Two novel exonic point mutations in HEXA identified in a juvenile Tay-Sachs patient: role of alternative splicing and nonsense-mediated mRNA decay

LISTERIN E3 Ubiquitin Ligase and Ribosome-Associated Quality Control (RQC) Mechanism

According to cellular demands, ribosomes synthesize and maintain the desired pool of proteins inside the cell. However, sometimes due to defects in ribosomal machinery and faulty mRNAs, these nascent polypeptides are constantly under threat to become non-functional. In such conditions, cells acquire the help of ribosome-associated quality control mechanisms (RQC) to eliminate such aberrant nascent proteins. The primary regulator of RQC is RING domain containing LISTERIN E3 ubiquitin ligase, which is associated with ribosomes and alleviates non-stop proteins-associated stress in cells. Mouse RING finger protein E3 ubiquitin ligase LISTERIN is crucial for embryonic development, and a loss in its function causes neurodegeneration. LISTERIN is overexpressed in the mouse brain and spinal cord regions, and its perturbed functions generate neurological and motor deficits, but the mechanism of the same is unclear. Overall, LISTERIN is crucial for brain health and brain development. The present article systematically describes the detailed nature, molecular functions, and cellular physiological characterization of LISTERIN E3 ubiquitin ligase. Improve comprehension of LISTERIN's neurological roles may uncover pathways linked with neurodegeneration, which in turn might elucidate a promising novel therapeutic intervention against human neurodegenerative diseases.

Atypical juvenile presentation of GM2 gangliosidosis AB in a patient compound-heterozygote for c.259G > T and c.164C > T mutations in the GM2A gene

G_M2-gangliosidosis, AB variant is an extremely rare autosomal recessive inherited disorder caused by mutations in the GM2A gene that encodes G_M2 ganglioside activator protein (GM2AP). GM2AP is necessary for solubilisation of G_M2 ganglioside in endolysosomes and its presentation to β-hexosaminidase A. Conversely GM2AP deficiency impairs lysosomal catabolism of G_M2 ganglioside, leading to its storage in cells and tissues. We describe a 9-year-old child with an unusual juvenile clinical onset of G_M2-gangliosidosis AB. At the age of 3 years he presented with global developmental delay, progressive epilepsy, intellectual disability, axial hypertonia, spasticity, seizures and ataxia, but without the macular cherry-red spots typical for G_M2 gangliosidosis. Brain MRI detected a rapid onset of diffuse atrophy, whereas whole exome sequencing showed that the patient is a compound heterozygote for two mutations in GM2A: a novel nonsense mutation, c.259G > T (p.E87X) and a missense mutation c.164C > T (p.P55L) that was recently identified in homozygosity in patients of a Saudi family with a progressive chorea-dementia syndrome. Western blot analysis showed an absence of GM2AP in cultured fibroblasts from the patient, suggesting that both mutations interfere with the synthesis and/or folding of the protein. Finally, impaired catabolism of G_M2 ganglioside in the patient's fibroblasts was demonstrated by metabolic labeling with fluorescently labeled G_M1 ganglioside and by immunohistochemistry with anti-G_M2 and anti-G_M3 antibodies. Our observation expands the molecular and clinical spectrum of molecular defects linked to G_M2-gangliosidosis and suggests novel diagnostic approach by whole exome sequencing and perhaps ganglioside analysis in cultured patient's cells.

Tay-Sachs Carrier Screening by Enzyme and Molecular Analyses in the New York City Minority Population

Background and Aims: Carrier screening for Tay-Sachs disease is performed by sequence analysis of the HEXA gene and/or hexosaminidase A enzymatic activity testing. Enzymatic analysis (EA) has been suggested as the optimal carrier screening method, especially in non-Ashkenazi Jewish (non-AJ) individuals, but its utilization and efficacy have not been fully evaluated in the general population. This study assesses the reliability of EA in comparison with HEXA sequence analysis in non-AJ populations. Methods: Five hundred eight Hispanic and African American patients (516 samples) had EA of their leukocytes performed and 12 of these patients who tested positive by EA (“carriers”) had subsequent HEXA gene sequencing performed. Results: Of the 508 patients, 25 (4.9%) were EA positive and 40 (7.9%) were inconclusive. Of the 12 patients who were sequenced, 11 did not carry a pathogenic variant and one carried a likely deleterious mutation (NM_000520.4(HEXA):c.1510C>T). Conclusions: High inconclusive rates and poor correlation between positive/inconclusive enzyme results and identification of pathogenic mutations suggest that ethnic-specific recalibration of reference ranges for EA may be necessary. Alternatively, HEXA gene sequencing could be performed.

The first family with Tay-Sachs disease in Cyprus: Genetic analysis reveals a nonsense (c.78G>A) and a silent (c.1305C>T) mutation and allows preimplantation genetic diagnosis

Tay-Sachs disease (TSD) is a recessively inherited neurodegenerative disorder caused by mutations in the HEXA gene resulting in β-hexosaminidase A (HEX A) deficiency and neuronal accumulation of GM2 ganglioside. We describe the first patient with Tay-Sachs disease in the Cypriot population, a juvenile case which presented with developmental regression at the age of five. The diagnosis was confirmed by measurement of HEXA activity in plasma, peripheral leucocytes and fibroblasts. Sequencing the HEXA gene resulted in the identification of two previously described mutations: the nonsense mutation c.78G>A (p.Trp26X) and the silent mutation c.1305C>T (p.=). The silent mutation was reported once before in a juvenile TSD patient of West Indian origin with an unusually mild phenotype. The presence of this mutation in another juvenile TSD patient provides further evidence that it is a disease-causing mutation. Successful preimplantation genetic diagnosis (PGD) and prenatal follow-up were provided to the couple.

•

First patient with Tay-Sachs disease (TSD) in the Cypriot population

•

Silent mutation is a disease causing mutation.

•

Successful preimplantation genetic diagnosis

A novel PAX4 mutation in a Japanese patient with maturity-onset diabetes of the young

Maturity-onset diabetes of the young (MODY) is a genetically and clinically heterogeneous type of diabetes mellitus, characterized by early onset (often before 25 years of age) and absence of pancreatic autoimmunity markers. Paired-homeodomain transcription factor 4 (PAX4) functions as a transcriptional repressor and is involved in the differentiation of insulin-secreting β-cells. Here we identified a novel PAX4 mutation in a Japanese patient with MODY. A 15-year-old, non-obese boy was admitted to our hospital because of polyuria and polydipsia. Laboratory evaluation showed an elevated fasting glucose level; however, islet cell antibodies and glutamic acid decarboxylase antibodies were not detected in the patient's serum. The proband's father had been diagnosed as having type 2 diabetes at age of 30 years. We therefore analyzed several candidate genes of MODY, and identified a novel mutation of a 39-base heterozygous deletion in exon 3 (c.374-412 del39) of PAX4 in the proband and his father. This mutation may cause exon 3 skipping that results in a frameshift, thereby producing a premature stop codon in exon 5. As this mutant PAX4 lacks a part of the homeodomain that is critical for binding to the target gene, this mutant was thought to lose the transcriptional repressor function. As expected, luciferase-reporter assays revealed that the mutant PAX4 could not repress the activities of insulin and glucagon gene promoters, unlike the wild-type PAX4 that repressed the promoter activities. The present study demonstrates that a novel mutation of PAX4 is likely to be associated with diabetes in this Japanese family.