Journal of Human Genetics最新文献

NGLY1 deficiency is a rare autosomal recessive genetic disorder caused by biallelic mutations of the human NGLY1 gene. NGLY1 encodes the cytosolic peptide:N-glycanase (PNGase; NGLY1 in mammals), which plays essential roles in cytosolic glycan degradation (non-lysosomal glycan degradation), the endoplasmic reticulum (ER)-associated degradation (ERAD) of misfolded proteins, and the complete activation of the transcription factor nuclear factor erythroid 2-like 1 (NEF2L1). NFE2L1 contributes to the regulation of the expression of proteasome subunits and oxidative stress responses. Patients with NGLY1 deficiency exhibit multisystemic clinical features, including global developmental delay, peripheral neuropathy, hypolacrima or alacrima, and the transient elevation of liver transaminases. To date, more than 100 individuals with NGLY1 deficiency and over 70 distinct pathogenic mutations in the NGLY1 gene have been reported. There is currently no approved therapy for this disorder. Moreover, the underlying pathogenic mechanism, including the correlation between patients' symptoms and mutant alleles, remains poorly understood. In this review, we summarize the most frequently reported NGLY1 mutations and their associated clinical features. We also present an overview of the current therapeutic strategy for NGLY1 deficiency.

The J-domain proteins (JDPs), or HSP40s, are essential molecular co-chaperones that, in concert with HSP70, play a pivotal role in maintaining protein homeostasis, which is particularly critical in skeletal muscle. In recent years, pathogenic variants in several JDP-encoding genes have been identified as a cause of a growing group of inherited muscle diseases, termed JDP-related myopathies. This review provides a comprehensive overview of the current understanding of the molecular genetics, clinical phenotypes, muscle pathology, and pathomechanisms of myopathies caused by mutations in DNAJB6, DNAJB4, and DNAJB2. These disorders present with a wide spectrum of clinical features, including limb-girdle or distal weakness, and, in some cases, severe early-onset respiratory failure with axial rigidity. Pathologically, they are often characterized by rimmed vacuoles and sarcoplasmic protein inclusions. The underlying molecular mechanisms all involve disruption of the JDP-HSP70 chaperone system, but they are driven by distinct molecular events specific to each gene and mutation type. While loss-of-function is a primary mechanism for recessive forms of DNAJB4 and DNAJB2 myopathy, a toxic gain-of-function mediated by a dysregulated interaction with HSP70 is emerging as a central pathomechanism for dominant myopathies caused by DNAJB6 and DNAJB4 variants. A dominant-negative effect is proposed for dominant DNAJB2 neuromyopathy. This evolving mechanistic understanding is crucial as it informs the development of targeted therapeutic strategies, moving beyond supportive care. Potential future therapies include gene replacement for loss-of-function disorders, and for gain-of-function diseases, approaches including small molecule inhibitors of the JDP-HSP70 interaction or allele- and isoform-specific knockdown.

The clinical relevance of glycans, which play a wide array of physiological roles, is underscored by the emergence of congenital disorders of glycosylation, a group of rare inherited diseases caused by defects in glycan-related genes (glycogenes). Biochemical studies of recombinant proteins and phenotypic analyses in knockout mice are revealing critical insights into the roles of various glycosyltransferases, glycosidases, and glycan-binding proteins. However, the biological functions of numerous glycogenes and their role in disease remain incompletely understood, partly due to human-specific functions that are not recapitulated in model organisms, and partly due to the structural diversity and complexity of glycan modifications, which are difficult to fully assess by conventional methods. A promising complementary strategy is the systematic assessment of human genetic variants, particularly missense mutations, to infer functional consequences. Recent developments in protein structure prediction, exemplified by AlphaFold, are facilitating the development of structure-based approaches to variant interpretation. In this review, we discuss current methodologies for predicting the impact of missense variants using structural information, and introduce VarMeter, a computational framework incorporating 3D structural parameters that has been successfully applied to the prediction of pathogenic variants in the ClinVar database. We also describe VarMeter2, an updated version that integrates AlphaFold-derived pLDDT confidence scores and Mahalanobis distance analysis to improve prediction accuracy, demonstrating its ability to predict pathogenic variants of four glycan-related proteins. These tools offer a novel avenue for uncovering previously unrecognized functions of glycogenes and their links to disease, and contribute to the clinical interpretation of genetic variation.