Journal of Medical Genetics最新文献

Background: A substantial fraction of hereditary hearing loss (HL) remains unexplained by known HL genes. Tbx2 is a developmental transcription factor critical for inner ear hair cell differentiation in mice, while its pathogenic role in genetic HL in humans has yet to be documented. Here, we identified heterozygous TBX2 frameshift variants that cause human HL, establishing a previously unrecognised genetic link.

Methods: Linkage analysis combined with whole-genome sequencing (WGS) was applied to identify the causative gene in two unrelated Chinese families with autosomal dominant progressive sensorineural HL (SNHL) accompanied by incomplete penetrance nystagmus. Functional evaluation of TBX2 variants was performed through protein expression, localisation and transcriptional activity analysis in vitro, phenotypic analysis and mechanism study in knockout and knock-in mice model in vivo.

Results: Linkage analysis in Family 1 mapped SNHL to chr17q23.2 (maximum logarithm of odds=3.01), WGS identified two rare heterozygous TBX2 variants (c.977delA, p.Asp326Alafs*42 and c.987delC, p.Ala330Argfs*38) each segregating with the phenotype in a separate family. Affected individuals exhibited isolated auditory and oculomotor phenotypes, without additional syndromic features seen in previously described TBX2-associated disorders. In vitro assays demonstrated that the truncated TBX2 proteins maintained normal expression and nuclear localisation but exhibited 80% reduction in transcriptional activity. In vivo, heterozygous Tbx2 knockout mice (Tbx2^+/- ) developed progressive HL and transient postnatal misexpression of outer hair cell marker in inner hair cells, supporting haploinsufficiency as the pathogenic mechanism.

Conclusion: These findings establish TBX2 as a novel gene for syndromic HL, defining a new autosomal dominant disorder characterised by progressive HL with variable nystagmus. This discovery expands the spectrum of T-box transcription factor disorders and informs molecular diagnosis and genetic counselling in hereditary HL.

Growth retardation, alopecia, pseudoanodontia and optic atrophy (GAPO) syndrome is a rare autosomal recessive disorder caused by biallelic pathogenic variants in the ANTXR1 gene. While significant progress has been made in understanding its molecular basis, no systematic description of the clinical phenotype is available.We conducted a comprehensive review of 105 cases reported in the available literature since the first description of GAPO syndrome in 1947. We summarise here the current understanding of the clinical phenotype and the genetic basis of the condition.Our findings point out the multisystemic nature of GAPO syndrome, primarily featuring skeletal, dermatological and ophthalmological manifestations. The condition is caused by the biallelic loss-of-function of ANTXR1 Histological findings throughout the reported cases underscore the critical role of excessive extracellular matrix deposition in the pathogenesis of GAPO syndrome. The evidence gathered suggests ANTXR1 as an important regulator of extracellular matrix homeostasis.This study highlights the clinical and molecular spectrum of GAPO syndrome. Early recognition, multidisciplinary care and genetic counselling are essential for improving patient outcomes. Future studies should focus on targeted therapies addressing extracellular matrix dysregulation.

SIDT2 (Systemic Interference Deficient 1 Transmembrane Family Member 2) is a lysosomal membrane protein involved in RNA degradation via RNAutophagy. While animal models have indicated a link between SIDT2 deficiency and lysosomal storage disorders, no human cases have been reported. Here, we report a child with biallelic SIDT2 missense variants (p.Arg529Trp, p.Arg678Trp), who developed progressive neurological decline with cerebellar atrophy and Parkinsonian features. Functional studies revealed that the affected individual's variants disrupted the ability of SIDT2 to interact with RNA. Fibroblasts from the affected individual showed impaired autophagy, characterised by abnormal accumulation of autophagy markers. In mouse models, Sidt2 was found to be highly expressed in the brain, particularly in the hippocampus and cerebellum. Sidt2 loss-of-function in mice resulted in not only impaired autophagy in the brain but also neurological dysfunction, including motor incoordination and eventual seizures. These findings suggest that SIDT2 deficiency contributes to both autophagic dysfunction and neurodegenerative processes, providing insight into a potential role in human neurological disease.

Background: Shprintzen-Goldberg syndrome (SGS) shares skeletal features with Marfan syndrome (MFS), but differs in its craniofacial and neurodevelopmental features. Cardiovascular features have been specifically investigated in few of the 57 known patients with SGS described in the literature, making it difficult to determine their prevalence and characteristics.

Methods: We reviewed the medical records of an international cohort of 29 patients, with a particular focus on cardiovascular features. Data were compared with those of MFS.

Results: The sex ratio was 1.9 and median age was 23 years (range: 4-54). 13 patients (44.8%) had mitral regurgitation (MR), 11 (37.9%) had a thoracic aortic aneurysm (TAA) and 9 (31.1%) had aortic regurgitation (AR). No cases of aortic dissection were reported. None had beta-blockers as a primary prevention of aortic events. The Kaplan-Meier method revealed a 30 years risk of 47%, 33% and 22% for occurrence of MR, TAA and AR, respectively. A statistically significant association was found between variants in the Dachshund Homology Domain and the risk of aortic aneurysm (11/20 vs 0/9, p=0.036).

Conclusion: Patients with SGS also significantly have cardiovascular manifestations, encouraging the implementation of a follow-up and preventive cardiovascular treatment identical to that of MFS.

Purpose: To characterise a novel founder variant in the SAG gene causing autosomal dominant retinitis pigmentosa (AD-RP) in Singaporean Chinese individuals.

Design: Single-centre prospective observational cohort study.

Methods: Unrelated probands with AD-RP and their affected relatives were recruited from a tertiary eye hospital in Singapore. Genetic analysis was performed using whole exome sequencing and targeted gene panel testing. Clinical phenotyping included best-corrected visual acuity (BCVA), multimodal imaging and visual field assessments. In silico analyses were conducted to assess variant pathogenicity and conservation.

Results: We identified a novel heterozygous SAG variant, NM_000541.5:c.442G>A (p.Gly148Arg), in five unrelated families of Southern Chinese descent. A shared haplotype of 3.2 Mb among four families suggested a founder effect. Affected individuals presented with mid-life onset nyctalopia (median age 44 years), progressive BCVA loss after age 40 and severe visual field constriction by the fifth decade. Fundus imaging revealed diffuse retinal pigment epithelium atrophy and perivascular pigmentation. In silico predictions suggest that p.Gly148Arg disrupts conformational changes that are required for rhodopsin modulation.

Conclusion: The SAG c.442G>A (p.Gly148Arg) variant represents the first reported SAG-related AD-RP founder variant in ethnic Chinese individuals. Its phenotypic resemblance to the previously described SAG c.440G>T (p.Cys147Phe) variant underscores a common disease mechanism. These findings expand the genetic landscape of AD-RP and highlight SAG as a potential therapeutic target.

Background: Neurofibromatosis type 1 (NF1) is a neurocutaneous condition with tumour predisposition, and patients often face neuropsychiatric and psychosocial challenges. This study aimed to identify unmet needs of NF1 patients in Singapore to enhance patient care and service delivery.

Methods: 20 patients who were clinically or genetically diagnosed with NF1 were recruited for in-depth interviews. Interviews were transcribed verbatim and analysed using thematic analysis.

Results: Five themes emerged from thematic analysis: (1) NF1 trajectory begins from childhood; (2) Coming to terms with body and self; (3) Perceived acceptance drives disclosure patterns; (4) Need for specialised NF1 care; (5) Building local awareness and connections. Six key unmet needs were identified, namely the need for: (1) Optimised multidisciplinary NF1 care; (2) Management of neurological symptoms; (3) Management of cutaneous lesions; (4) Financial coverage for NF1; (5) Early NF1 screening; (6) Local awareness and support groups.

Conclusion: Addressing these needs can lead to actionable steps for improving care and quality of life for NF1 patients in Singapore.

Background: Advances in prostate cancer (PCa) research have revealed dozens of genetic markers for inherited risk. Germline genetic testing (GGT) enhances patient care by guiding therapeutic decisions and promoting screening and surveillance for men and their families. We evaluated the impact of embedding a genitourinary (GU) specialised genetic counsellor (GC) into a multidisciplinary GU clinic on counselling referrals, genetic risk assessment and GGT uptake for men with PCa.

Methods: A chart review of 2593 individuals with PCa from 2016 to 2022 was performed. Categorical data were analysed by the χ² test and predictors were identified by logistic regression.

Results: Prior to the integration of a GU GC (2016-2018), 39 men were referred for genetic counselling (2%), which increased to 368 men (14%) during 2019-2022. During the pre-embedment period, GGT was completed in 9 out of 39 (23%) referrals, whereas GGT was completed in 235 out of 368 referrals (64%) in the postembedment period. Individuals with a younger age (p<0.0001), family history of PCa (p<0.0001), higher Gleason Score (p<0.0001), more advanced clinical stage (p<0.0001), metastatic disease (p<0.0001), and meeting National Comprehensive Cancer Network guidelines for prostate GGT (p<0.0001) were more likely to be referred. Forty-one tested positive for one or more pathogenic or likely pathogenic variants (17%).

Conclusions: The integration of a GC dramatically increased referrals, and a greater proportion of individuals proceeded with GGT. Future studies will analyse barriers and factors promoting referrals so that individuals and their families benefit from evidence-based treatment and early detection and prevention options.

Previous studies have suggested the missense variant NM_000051.4(ATM):c.7271T>G is associated with a high risk of breast cancer (BC), but the magnitude of the association, and the associations with other cancer types, are unclear. Cancer associations were evaluated using sequence data linked to cancer registration data (348 488 participants, 56 640 cancer cases) from UK Biobank (UKB), and targeted sequence or genome-wide array data (126 428 cases, 115 495 controls) from the Breast Cancer Association Consortium (BCAC). The magnitudes of the association of c.7271T>G with invasive BC were similar using UKB (relative risk (RR): 4.57, 95% CI: 2.25 to 9.30, p=2.7×10^-5) and BCAC (OR: 4.11, 2.05 to 8.26, p=6.9×10^-5). In UKB, c.7271T>G was associated with increased risks of prostate cancer (4.84, 2.27 to 10.33, p=4.54×10^-5), and any other cancer (males 2.79, 1.33 to 5.85, p=0.0066; females 3.15, 1.49 to 6.63, p=0.0026). Estimated cumulative risks of all cancers to age 80 years were 87% in males (prostate cancer 43%) and 84% in females (BC 43%). The estimated RRs are consistent with c.7271T>G being associated with a risk of more than twice that for Ataxia-Telangiectasia Mutated protein-truncating variants, for all cancers. These data justify specific management of c.7271T>G carriers.

Background: The γ-actin protein, encoded by the ACTG1 gene, is a critical cytoskeletal component in non-muscle cells. Mutations in ACTG1 are associated with autosomal dominant, progressive sensorineural hearing loss (HL), but clinical heterogeneity remains poorly understood.

Methods: We identified a novel missense variant, c.981C>G (p.Ile327Met; I327M), in a Chinese family with hereditary HL through whole exome sequencing. Functional analyses were performed to assess ACTG1 mRNA and protein expression, F-actin organisation and subcellular localisation. Structural modelling and electrostatic analysis were used to predict the impact of the I327M substitution. Additionally, we reviewed 35 published ACTG1-related families involving 82 patients to explore genotype-phenotype correlations.

Results: The I327M variant resulted in significantly reduced ACTG1 transcript and protein levels, accompanied by disrupted F-actin integrity in patient-derived peripheral blood mononuclear cells. Structural modelling suggested that the variant alters the electrostatic environment near the tropomyosin-binding interface, potentially compromising filament stability. Literature review and comparative analysis revealed that variants located within actin-binding protein (ABP) interaction sites were associated with an earlier onset and more severe progression of HL compared with those located outside ABP-binding domains.

Conclusion: The c.981C>G (p.Ile327Met) variant contributes to HL pathogenesis through dual mechanisms involving impaired gene expression and filament destabilisation. This study highlights the clinical relevance of variant location relative to ABP binding regions and provides new insights into genotype-phenotype relationships in ACTG1-associated HL.

Constitutional or germline pathogenic variants (GPVs) in protection of telomeres 1 (POT1) are associated with a variety of tumours resulting in the recognition of POT1-tumour predisposition syndrome (POT1-TPDS). These tumours may include cutaneous melanoma, angiosarcoma, haematological malignancy and brain tumours. Due to the rarity of POT1 GPVs and limited available data, the overall lifetime cancer risks for individuals with POT1-TPDS are unclear. Furthermore, there is scant evidence to support the role of surveillance in early cancer detection in this patient group. A recent international publication suggested a surveillance protocol similar to that used in Li-Fraumeni Syndrome (LFS) could be offered to POT1 pathogenic variant carriers, particularly where there are LFS-like features. However, current evidence for POT1-TPDS is not supportive of an equivalent lifetime cancer risk. Given the inclusion of POT1 in the National Test Directory in England and the need for UK-based guidance, an expert group undertook a literature review to assess the phenotypic spectrum of POT1-TPDS and to provide lifetime risk estimates of POT1-associated cancers. The available evidence was shared with a small working group of experts that included clinical geneticists, dermatologists, sarcoma specialists, haematologists and radiologists to cover all aspects of the cancers most commonly associated with POT1-TPDS. Following structured expert group discussions, we achieved consensus on best practice recommendations for a POT1-TPDS UK management protocol.