Molecular Genetics & Genomic Medicine最新文献

Background: POU4F3 mutations cause DFNA15, an autosomal dominant nonsyndromic hearing loss. POU4F3 encodes a transcription factor crucial for inner ear hair cell development and maintenance.

Objective: To identify and functionally characterize novel POU4F3 mutations in two Chinese families with late-onset progressive hearing loss.

Methods: Massively parallel DNA sequencing (MPS) was performed on affected individuals from two unrelated Chinese families. Sanger sequencing validated mutations and confirmed co-segregation. Functional analyses included protein expression analysis by Western blots and subcellular localization studies by immunofluorescence.

Results: We identified two novel nonsense mutations in POU4F3: c.863C > A (p.Ser288Ter) and c.172G > T (p.Glu58Ter), both co-segregating with the hearing loss phenotype. Functional studies showed p.Ser288Ter produced a stable but mislocalized protein with impaired nuclear transport, while p.Glu58Ter resulted in a severely truncated, rapidly degraded protein.

Conclusion: This study expands the DFNA15 mutation spectrum and provides new insights into POU4F3-related hearing loss pathogenesis. Our findings demonstrate that different molecular mechanisms can lead to similar DFNA15 phenotypes, supporting POU4F3 haploinsufficiency as the primary pathogenic mechanism.

Background: Biallelic variants of COL18A1 cause Knobloch syndrome (KNO), a rare genetic disorder, characterized by oculopathy and structural defects. Recently, several studies have suggested that novel de novo missense variants in PAK2 may be associated with KNO; however, there are few case reports. This study aimed to investigate a patient with KNO who initially presented with seizures and expand the PAK2 genotype and phenotype spectrum.

Methods: This study included a Chinese family with a proband who primarily presented with epilepsy and developmental delay. Whole-exome sequencing and Sanger sequencing were performed to analyze potential variants. Structural modeling was performed to assess the impact of the variant on the protein structure. In vitro, a mutant plasmid was constructed and transfected into 293T cells to conduct phosphorylation assays, and phosphorylation levels at Ser141 of PAK2 were assessed. The PAK kinase inhibitor FRAX597 was used to confirm the specificity of the western blot results.

Results: A de novo variant of PAK2 gene, NM_002577.4: c.1049G>A (p.Arg350Lys) was found in the patient but not in his parents or sister. This variant was found to be located in the kinase domain and may alter the hydrogen-bond network, potentially affecting kinase activity. In vitro functional experiments demonstrated that the variant may lead to reduced protein levels. Moreover, Western blot analysis showed a significant decrease in the phosphorylation level at Ser141 compared to the wild-type plasmid, indicating that the variant may lead to decreased PAK2 phosphorylation levels.

Conclusion: The clinical manifestations in this patient may be associated with a novel PAK2 variant, and the atypical presentation of KNO suggests that PAK2-related KNO may have a broader phenotypic spectrum.

Background: LUMBAR syndrome is the association of segmental infantile hemangiomas that affect the Lower part of the body with Urogenital anomalies, hemangioma Ulceration, spinal cord Malformations, Bony deformities, Anorectal malformations, Arterial anomalies and/or Renal anomalies. The etiology is not known but is suspected to be multifactorial, involving genetic and environmental factors.

Methods: We retrospectively reviewed a large database of 109 published reports of LUMBAR syndrome to study potential associated clinical risk factors, the first such effort.

Results: LUMBAR is significantly more common in full-term, normal birth weight, singleton girls. We found no statistically significant differences in disease severity between affected girls and boys. There were no reports in twins or other multiple births, no reports of familial recurrence, and no repeated maternal illnesses, exposures, or other prenatal risk factors.

Conclusions: Prospective studies in LUMBAR syndrome are needed to further evaluate maternal risk factors for prenatal hypoxia, gene-environment interactions, and genetic susceptibility variants.

Background: SLC26A4 is the second most common cause of hereditary hearing loss worldwide. This gene predominantly harbors pathogenic variants, including splice, nonsense, and missense. Although missense variants are relatively common, their specific effects on protein function remain unclear. Consequently, there is an urgent need to establish an in vitro system to investigate how these variants impact SLC26A4 protein function.

Methods: Genetic testing was conducted to determine the specific types of underlying genetic variants in patients. Following this, we employed plasmid transfection to evaluate the effects of the variants on both protein expression levels and the protein's subcellular localization. Thereafter, we transformed peripheral blood mononuclear cells (PBMCs) from the proband into induced pluripotent stem cells (iPSCs) through Sendai virus-mediated transduction.

Results: Genetic testing revealed that the proband carried compound heterozygous variants: SLC26A4 c.919-2A > G and c.317C > A. The c.317C > A variant markedly decreased the expression levels of SLC26A4 mRNA and its encoded protein. Additionally, it led to the protein's accumulation in the cytoplasm as aggregates. We successfully reprogrammed peripheral blood mononuclear cells from the proband into induced pluripotent stem cells (iPSCs) and verified that these iPSCs retained their pluripotency, differentiation potential, and genetic integrity.

Conclusion: These results provide important insights into the mechanisms by which SLC26A4 gene variants lead to hearing loss.

Background: Developmental epileptic encephalopathy 56 (DEE56) is a monogenic DEE type caused by heterozygous mutations in YWHAG. To our knowledge, fewer than 30 cases of DEE56 have been reported globally, and our understanding of YWHAG's function remains limited.

Methods: Whole exome sequencing (WES) was performed on the patient and his parents. Structural conservation analysis of YWHAG was conducted using Consurf and PyMol. A literature search for relevant cases was performed in PubMed and Google Scholar.

Results: The patient is a 6-year-2-month-old boy who developed refractory complex seizures starting at 8 months of age. He also exhibits intellectual disability, language impairment, and poor motor coordination. WES identified the de novo occurrence of a novel heterozygous YWHAG missense variant, c.518T>C (p.L173S), in the patient. L173 resides within the hydrophobic internal core formed by three alpha helices of YWHAG, and the residues constituting this internal core are highly evolutionarily conserved. The L173S substitution introduces a hydrophilic side chain into the hydrophobic core composed of three aliphatic residues. Ten missense mutations have been reported previously. Among them, five (E15, R57, D129, R132, and Y133) are associated with the ligand-binding region.

Conclusion: The functional domain involving the L173 residue of YWHAG remains unknown. Our findings suggest that the disruption of the stability of the highly conserved internal core of the YWHAG protein may be one mechanism leading to functional impairment, distinct from the previously proposed pathogenic models of dimer formation defects and/or impaired binding to phosphopeptide ligands. This may provide insights into the functional mechanisms of YWHAG and potential therapeutic strategies.

Background: Multiple molecular diagnoses (MMD) involve distinct or overlapping phenotypes. They are not so rare in the field of congenital anomalies, given an overall 3.5%-8% rate. Mainly, MMD imply distinct genotypes. Exceptionally, genotypes are linked, involving a causal CNV by itself, facing a SNV for a recessive disorder resulting in a dual diagnosis.

Methods: An unrelated couple was referred at 21 + 3 weeks of gestation for talipes equinovarus, cerebellar hypoplasia, clenched fists, elevated hemidiaphragm, and micrognathia. Chromosomal microarray and exome sequencing analyses were performed.

Results: Both identified a pathogenic de novo 22q11.21 deletion (22q11.2del). Fetal autopsy revealed additional features (postaxial polydactyly, facial features, and abnormal lung lobulation), atypical for 22q11.2del syndrome. At the clinician's request, exome sequencing reanalysis identified a paternally inherited SCARF2 variant, in trans to the 22q11.2del causing autosomal recessive Van den Ende-Gupta syndrome. This dual diagnosis explains the entire fetus phenotype.

Discussion: This is a novel case of dual diagnosis, first prenatal and second case of this ultrarare association. It reflects the crucial role of precise phenotypic description, combined with the importance of considering dual diagnosis in case of atypical clinical presentation. Finally, prenatal phenotypes remain a challenge given the paucity of available known prenatal data for most rare diseases.

Trial registration: ClinicalTrial.gov ID: NCT05182242.

Background: Vascular Ehlers-Danlos syndrome (vEDS) is caused by alterations in the COL3A1 gene, typically involving missense variants that replace glycine residues. In contrast, short in-frame insertions, deletions, and duplications are rare and pose significant challenges for investigation.

Methods: The histological examination of vascular tissue from a 26-year-old man, who died from a common iliac artery aneurysm and whose mother died at age 60 from an abdominal aortic dissection, strongly suggested a diagnosis of Ehler-Danlos type IV. Ex vivo collagen phenotype assessment, molecular analysis, and in silico structural studies of type III collagen were subsequently performed.

Results: Ex vivo analysis of the patient's fibroblasts revealed altered collagen synthesis, whereas the molecular testing identified a novel 18-nucleotide in-frame duplication (c.2868_2885dup-GGGTCTTGCAGGACCACC) in the COL3A1 gene, resulting in a six-amino acid insertion, p.(Leu958_Gly963dup). Structural investigation indicated that this duplication led to a local perturbation of the collagen triple helix near a metalloproteinase cleavage site.

Conclusion: This study highlights the pathogenic role of a novel in-frame duplication in the COL3A1 gene, demonstrating how this seemingly benign alteration significantly compromises collagen turnover and contributes to the development of vEDS.

Background: Mitochondrial short-chain enoyl-CoA hydratase 1 deficiency (ECHS1D) is a rare autosomal recessive disorder affecting valine metabolism, with clinical severity ranging from neonatal death to survival into adulthood. Despite advances in understanding ECHS1D, the genetic basis remains underexplored, particularly in underrepresented populations.

Methods: This study aimed to investigate the clinical and genetic characteristics of ECHS1D in two unrelated Chinese families and identify novel pathogenic variants. Clinical and genetic data were collected, and whole-genome sequencing was performed to identify pathogenic variants in the ECHS1 gene.

Results: The first proband, a 15-month-old girl, presented with developmental delays and metabolic acidosis, with an MRI revealing abnormal signals in the basal ganglia. The second proband, a 6.5-year-old girl with movement-induced dystonia, exhibited lethargy following recurrent fever and vomiting, with similar MRI findings. Genetic testing identified novel compound heterozygous variants: c.759_762del (p.Gly255Valfs*21) and c.489G>A (p.Pro163=) in Proband 1 and c.518C>T (p.Ala173Val) and c.244G>A (p.Val82Met) in Proband 2. The c.759_762del (p.Gly255Valfs21) variant, identified for the first time, likely results in severe symptoms due to a loss of normal function.

Conclusion: These findings expand the ECHS1 mutational spectrum and emphasize the importance of genetic testing for early diagnosis and personalized management of ECHS1D. Interventions such as dietary valine restriction and the avoidance of triggering factors may improve clinical outcomes, while further research is needed to explore targeted therapeutic strategies.

Background: CDG2L (MIM#614576) is an autosomal recessive multisystemic disorder due to variants in COG6 gene. Postnatal phenotypes are now well described, while prenatal presentations remain poorly investigated. Only 8 of the 28 published patients have had prenatal ultrasound anomalies reported and no one post-mortem investigation.

Methods: We used whole-exome sequencing in a consanguineous Turkish family with four siblings presenting with Pierre Robin sequence, arthrogryposis, heart malformation, splenomegaly, hydrocephaly, corpus callosum dysgenesis, brainstem, and cerebellar hypoplasia.

Results: We identified a novel homozygous pathogenic variant in exon 9 of COG6 (NM_020751.2): c.821del, p.(Arg274Lysfs*32). In this family, our post-mortem study led us to describe further the prenatal phenotype of CDG2L. In addition, it permits correlating the most relevant anomalies to a maldevelopmental cascade due to a neurodegenerative process of metabolic origin, affecting the entire central nervous system including the spinal cord.

Conclusion: In this context of recurrence of multisystemic disease diagnosed antenatally, exome sequencing is powerful to give a precise diagnosis and allows proposing a molecular prenatal diagnosis at the following pregnancy.

Background: The obscurin protein encoded by the OBSCN gene is an important structural protein in the regulation of myocyte sarcoplasmic nodule stability and sarcoplasmic reticulum function and is particularly closely associated with calcium ion (Ca²⁺) signaling. With increasing genomic studies, pathogenic variants in the OBSCN gene have been shown to be associated with a variety of inherited diseases, such as cardiomyopathy. However, case reports of its variants causing rhabdomyolysis are more limited.

Methods: We performed whole exome sequencing on a patient with exercise-induced rhabdomyolysis to identify possible causative gene variants. In addition, functional prediction of the pathogenicity of the variants was performed by combining multiple bioinformatics analysis tools and in-depth analyses with clinical phenotypes and family history.

Results: The patient carried compound heterozygous variants, including c.21184C>T (nonsense variant) and c.15610+12C>T (intronic splicing variant). The c.21184C>T variant resulted in a premature termination of the protein, was not included in population-based databases, and was supported by multiple prediction tools as a potentially pathogenic variant. The c.15610+12C>T variant was also absent in the gnomAD_EAS database and predicted to disturb normal splicing, potentially creating a novel donor site. The pathogenicity of the variant is further supported by the fact that the patient's mother, with a homozygous OBSCN variant, also exhibited exercise-induced myalgia. Clinically, the patient presented with exercise-induced rhabdomyolysis accompanied by significant serum creatine kinase elevation, muscle pain, and MRI-demonstrated muscle edema of both lower limbs without significant muscle weakness or cardiac abnormalities.

Conclusion: We report the first case of rhabdomyolysis in China caused by OBSCN gene variants. This finding further extends the spectrum of the OBSCN gene variants. It also provides an important basis for genetic counseling and helps in the early diagnosis and management of similar cases.