Journal of Medical Genetics最新文献

Background: Short-read genome sequencing (sr-GS) affords efficient and accurate characterisation of apparently balanced chromosomal rearrangement (ABCR) breakpoints except in 9%-11% of cases that remain undetectable.

Methods: Among 117 ABCR that we studied in patients with abnormal phenotype, 14 (11.9%) could not be detected by our current strategy including sr-GS, alignment against the GRCh38 reference genome and structural variant (SV) detection using Breakdancer V.1.4.5. These were all reciprocal translocations, 10 of which implicated constitutive heterochromatin, acrocentric short arms or pericentromeric regions. We re-aligned the sequencing data against the T2T-CHM13 V.2.0 reference genome and re-analysed them using five other SV callers (DELLY, GRIDSS, LUMPY, Manta and SvABA). In addition, 11 ABCRs were further characterised using FISH, linked-read sequencing, long-read sequencing or optical genome mapping, either isolated or combined.

Results: We were able to characterise the breakpoints at the bp level for 12 translocations and identify specific breakpoint patterns using Integrative Genome Viewer (IGV). In each translocation, at least one breakpoint involved highly repetitive elements such as alpha-satellites, segmental duplications, satellite repeats or other poorly mapped regions. For six out of 12 patients, one of the breakpoints could explain the phenotype either by gene disruption (CAMTA1, DYRK1A, NLGN4X) or position effect (BMP2, DIAPH2, SIX3).

Conclusion: Failure of sr-GS is due to highly repetitive genomic regions at SV breakpoints, either absent from the reference genome or not attributed to a unique position. The resolution of ABCRs is essential to patients' care since it allowed us to conclude to a pathogenic variant in 50% of patients.

RNU4ATAC is a non-coding gene involved in the minor spliceosome, and is mutated in a spectrum of syndromic skeletal disorders with recessive inheritance. Recently, biallelic RNU4ATAC pathogenic variants were detected in five patients presenting a complex syndromic phenotype and a brain malformation resembling the 'molar tooth sign' (MTS). This is the hallmark of Joubert syndrome (JS), a neurodevelopmental ciliopathy with multiorgan involvement.We reanalysed exome sequencing (ES) from 53 patients with JS, who lacked coding variants in known JS-associated genes. Four RNU4ATAC variants (n.16G>A, n.51G>A, n.13C>T and n.30G>A) were identified in compound heterozygosity in three probands, accounting for 5.6% of negative cases. All patients displayed the MTS and clinical features overlapping those of JS and RNU4ATAC-related skeletal disorders.These findings expand the phenotypic spectrum of RNU4ATAC-related disorders to include a complex neurological-skeletal ciliopathy phenotype, and highlight the relevance of ES reanalysis to uncover non-coding variants often undetected by conventional diagnostics.

Background: While AUTS2 is recognised as a pivotal neurodevelopmental gene, its role in skeletal morphogenesis has remained unexplored. We investigated the contribution of AUTS2 to radioulnar synostosis (RUS) and associated skeletal dysplasias through integrated molecular and phenotypic analyses of unrelated probands.

Methods: Comprehensive genetic profiling was performed on patients with RUS, including G-banding karyotyping, translocation breakpoint mapping via low-coverage whole-genome sequencing with PCR/Sanger validation, CNV detection using SNP array (Infinium OmniZhongHua-8) and qPCR, and exome sequencing followed by orthogonal Sanger confirmation.

Results: Four novel pathogenic AUTS2 variants were identified from four unrelated patients: a balanced translocation [46,XY,t(7;21)(q11.22;q21.1)] disrupting intron 5 (hg19:chr7:71,845,797); a heterozygous 2.99 Mb deletion (hg19:7q11.22[67,488,531-70,480,818]) spanning AUTS2 and flanking loci; and two de novo frameshift insertions (c.47_48insG; c.864_865insGGACTGTTGCAAAGAGCCA). All variants impaired the full-length AUTS2 transcript. Affected individuals exhibited RUS accompanied by additional skeletal anomalies (micrognathia, short stature, dysplasia of hip joint, tight heel cords) and other AUTS2 syndrome features. Notably, phenotypic overlap with Tsukahara syndrome (OMIM 603438) was observed, suggesting potential diagnostic continuity between these entities.

Conclusion: This study establishes AUTS2 as a critical regulator of skeletal development, with molecular disruptions directly linked to RUS pathogenesis and broader skeletal dysmorphogenesis.

Background: Inherited retinal diseases (IRDs) are a group of disorders often resulting in progressive vision loss, ultimately leading to blindness. A significant portion of their genetic causes remain unresolved, partly due to undiscovered disease-associated genes or variants. This study aimed to identify novel genetic links to IRDs.

Methods: All patients underwent comprehensive ophthalmological evaluation, including retinal imaging (fundus autofluorescence and macular optical coherence tomography) and electroretinogram testing. Whole exome sequencing and whole genome sequencing were performed on patients with clinically unsolved IRD, and data were analysed using an in-house pipeline to identify causal variants. Subsequently, Sanger sequencing was performed to confirm identified variants.

Results: Three unrelated patients from Europe, Middle East and East Asia were identified with unique late-onset retinal degeneration (Stargardt-like phenotype) associated with biallelic loss-of-function (LoF) variants in C19orf44 (HGNC: 26141), a gene of unknown function. The homozygous variant NM_032207.2:c.549_550del;p.Ser185Profs*2 was identified in two unrelated patients (European and Middle Eastern). Moreover, an East Asian patient had likely compound heterozygous LoF variants (NM_032207.2:c.1168C>T;p.Gln390*/c.976_977del;p.Leu326Lysfs*15).

Conclusions: Our findings establish C19orf44 as a novel disease-causing gene for IRD with Stargardt-like phenotype, expanding the genetic landscape of retinal degeneration.

Background: Autosomal dominant (AD) inheritance often arises through haploinsufficiency, dominant-negative or gain of function (GoF) effects, while autosomal recessive (AR) inheritance generally results from partial or complete loss of function (LoF). Yet, a subset of genes demonstrates both inheritance patterns. We aimed to curate a list of such 'AD/AR' genes and to propose additional candidates.

Methods: AD/AR genes were subcategorised based on genotype-phenotype correlations and disease mechanisms. Using bioinformatic analyses, we compared genes with AD, AR and AD/AR inheritance across various metrics, including gnomAD constraint values, exon count, protein length, quaternary structure and gene ontology terms. A machine learning-based metric was used to account for interdependence among features.

Results: Pathogenic variants in AD/AR genes can lead to distinct or similar phenotypes, depending on the molecular mechanism. AD/AR genes exhibit unique bioinformatic properties such as intermediate constraint scores, a combination of gene ontology terms, a greater average number of exons and an elevated propensity to form homomeric/heteromeric proteins. We identified homozygous LoF or clinically reported variants in nine genes previously classified as AD only.

Conclusion: Collectively, the data suggest that AD/AR genes possess distinctive features that likely underpin their dual inheritance modes. We propose nine candidate AD/AR genes and emphasise caution in filtering by inheritance type alone.

11β-hydroxylase deficiency (11βOHD) is the second most common cause (5%) of congenital adrenal hyperplasia (CAH). The CYP11B1 gene shares 95% of genomic sequence homology with CYP11B2, and therefore Sanger sequencing remains the gold standard. We present a case of 11βOHD due to an intragenic inversion in CYP11B1 that was missed by both the Sanger sequencing and massive parallel sequencing (MPS) methods. The child was born with virilised genitalia at Prader stage 4 and the biological findings showed a hydromineral retention pattern and a pathognomonic increase in steroid precursors suggestive of 11βOHD. Standard trio analysis revealed only one heterozygous pathogenic variation inherited from the father. The study using MPS showed similar outcomes. Careful observation of the alignment BAM files revealed breaks in sequencing depth, incomplete alignments and systematic paradoxical read-pairs orientation. A specifically designed amplification and Sanger protocol confirmed the novel NM_000497.4(CYP11B1):c.[892_1121+7 inv;1121+8_1121+9del]; p.(Glu298HisfsTer113) variant at heterozygous state in the proband and his mother, fulfilling the diagnosis. The present case reports the first short intragenic inversion in CAH and illustrates the pitfalls that must always be kept in mind when using sequencing methods. When the phenotype is unequivocal, a thorough investigation of the locus should be carried out with cross-use of different techniques.

In the UK, most patients receive publicly funded medical care through the National Health Service (NHS), which funds tumour and/or germline testing for eligible patients with cancer to inform clinical management.Testing on tumour-derived DNA may identify putative heritable variants, with implications for the proband and their wider family, but is not a reliable substitute for germline genetic testing when hereditary cancer predisposition is suspected.The likelihood that a variant identified through tumour testing is of germline origin depends on multiple clinical and technical factors. Certain genotypes significantly influence a patient's cancer risk, and intervention in those carriers may facilitate cancer prevention or early detection, while other genotypes are associated with lower cancer risk, and associated intervention in such cases have limited clinical utility.We convened a national meeting of clinical cancer genetics and scientific leads to rationalise germline follow-up testing of variants identified through tumour-based testing. After contrasting potential approaches, implementation of an NHS-contextualised 'intermediate conservative' approach was agreed and refined by the authors, with the final pathway recirculated to the UK clinical and scientific community for consensus agreement and publication.We outline relevant patient, genetic and technical considerations informing likely origin of variants, a review of current relevant guidance and NHS laboratory practices and a workflow for laboratory and clinical teams to triage tumour-detected variants requiring onward germline follow-up. This approach aims to direct limited resources towards identifying germline variants associated with the greatest potential clinical impact, with a view to supporting more efficient and equitable delivery of genomic medicine in oncology.

Background: Facioscapulohumeral muscular dystrophy 1 (FSHD1) is one of the most common autosomal dominant neuromuscular diseases. Genetic diagnosis of FSHD1 remains a challenge because of the long length and repetitive nature of D4Z4 repeats. Long-read sequencing is an effective method for detecting FSHD1, but sequencing depth remains a limitation.

Methods: We developed a long-read library adaptive sampling (LRL-AS) method based on Oxford Nanopore Technologies (ONT) sequencing to comprehensively detect FSHD1. Two patients were sequenced by adaptive sampling, followed by analyses of D4Z4 repeat units (RUs), methylation and haplotype.

Results: Compared with whole-genome sequencing, our LRL-AS method shows significant improvements in both sequencing depth and read length. LRL-AS can identify D4Z4 RUs contraction with accuracy comparable to optical genome mapping in both 4q35 and 10q26 regions. We also calculated methylation levels in the double homeobox 4 (DUX4) gene region. With the benefit of higher sequencing depth, allele-specific methylation can be calculated with greater precision. We also observed that, at different sequencing depths, ONT sequencing data consistently provide stable calculations of methylation levels. More importantly, we demonstrated that data from adaptive sampling can be effectively used to construct the haplotype of the pathogenic allele using single-nucleotide polymorphisms.

Conclusion: Our LRL-AS method is a comprehensive approach for FSHD1 detection, improving the accuracy of D4Z4 RUs and methylation detection while enabling allele-specific haplotype construction. It holds promising potential for clinical application.

Background: Duplication of the pituitary gland (DPG)-plus syndrome is an extremely rare developmental malformation of unknown aetiology.

Methods: Two unreported patients of DPG-plus syndrome are described. Underlying genetic defects were explored, including chromosomal microarray (CMA), whole exome sequencing (WES) and mRNA analysis. A literature review was presented.

Results: Patient 1 had DPG, palatal cleft, bifid tongue, intraoral teratoma, lingual hamartoma and duplicated basilar artery and odontoid process. Patient 2 had DPG, epignathus teratoma, a nasal mass, choanal atresia, cleft palate, bifid tongue, abnormal basilar artery and fused upper cervical spine. CMA yielded normal results. WES of patient 1 disclosed a novel splice site PTCH2 variant, c.1590+1G>A, leading to exon 12 skipping and an in-frame deletion of 44 amino acids. WES of patient 2 revealed no candidate variants. A literature review of 51 cases showed mostly reported in childhood and female sex (80%). The leading anomalies identified included DPG (100%), cleft palate (68.6%), anomalous cervical spine (56.9%), hypothalamic mass/enlargement (58.8%), intraoral teratoma (58.8%), basilar arterial abnormalities (43.1%) and bifid/trifid tongue (23.5%). Non-craniofacial anomalies were found in <10% of cases. Late complications included precocious puberty, all in female patients, and hypogonadotropic hypogonadism in a few patients.

Conclusions: Two new cases of DPG-plus syndrome were reported, with rare findings of epignathus and choanal atresia. We propose that DPG-plus syndrome may result from a double hit in one of the genes involved in SHH signalling, arising from a germline pathogenic variant with mosaicism for a somatic pathogenic variant or digenic/oligogenic inheritance of the SHH signalling-related genes.