.His91Tyr and p.Arg383His, showed relative specific activity around 0.5% to 1.5% of wild type, with poor processing or stability. The recurrent c.298A>G variant left enzyme activity intact as a protein change, but nanopore long-read sequencing showed that it mostly causes exon 2 skipping, with only about 1.3% of reads from that allele spliced normally. Conclusion: Hypomorphic IDUA genotypes that leave low residual enzyme activity can cause late-onset retinitis pigmentosa with mild or apparently no systemic disease, extending the known spectrum of MPS I and arguing for including IDUA in inherited retinal disease gene panels. The cohort is small and mostly of European ancestry, systemic assessment varied in depth, and without longitudinal follow-up some individuals classed as having isolated retinal disease may still develop systemic features. Article title: Hypomorphic IDUA genotypes are associated with retinitis pigmentosa in individuals without syndromic mucopolysaccharidosis type I First author: Lin Journal: The American Journal of Human Genetics DOI: 10.1016/j.ajhg.2026.09.008 Reference: Lin, S., Yu, S.-H., Browning, A. C., et al., Roosing, S., Steet, R., and Arno, G. (2026). Hypomorphic IDUA genotypes are associated with retinitis pigmentosa in individuals without syndromic mucopolysaccharidosis type I. The American Journal of Human Genetics 113, 1-12. https://doi.org/10.1016/j.ajhg.2026.09.008 License: This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/ Support: Base by Base is independent and ad-free — no sponsors, no paywall. If an episode was worth your time, chip in and keep the papers audited and the original songs coming: ❤️ Support monthly: https://buy.stripe.com/cNifZhclVebvagk2JDgEg01 ☕ One-time donation: https://donate.stripe.com/7sY4gz71B2sN3RWac5gEg00 ▶️ Watch with chapters on YouTube: https://www.youtube.com/@basebybase More at basebybase.com On PaperCast Base by Base you'll discover the latest in genomics, functional genomics, structural genomics, and proteomics. Episode link: https://basebybase.com/episodes/idua-hypomorphic-retinitis-pigmentosa-mps-i QC: This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-10-11. QC Scope: - article metadata and core scientific claims from the narration - excludes analogies, intro/out... Chapters (00:00:20) - Introduction: Two Faces of One Gene(00:01:54) - The Lysosome Crew Analogy(00:03:01) - Study Overview and Authors(00:03:44) - Understanding IDUA and MPS1(00:04:23) - MPS1 Severity Spectrum and Eye Involvement(00:05:41) - The Unclear Case of Retina-Only Disease(00:06:54) - Study Cohort and Methods(00:08:06) - Clinical Eye Workup and Testing(00:08:38) - Measuring Enzyme Activity in the Lab(00:09:44) - RNA Sequencing of a Puzzling Variant(00:10:18) - Genetic Findings: One Null, One Missense(00:10:49) - Clinical Results: Retina Affected, Body Spared(00:12:01) - Biochemical Results: Reduced but Not Absent(00:12:37) - Variant-by-Variant Activity Results(00:13:50) - The Recurrent Splicing Variant Mystery(00:14:26) - Long-Read Sequencing Reveals Leaky Splicing(00:15:37) - Why the Retina Fails First(00:16:15) - Clinical Implications for Diagnosis and Panels(00:16:51) - Therapeutic Implications(00:17:18) - Newborn Screening Dilemma(00:17:55) - Study Limitations(00:18:31) - Conclusions and Open Questions(00:19:31) - Closing and Credits

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About

Base by Base explores advances in genetics and genomics, with a focus on gene-disease associations, variant interpretation, protein structure, and insights from exome and genome sequencing. Each episode breaks down key studies and their clinical relevance—one base at a time. Powered by AI, Base by Base offers a new way to learn on the go. Special thanks to authors who publish under CC BY 4.0, making open-access science faster to share and easier to explore.

Information

  • Creator
    Gustavo Barra
  • Years Active
    2025 - 2026
  • Episodes
    473
  • Rating
    Clean
  • Copyright
    © Gustavo Barra
  • Show Website
    Base by Base

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