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Results for “bi-allelic”

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PubMed2025

Bi-allelic loss-of-function variants in POC5 cause a syndromic retinal, endocrine, and neuromuscular ciliopathy.

PURPOSE: A homozygous loss-of-function (LoF) variant in POC5 was previously described in an individual with retinitis pigmentosa. We identified POC5 variants in 12 probands with a syndromic phenotype. We aim to define the phenotype spectrum and molecular mechanism associated with biallelic POC5 LoF variants. METHODS: We studied a cohort of 12 families with bi-allelic LoF POC5 variants and performed detailed phenotype analysis. POC5 localization studies were performed in 3 proband-derived fibroblast cell lines. RESULTS: Detailed phenotyping of probands with POC5 variants expands the phenotype spectrum beyond ocular manifestations. This syndrome causes not only rod-cone dystrophy but also diabetes mellitus with severe insulin resistance and partial lipodystrophy, kidney disease, and muscle cramps. The POC5 protein plays an essential role during cell cycle and cilium formation. Interestingly, POC5 localization studies in 3 proband-derived fibroblast cell lines show aberrant localization suggesting a ciliary defect. The phenotypes of the 12 families in this study fit well within the ciliopathy phenotype spectrum, except for lipodystrophy, which is not common in ciliopathies. CONCLUSION: We describe a multiorgan syndrome caused by bi-allelic LoF variants in POC5. This underscores the pleiotropic effects of POC5 variants and highlights the significance of adipose tissue and metabolic dysfunction in ciliopathies.

Humans↗

PubMed2023

Bi-allelic ATG4D variants are associated with a neurodevelopmental disorder characterized by speech and motor impairment.

Autophagy regulates the degradation of damaged organelles and protein aggregates, and is critical for neuronal development, homeostasis, and maintenance, yet few neurodevelopmental disorders have been associated with pathogenic variants in genes encoding autophagy-related proteins. We report three individuals from two unrelated families with a neurodevelopmental disorder characterized by speech and motor impairment, and similar facial characteristics. Rare, conserved, bi-allelic variants were identified in ATG4D, encoding one of four ATG4 cysteine proteases important for autophagosome biogenesis, a hallmark of autophagy. Autophagosome biogenesis and induction of autophagy were intact in cells from affected individuals. However, studies evaluating the predominant substrate of ATG4D, GABARAPL1, demonstrated that three of the four ATG4D patient variants functionally impair ATG4D activity. GABARAPL1 is cleaved or "primed" by ATG4D and an in vitro GABARAPL1 priming assay revealed decreased priming activity for three of the four ATG4D variants. Furthermore, a rescue experiment performed in an ATG4 tetra knockout cell line, in which all four ATG4 isoforms were knocked out by gene editing, showed decreased GABARAPL1 priming activity for the two ATG4D missense variants located in the cysteine protease domain required for priming, suggesting that these variants impair the function of ATG4D. The clinical, bioinformatic, and functional data suggest that bi-allelic loss-of-function variants in ATG4D contribute to the pathogenesis of this syndromic neurodevelopmental disorder.

Journal Article↗

PubMed2026

Bi-allelic loss-of-function variants in JKAMP cause a neurodevelopmental syndrome associated with dysregulation of GPR37 trafficking.

The endoplasmic reticulum (ER) serves as a key hub for protein homeostasis, maintaining a strict quality-control system that ensures only properly folded proteins reach their destinations, while misfolded proteins are degraded via ER-associated degradation (ERAD) or selective ER-phagy. JKAMP, which encodes an ER-resident transmembrane protein involved in ERAD, has not previously been associated with human disease. Here, we report bi-allelic loss-of-function variants in JKAMP in 14 affected individuals from 10 unrelated families presenting with a neurodevelopmental syndrome characterized by intellectual disability, developmental delay, seizures, hypotonia, microcephaly, and dysmorphic features. An in vivo zebrafish model lacking jkamp recapitulated key aspects of the human disorder, including developmental abnormalities and impaired myelin production, further corroborating its pathogenic role. Mechanistic studies identified GPR37, a brain-enriched orphan G protein-coupled receptor (GPCR) and known JKAMP interactor, as a critical downstream effector. GPR37 plays essential roles in dopaminergic signaling, inflammatory pain regulation, neuroprotection, and myelination. Loss of JKAMP resulted in defective folding and degradation of GPR37, leading to its accumulation within the ER and impaired trafficking to the plasma membrane, likely due to impaired ER quality control. These findings establish JKAMP as a previously unrecognized contributor to human neurodevelopment and uncover a pathogenic mechanism linking ER protein quality control to GPCR regulation and neurological disease.

Humans↗

PubMed2026

AAV-mediated CBLN1 replacement rescues hereditary ataxia caused by bi-allelic CBLN1 variants.

Cbln1 is a secreted synaptic organizer required for parallel fiber-Purkinje cell (PF-PC) synapse integrity, climbing fiber (CF) refinement, and cerebellar motor learning but has not previously been implicated in human disease. We identified bi-allelic CBLN1 missense variants (A63P and Y112C) in two unrelated families with early-onset cerebellar ataxia accompanied by oculomotor abnormalities, cerebellar atrophy, and variable cognitive delay. In heterologous cells, both variants showed reduced steady-state protein abundance, impaired maturation through the early secretory pathway, and little or no detectable secretion, resulting in markedly reduced extracellular CBLN1 availability. Consistently, cerebellar granule cells expressing CBLN1-Y112C failed to induce excitatory synapses onto glutamate receptor δ2 (GluD2)-expressing cells in vitro. A knockin mouse harboring Y112C lacked synaptic Cbln1 and recapitulated key features of Cbln1 deficiency, including disrupted PF-PC synapse organization, persistent CF multi-innervation, impaired PF-PC transmission, and long-term depression, and deficits in motor coordination and oculomotor learning. Notably, systemic delivery of an astrocyte-targeted adeno-associated virus expressing wild-type CBLN1 in adult mutant mice restored synaptic CBLN1 localization, cerebellar synaptic function, plasticity, and behavior. These findings establish CBLN1 deficiency as a cause of hereditary ataxia and identify extracellular CBLN1 replacement as a therapeutic strategy for a reversible cerebellar synaptopathy.

CBLN1↗

PubMed2026

Heterozygous germline mutations in MSH3, and probably MLH3, act as classical tumour suppressors, leading to excess somatic deletion mutations, signature ID4 and increased colorectal cancer risk.

BACKGROUND: MSH3 and MLH3 are non-canonical DNA mismatch repair genes, involved in repairing insertion-deletion mutations. Colorectal cancer (CRC) and adenomas have been reported in patients with bi-allelic germline MSH3 mutations, and in a very few bi-allelic MLH3 mutation carriers. OBJECTIVES: We hypothesised that germline loss-of-function MSH3 and MLH3 mutations were akin to constitutional mismatch repair deficiency (cMMRd) and Lynch syndrome, such that CRC could result from either bi-allelic germline mutations or heterozygous germline mutations after second hits. DESIGN: About 12 000 CRC and multiple polyp cases and 460 000 controls were studied. 2023 patients underwent cancer genome sequencing. RESULTS: One CRC/multiple polyp case had bi-allelic MSH3 mutations and another, bi-allelic MLH3 mutations. MSH3 and MLH3 germline heterozygotes had an increased risk of CRC (2.2-fold, p=6.6×10-5 and 1.6-fold, p=0.028, respectively), owing to somatic 'second hits' that inactivated the wildtype allele. Single second hits sometimes inactivated both MSH3 and the nearby APC gene. All CRCs with MSH3 or MLH3 deficiency were microsatellite-stable but hypermutant. Deletions of ≥2 bp were particularly increased (~12-fold) and signature ID4 was usually present (p<0.0001). CRCs from heterozygotes without 'second hits' showed no hypermutation. CONCLUSION: The phenotypes of bi-allelic MSH3 and MLH3 mutation carriers resemble some patients with cMMRd. Heterozygous germline MSH3 and MLH3 alleles have incomplete penetrance, but increase CRC risk via hypermutation, phenotypically resembling PMS2-mutant Lynch syndrome. A causal association with specific mutations has not previously been reported for ID4 in human tumours. ID4 probably does not have a single aetiology, but can result from MSH3 or MLH3 deficiency.

COLONIC POLYPS↗

PubMed2026

B4GALT5 deficiency impairs glycosphingolipid biosynthesis: a new congenital disorder of glycosylation?

Lactosylceramide is a glycosphingolipid precursor synthesized by two dedicated galactosyltransferases, B4GALT5 and B4GALT6. The specific roles of B4GALT5 and B4GALT6 in humans have not yet been clearly defined. Here, we report the first human case with bi-allelic loss-of-function variants in B4GALT5, suggesting that intact B4GALT5 activity is indispensable for normal glycosphingolipid biosynthesis and human development. We identified bi-allelic variants in the B4GALT5 gene in a child presenting with microcephaly, mild cognitive impairment, and bilateral cataracts. B4GALT5/6 double KO cells transfected with B4GALT5 carrying either of the variants identified in the patient lacked lactosylceramide synthase activity and failed to produce glycosphingolipids. In silico analyses predicted decreased protein stability and impaired UDP-Gal binding for both B4GALT5 variants. Together, these findings indicate that both variants result in deficient B4GALT5 activity, leaving B4GALT6 as the sole source of lactosylceramide synthase activity. Consistent with this, patient plasma and fibroblasts exhibited an approximately 80% reduction in glycosphingolipid levels compared with healthy controls. Unexpectedly, when expressed in model cells human B4GALT6 displayed lower expression and lower catalytic activity, than human B4GALT5, raising questions about its capacity to compensate for B4GALT5 deficiency. In conclusion, we identified a potential new congenital disorder of glycosylation caused by deficient lactosylceramide synthase activity that may be insufficient to support glycosphingolipids synthesis at levels required for normal brain function.

Humans↗

PubMed2024

Exome-wide evidence of compound heterozygous effects across common phenotypes in the UK Biobank.

The phenotypic impact of compound heterozygous (CH) variation has not been investigated at the population scale. We phased rare variants (MAF ∼0.001%) in the UK Biobank (UKBB) exome-sequencing data to characterize recessive effects in 175,587 individuals across 311 common diseases. A total of 6.5% of individuals carry putatively damaging CH variants, 90% of which are only identifiable upon phasing rare variants (MAF < 0.38%). We identify six recessive gene-trait associations (p < 1.68 × 10-7) after accounting for relatedness, polygenicity, nearby common variants, and rare variant burden. Of these, just one is discovered when considering homozygosity alone. Using longitudinal health records, we additionally identify and replicate a novel association between bi-allelic variation in ATP2C2 and an earlier age at onset of chronic obstructive pulmonary disease (COPD) (p < 3.58 × 10-8). Genetic phase contributes to disease risk for gene-trait pairs: ATP2C2-COPD (p = 0.000238), FLG-asthma (p = 0.00205), and USH2A-visual impairment (p = 0.0084). We demonstrate the power of phasing large-scale genetic cohorts to discover phenome-wide consequences of compound heterozygosity.

Humans↗

PubMed2025

Male proband with intractable seizures and a de novo start-codon-disrupting variant in GLUL.

Bi-allelic variants in GLUL, encoding glutamine synthetase and responsible for the conversion of glutamate to glutamine, are associated with a severe recessive disease due to glutamine deficiency. A dominant disease mechanism was recently reported in nine females, all with a de novo single-nucleotide variant within the start codon or the 5' UTR of GLUL that truncates 17 amino acids of the protein product, including its critical N-terminal degron sequence. This truncation results in a disorder of abnormal glutamine synthetase stability and manifests as a phenotype of severe developmental and epileptic encephalopathy. Here, we report the first male with a pathogenic de novo variant in the same critical region of GLUL, with a phenotype of refractory focal and generalized seizures, as well as developmental delays. We provide a detailed description of the disease course and treatment response.

Humans↗

PubMed2026

Assessing the de novo paradigm in sporadic early-onset Alzheimer disease trios.

The genetic architecture of sporadic Early-Onset Alzheimer Disease (sEOAD, onset ≤65 years) remains largely unknown. To assess the de novo mutation (DNM) hypothesis, we performed a nationwide recruitment of 37 novel sEOAD patients-unaffected parents trios. After assessing known monogenic genes, we performed trio-based exome sequencing and jointly analyzed novel trios with 12 previously reported ones. Of these, we selected 16 trios for genome sequencing. We identified three patients with a pathogenic DNM in APP or PSEN1. Then, from the 46 remaining trios, we identified 38 non-synonymous coding DNM and 4 de novo copy number variants (CNVs) in exome data. Four DNM (2 novel, in SPHK2 and DDR1) and bi-allelic inherited variants in two genes affected Alzheimer disease-related genes. No significant burden of rare coding variants in exome/genome data from 5643 EOAD cases and 16097 controls was identified using nested windows centered on each DNM position, at the transcript level. From genome data, one non-coding DNM was predicted to affect splicing in an AD-associated gene, PINX1. Overall, 48% probands carried ≥1 inherited risk factor with odds ratio (OR) > 1.5 and GWAS-defined Genetic Risk Scores (GRS) distribution was more consistent with random distribution than enrichment in higher scores in probands. We confirm that DNMs in known monogenic genes explain sEOAD in a minority of cases, while candidate DNMs in other genes might account for a small proportion of additional cases. The majority of sEOAD patients may have a complex etiology including multiple inherited variants, however, GRS might not explain most of its genetic component.

Humans↗

PubMed2026

Generation of spCAS9 expressing human mesenchymal stem cell line to study gene function during osteoblast differentiation.

Human bone marrow-derived stromal cells (hMSCs) are a great resource for studying how genes influence cell fate and differentiation into various cell types like osteoblasts, adipocytes, and chondrocytes, among other cell types. However, genetic manipulation of primary hMSCs has been challenging due to their short lifespan and cellular senescence after limited passaging. Their low and unstable transfection efficiency also complicates gene delivery or inactivation, hindering long-term functional studies. The limited lifespan has been effectively solved by immortalizing hMSCs with telomerase reverse transcriptase (hMSCs-TERT). The use of these cells is ideal for functional studies of osteoblast and adipocyte differentiation through genetic manipulation, providing a stable and reliable model. Here, we have engineered a stable CAS9 expressing hMSC-TERT cell line (hMSC-TERTCAS9) via lentiviral transduction. The constitutive expression of spCas9 enables efficient and reproducible gene editing. We demonstrate the potential of these hMSC-TERTCAS9 cells for generating gene disruptions using plasmid delivery of guide RNAs as a fast and efficient strategy for targeted genome editing. The edited cells can be sorted and expanded as single cells to obtain homogenous clonal cell lines with mono- as well as bi-allelic gene deletions, a crucial step for producing reliable experimental results. We further validate this cell line as a powerful tool for studying gene function during hMSC proliferation and differentiation, providing 3 distinct examples of its utility. Through the generation of indels, single-cell sorting, and clonal selection, we have efficiently inactivated the vitamin D receptor and created both larger (256 nucleotides) gene disruptions in Forkhead box protein O1 and precise removals of a small genomic sequence (73 nucleotides) coding for microRNA MIR675. This novel hMSC-TERTCAS9 cell line represents a significant advancement, offering a stable, efficient, and versatile platform for advanced genetic studies, high-throughput screening, and the creation of reliable cellular disease models.

CRISPR-Cas9↗

PubMed2026

A CCNA1 Missense Variant Associated With Chromatid Non-Disjunction in Abnormal-Headed Sperm and Male Infertility.

BACKGROUND: Macrozoospermia is a rare form of teratozoospermia characterized by tetraploids, large-headed spermatozoa with multiple flagella, usually caused by bi-allelic AURKC mutations. The etiology of atypical phenotypes with a lower proportion of large headed spermatozoa and single flagella however often remains unresolved. OBJECTIVE: To investigate the genetic cause of severe sperm-head abnormalities with moderate macrozoospermia without multiflagellated spermatozoa in a patient with repeated ICSI failure. An infertile male with three failed ICSI attempts underwent semen analysis, revealing complete teratozoospermia, including 25% macrocephalic spermatozoa. METHODS: Multi-probe FISH targeting chromosomes 13, 18, 21, X, Y assessed chromosomal segregation. Whole-exome sequencing (WES) was performed to identify a candidate variant associated with meiotic abnormalities. RESULTS: FISH analysis revealed a high proportion of spermatozoa with n (23) chromosomes and 2c DNA content, consistent with sister chromatid non-disjunction during meiosis II. WES identified a homozygous missense variation in CCNA1, coding for a protein described to be essential for meiotic progression and chromatin remodeling in male germ cells. DISCUSSION: The variant affects a highly conserved residue within a functional domain and is predicted to be deleterious. This study establishes the first clinical association between CCNA1 mutations and chromatid non-disjunction in human spermatogenesis. It highlights the limitations of current morphology-based diagnostic thresholds and supports cytogenetic and genomic assessment for severe teratozoospermia (especially head abnormalities) and ART failure. CONCLUSION: Expanding genetic screening panels to include CCNA1 may improve diagnostic precision and clinical management in atypical macrozoospermia cases.

ART failure↗

PubMed2025

An In-Depth Review of the Genetics of the Non-Classical HLA Class I Gene HLA-E and Its Effects on Haematopoietic Cell Transplant Outcomes.

HLA-E is a non-classical HLA class I gene with limited reported genetic variability and few published studies into full-gene sequencing or population allele frequencies. Two protein variants, HLA-E*01:01 and HLA-E*01:03, are very common, accounting for 94%-100% of observed alleles in most studies performed to date. Frequently utilised exon-based sequencing strategies have led to the assumption of HLA-E being a near bi-allelic gene; however, recent full-gene sequencing studies have shown a greater degree of genetic variability than initially imagined. We carried out a literature review of HLA-E genotype and ethnicity data, which suggested HLA-E*01:03 is more common in Asian and, in particular, East Asian populations. Furthermore, HLA-E*01:03:02 is more frequently observed than HLA-E*01:03:01 in European and American populations, whereas HLA-E*01:03:01 is found at higher frequencies in Asian populations. It has been proposed that HLA-E may have a role in Haematopoietic Cell Transplantation (HCT) due to its interaction with NK and CD8+ T cells and its non-canonical peptide binding repertoire. Here we also review published literature into the effects of HLA-E genetics on HCT outcomes. Heterogeneity between cohorts muddies the waters; hence, studies report confounding effects of HLA-E genotype and matching on HCT outcomes. The need for further HLA-E sequencing of larger cohorts is evident to gain useful insight into the true genetic variability of HLA-E and its impact on HCT.

Humans↗

PubMed2026

Assessing Hardy-Weinberg equilibrium in T2T-aligned 1000 genomes project.

Quality control of markers in genome-wide association studies often includes testing for Hardy-Weinberg equilibrium (HWE). However, this is usually implemented in a homogeneous population without stratifying by sex. Previous work indicates sex-based selection at numerous autosomal loci in cohorts with active recruitment. Sex chromosome sequences can also interfere with autosomal SNPs. These motivate a re-examination of HWE in sex-aware analyses. Using the telomere-to-telomere (T2Tv2)-aligned high-coverage whole genome sequencing data from 2,490 individuals in the 1000 Genomes Project, we examined genome-wide sex-specific deviations from HWE across five super-populations. Our analyses were restricted to bi-allelic SNPs with non-missing genotypes and minor allele frequency (MAF) ≥5% in both sexes of the five super-populations. We applied an allele-based framework to quantify both the magnitude and direction of Hardy-Weinberg disequilibrium (HWD), followed by a second-order omnibus meta-analysis that combined HWD results across populations and sexes. At a genome-wide significance threshold of p < 5e-8, 0.9% of autosomal SNPs exhibited significant deviations from HWE. The majority of these deviations were associated with genomic features indicative of poor sequence quality. Restricting the analysis to reliable genomic regions substantially reduced the number of signals, yielding 255 autosomal SNPs and one non-pseudoautosomal chromosome X SNP. Among these, 140 autosomal SNPs displayed significant heterogeneity across populations but not across sexes. Notably, eight SNPs within a 15-bp region on chromosome 14q31.3 showed excess heterozygosity in both sexes of the African super-population (AFR). Finally, we developed a multivariate predictor of HWD based on sequence features, providing a practical tool that can be integrated into existing quality control pipelines for whole genome sequencing studies.

Journal Article↗