Journal of Medical Genetics最新文献

Introduction: Hypomyelinating leukodystrophies are a group of genetic disorders, characterised by severe permanent myelin deficiency. Their clinical features include developmental delay with or without neuroregression, nystagmus, central hypotonia, progressing to spasticity and ataxia. HSPD1 encodes the HSP60 chaperonin protein, mediating ATP-dependent folding of imported proteins in the mitochondrial matrix. Pathogenic variants in HSPD1 have been related to a number of neurological phenotypes, including the dominantly inherited pure hereditary spastic paraplegia (MIM 605280) and the recessively inherited hypomyelinating leukodystrophy 4 (MIM 612233). Subsequently, an additional phenotype of hypomyelinating leukodystrophy has been reported due to de novo heterozygous HSPD1 variants.In the current work, we expand the clinical and genetic spectrum of this hypomyelinating disorder by describing a cohort of three patients, being heterozygous for HSPD1 variants involving residue Ala536 of HSP60 (the novel p.Ala536Pro variant and the previously reported p.Ala536Val).

Methods: Clinical and radiological evaluation; whole exome sequencing, in vitro reconstitution assay and patient fibroblast cell lysate analysis.

Results: Clinical manifestation was of early-onset nystagmus, tremor and hypotonia evolving into spasticity and ataxia and childhood-onset neuroregression in one case. Brain MRI studies revealed diffuse hypomyelination.The 3D protein structure showed these variants to lie in spatial proximity to the previously reported Leu47Val variant, associated with a similar clinical phenotype. In vitro reconstitution assay and patient fibroblast cell lysate analysis demonstrated that these mutants display aberrant chaperonin protein complex assembly.

Discussion: We provide evidence that impaired oligomerisation of the chaperonin complex might underlie this HSPD1-related phenotype, possibly through exerting a dominant negative effect.

Background: To delineate the clinical and mutational signatures of patients with CRB1-associated retinopathies.

Methods: This multicentre retrospective cohort study involved 40 patients with CRB1 mutations and 40 age-matched and gender-matched inherited retinal diseases (IRDs). The detailed phenotyping and genotyping characteristics and genotype‒phenotype correlations of the patients were analysed.

Results: The mean age of CRB1 cohort was 27.33±14.63 years. Results showed that yellowish geographic macular degeneration (66.67%), small white or yellow dots (65.6%), hyperopia (62.5%), abnormally laminated retina (61.61%), epiretinal membrane (60.6%) and nummular pigment deposits (50%) were the most common signatures in patients with CRB1 mutations. These clinical signatures were notably more prevalent among CRB1 patients than among individuals in other IRD group (p<0.001). Early-onset severe retinal dystrophy/Leber congenital amaurosis (EOSRD/LCA) patients are more likely to present these signatures than retinitis pigmentosa (RP) and macular dystrophy (MD) patients. Furthermore, a significant reduction in central foveal thickness coupled with pronounced thickening of the peripheral retina was observed more distinctly in patients with EOSRD/LCA (p<0.001). The choroidal thickness was not significantly altered compared to the normal controls, but was markedly reduced in the other IRD groups (p<0.001). 55 pathogenic variants were identified, 20 of which were novel. Null mutations were associated with EOSRD/LCA patients, and missense mutations were more prevalent in MD and RP patients.

Conclusions: Key clinical and mutational signatures were demonstrated in this study, providing a comprehensive update on CRB1-associated retinopathies that will aid in diagnosis and lay the foundation for future therapeutic studies.

Pathogenic variants of WD repeat domain 45 (WDR45) cause neurodegeneration with brain iron accumulation 5 (NBIA5), which is characterised by progressive neurological regression and brain iron accumulation in adulthood. Early diagnosis of NBIA5 patients is difficult because they often show only a non-specific developmental delay in childhood, but it is essential for lifelong medical management. We investigated 32 females with developmental delays for coding variants of WDR45 using Sanger sequencing. Whole-genome sequencing (WGS) and X chromosome inactivation (XCI) analysis were also performed. We identified two disease-causing variants, one of which was a novel stop-loss variant, c.1051delG p.(Val351CysfsTer60), in a female with severe developmental delay from early infancy with epileptic spasms. The XCI analysis (which we originally developed) suggested a random pattern in white blood cells. WGS did not reveal any other pathogenic variants, including those in two iron transporter genes. Together with our previous findings in the WGS study, WDR45 variants accounted for 12% (6/51) of the females with developmental delay, suggesting that WDR45 is a major gene in females with developmental delay. Pathogenic variants of WDR45 result in various phenotypes that do not necessarily correlate with variant types or XCI skewing patterns.

Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal disorder, primarily characterised in adults by cutaneous features, pulmonary cysts that predispose to spontaneous pneumothorax and renal tumours. The syndrome is caused by pathogenic variants in the FLCN tumour suppressor gene, which plays a role in the mammalian target of rapamycin (mTOR) signalling pathway. We present the case of a newborn infant diagnosed with BHDS, who died of sudden cardiac death due to complications from cardiac rhabdomyoma. This is only the second reported case of such an association. Both cases were initially misdiagnosed with tuberous sclerosis complex, highlighting the diagnostic challenges. We discuss this differential diagnosis and suggest that cardiac rhabdomyomas, although rare, may be associated with BHDS and potentially life threatening. Therefore, we recommend cardiac screening in newborns at risk.

Background: Facioscapulohumeral muscular dystrophy 1 (FSHD1) is an autosomal dominant muscular disorder mainly caused by the contraction and hypomethylation of the D4Z4 repeat array in chromosome 4q35. Prenatal diagnosis of FSHD1 is challenging due to the highly repetitive and long genomic structure. In this study, a pregnant woman diagnosed with FSHD1 using optical genome mapping sought assistance for a healthy offspring.

Methods: At the 17th week of gestation, she underwent amniocentesis, and genomic DNA (gDNA) was extracted from amniocytes. Whole-genome sequencing of the gDNA was performed using the nanopore MinION platform.

Results: Despite a sequencing depth of only 7.3×, bioinformatic analyses revealed that the fetus inherited four D4Z4 repeat units with the permissive 4qA from the mother and the eight D4Z4 repeat units with the non-permissive 4qB from the father. To validate the results, SNP-based linkage analyses were conducted with gDNA from the proband, the proband's father and proband's amniocytes. Results indicated that the fetus inherited the maternal pathogenic haplotype based on 144 informative SNPs. Linkage analysis was consistent with the nanopore sequencing.

Conclusion: Nanopore sequencing proves to be an accurate and direct method for genetic testing of monogenic diseases at the single-nucleotide level. This study represents the first application of nanopore sequencing in the prenatal diagnosis of FSHD1, providing a significant advantage for patients with de novo mutations.

Objectives: Mutations in the X-linked endosomal Na+/H+ exchanger 6 (NHE6) cause Christianson syndrome (CS). Here, in the largest study to date, we examine genetic diversity and clinical progression in CS into adulthood.

Method: Data were collected as part of the International Christianson Syndrome and NHE6 (SLC9A6) Gene Network Study. 44 individuals with 31 unique NHE6 mutations, age 2-32 years, were followed prospectively, herein reporting baseline, 1 year follow-up and retrospective natural history.

Results: We present data on the CS phenotype with regard to physical growth and adaptive and motor regression across the lifespan including information on mortality. Longitudinal data on body weight and height were examined using a linear mixed model. The rate of growth across development was slow and resulted in prominently decreased age-normed height and weight by adulthood. Adaptive functioning was longitudinally examined; a majority of adult participants (18+ years) lost gross and fine motor skills over a 1 year follow-up. Previously defined core diagnostic criteria for CS (present in>85%)-namely non-verbal status, intellectual disability, epilepsy, postnatal microcephaly, ataxia, hyperkinesia-were universally present in age 6-16; however, an additional core feature of high pain tolerance was added (present in 91%). While neurologic examinations were consistent with cerebellar dysfunction, importantly, a majority of individuals (>50% older than 10) also had corticospinal tract abnormalities. Three participants died during the period of the study.

Conclusions: In this large and longitudinal study of CS, we begin to define the trajectory of symptoms and the adult phenotype thereby identifying critical targets for treatment.

von Hippel-Lindau (VHL) is an autosomal-dominant hereditary tumour susceptibility disease associated with pathogenic germline variants in the VHL tumour suppressor gene. VHL patients are at increased risk of developing multiple benign and malignant tumours. Current CLIA-based genetic tests demonstrate a very high detection rate of germline VHL variants in patients with clinical manifestations of VHL. In this report, we describe a large family with canonical VHL manifestations, for which no germline alteration had been detected by conventional germline testing. We identified a novel 291 kb chromosomal inversion involving chromosome 3p in affected family members. This inversion disrupts the VHL gene between exon 2 and exon 3 and is thereby responsible for the disease observed in this family.

Background: GlcNAc2-epimerase (GNE) myopathy is a rare autosomal recessive disorder caused by pathogenic variants in the GNE gene, which is essential for the sialic acid biosynthesis pathway.

Objective: This multi-centre study aimed to delineate the clinical phenotype and GNE variant spectrum in Chinese patients, enhancing our understanding of the genetic diversity and clinical manifestation across different populations.

Methods: We retrospectively analysed GNE variants from 113 patients, integrating these data with external GNE variants from online databases for a global perspective, examining their consequences, distribution, ethnicity and severity.

Results: This study revealed 97 distinct GNE variants, including 35 (36.08%) novel variants. Two more patients with deep intronic variant c.862+870C>T were identified, while whole genome sequencing (WGS) uncovered another two novel intronic variants: c.52-8924G>T and c.1505-12G>A. Nanopore long reads sequencing (LRS) and further PCR analysis verified a 639 bp insertion at chr9:36249241. Missense variants predominantly located in the epimerase/kinase domain coding region, indicating the impairment of catalytic function as a key pathogenic consequence. Comparative studies with Japanese, Korean and Jewish, our cohorts showed later onset ages by 2 years. The high allele frequency of the non-catalytic GNE variant, c.620A>T, might underlie the milder phenotype of Chinese patients.

Conclusions: Comprehensive techniques such as WGS and Nanopore LRS warrants the identifying of GNE variants. Patients with the non-catalytic GNE variant, c.620A>T, had a milder disease progression and later wheelchair use.

Background: Most schwannomas are isolated tumours occurring in otherwise healthy people. However, bilateral vestibular schwannomas (BVS) or multiple non-vestibular schwannomas indicate an underlying genetic predisposition. This is most commonly NF2-related schwannomatosis (SWN), but when BVS are absent, this can also indicate SMARCB1-related or LZTR1-related SWN.

Methods: We assessed the variant detection rates for the three major SWN genes (NF2, LZTR1 and SMARCB1) in 154 people, from 150 families, who had at least one non-vestibular schwannoma, but who did not meet clinical criteria for NF2-related SWN at the time of genetic testing.

Results: We found that 17 (11%) people from 13 families had a germline SMARCB1 variant and 19 (12%) unrelated individuals had a germline LZTR1 variant. 19 people had an NF2 variant, but 18 of these were mosaic and 17 were only detected when 2 tumours were available for testing. The overall detection rate was 25% using blood alone, but increased to 36% when tumour analysis was included. Another 12 people had a germline variant of uncertain significance (VUS).

Conclusions: There were similar proportions of LZTR1, SMARCB1 or mosaic NF2. However, since an NF2 variant was detected in tumours from 103 people, it is likely that further cases of mosaicism would be detected if more people had additional tumours available for analysis. In addition, if further evidence becomes available to show that the VUSs are pathogenic, this would significantly increase the proportion of people with a genetic diagnosis. Our results indicate the importance of comprehensive genetic testing and improved variant classification.