Analysis of lysosomal enzyme activity and genetic variants in a child with late-onset Pompe disease / 中华医学遗传学杂志

OBJECTIVE@#To explore the clinical features, lysosomal enzymatic [acid α-glucosidase (GAA)] activities and genetic variants in a child with late-onset Pompe disease (LOPD).@*METHODS@#Clinical data of a child who had presented at the Genetic Counseling Clinic of West China Second University Hospital in August 2020 was retrospectively analyzed. Blood samples were collected from the patient and her parents for the isolation of leukocytes and lymphocytes as well as DNA extraction. The activity of lysosomal enzyme GAA in leukocytes and lymphocytes was analyzed with or without addition of inhibitor of GAA isozyme. Potential variants in genes associated with neuromuscular disorders were analyzed, in addition with conservation of the variant sites and protein structure. The remaining samples from 20 individuals undergoing peripheral blood lymphocyte chromosomal karyotyping were mixed and used as the normal reference for the enzymatic activities.@*RESULTS@#The child, a 9-year-old female, had featured delayed language and motor development from 2 years and 11 months. Physical examination revealed unstable walking, difficulty in going upstairs and obvious scoliosis. Her serum creatine kinase was significantly increased, along with abnormal electromyography, whilst no abnormality was found by cardiac ultrasound. Genetic testing revealed that she has harbored compound heterozygous variants of the GAA gene, namely c.1996dupG (p.A666Gfs*71) (maternal) and c.701C>T (p.T234M) (paternal). Based on the guidelines from the American College of Medical Genetics and Genomics, the c.1996dupG (p.A666Gfs*71) was rated as pathogenic (PVS1+PM2_Supporting+PM3), whilst the c.701C>T (p.T234M) was rated as likely pathogenic (PM1+PM2_Supporting+PM3+PM5+PP3). The GAA in the leukocytes from the patient, her father and mother were respectively 76.1%, 91.3% and 95.6% of the normal value without the inhibitor, and 70.8%, 112.9% and 128.2% of the normal value with the inhibitor, whilst the activity of GAA in their leukocytes had decreased by 6 ~ 9 times after adding the inhibitor. GAA in lymphocytes of the patient, her father and mother were 68.3%, 59.0% and 59.5% of the normal value without the inhibitor, and 41.0%, 89.5% and 57.7% of the normal value with the inhibitor, the activity of GAA in lymphocytes has decreased by 2 ~ 5 times after adding the inhibitor.@*CONCLUSION@#The child was diagnosed with LOPD due to the c.1996dupG and c.701C>T compound heterozygous variants of the GAA gene. The residual activity of GAA among LOPD patients can range widely and the changes may be atypical. The diagnosis of LOPD should not be based solely on the results of enzymatic activity but combined clinical manifestation, genetic testing and measurement of enzymatic activity.

[The] identification of Pompe disease mutations in archival tissues and development of a rapid molecular-based test

Pompe disease [glycogen storage disease type II] is a rare autosomal recessive lysosomal storage disease that is caused by acid alpha-glucosidase deficiency. Early enzyme replacement therapy can benefit infants with the disease but the diagnosis is complicated by the rarity of the disease and the heterogeneity of the clinical manifestations. In this study, DNA extracted from archival postmortem formalin-fixed paraffin-embedded tissues was used to identify Pompe disease mutations in Oman and develop a rapid molecular-based test. Intronic primers were designed to amplify short fragments [193-454 base pairs [bp]] from coding exons [2-20] and screen for mutations using direct sequencing [DS]. Two mutations known to cause severe disease were identified in two samples. One was a coding mutation, c.2560C>T [p.Arg854X], and the second was found at a splice acceptor site, c.1327-2A>G. Polymerase chain reaction- and restriction fragment length polymorphism-based tests were designed for the rapid genotyping of the identified mutations. These tests can facilitate prenatal diagnosis and help in identifying carriers in families with the identified mutations

Detection of a novel mutation in the GAA gene in an Iranian child with glycogen storage disease type II

Glycogen storage disease II [GSDII or Pompe disease, OMIM # 232300] is an autosomal recessive hereditary lysosomal disorder. Mutations in the GAA gene usually lead to reduced acid alpha-glucosidase [acid maltase, GAA, OMIM [asterisk] 606800, EC 3.1.26.2] activity, which results in impaired degradation and subsequent accumulation of glycogen within lysosomes. We present an Iranian boy, who was diagnosed with GSDII based upon clinical and biochemical findings. A single adenine insertion [insA] was detected at codon 693 that leads to a predicted premature stop codon at codon 736 in the GAA gene. The parents were heterozygous for the same change. According to the human genome mutation database [www.hgmd.org] and lecture reviews, the detected change is a novel mutation. We suppose that the discovered insertion in the GAA gene might lead to a reduced activity of the gene product. This assumption is in agreement with biochemical and clinical signs in the patient

Homozygotic intronic GAA mutation in three siblings with late-onset Pompe's disease / Mutação homozigótica intrônica no gene GAA em três irmãos com doença de Pompe de início tardio

Pompe's disease (PD) is a metabolic myopathy caused by the accumulation of lysosomal glycogen, secondary to acid α-glucosidase (GAA) enzyme deficiency. Childhood and late-onset forms are described, differing by the age of onset and symptoms. In this study were analyzed affected siblings with Pompe's disease (PD) and their distinct clinical and pathological presentations. METHOD: Diagnosis was performed by the clinical presentation of limb-girdle dystrophies and respiratory compromise. Confirmatory diagnoses were conducted by muscle biopsy, GAA activity measurement and by GAA gene genotyping. RESULTS: The findings suggested muscular involvement due to GAA deficiency. GAA genotyping showed they are homozygous for the c.-32-3C>A mutation. CONCLUSION: Herein we reported a family where three out of five siblings were diagnosed with late-onset PD, although it is a rare metabolic disease inherited in an autossomal recessive manner. We emphasize the importance of including this presentation within the differential diagnoses of the limb-girdle dystrophies once enzyme replacement therapy is available.

A doença de Pompe (DP) é uma miopatia originada do acúmulo lisossomal de glicogênio, devido à deficiência da enzima α-glicosidase ácida (GAA), sendo descritas formas de inicio precoce e tardio. Neste estudo analisamos retrospectivamente o perfil clinico e patológico de 3 irmãos portadores de doença de Pompe de inicio tardio. MÉTODO: O diagnóstico foi realizado mediante apresentação clinica de distrofia de cinturas associado a comprometimento respiratório, sendo confirmado por biópsia muscular e análise da atividade e genotipagem da GAA. RESULTADOS: Os exames clínicos e laboratoriais demonstram envolvimento muscular devido à deficiência da GAA, com uma mutação c.-32-3C>A em homozigose. CONCLUSÃO: Relatamos os aspectos clínicos e laboratoriais de 3 irmãos afetados por doença de Pompe de início tardio. Enfatizamos a importância de incluir esta patologia no diagnóstico diferencial das distrofias de cinturas, uma vez que para esta patologia específica existe a possibilidade terapêutica através de reposição enzimática.

Regulation of MAL1+ gene expression encoding maltase in Schizosaccharomyces pombe by added inositol.

In this study, the effects of inositol addition on maltase activity and expression of MAL1+ gene encoding maltase in Schizosaccharomyces pombe were investigated. The maximum specific maltase activity was observed, when the concentration of inositol reached 6.0 microg/ml in the synthetic medium containing 2.0% glucose. At 1.0 microg/ml inositol concentration, the maltase activity continuously decreased, as initial glucose concentration was higher than 0.1%. mRNA encoding maltase and phosphatidylinositol (PI) content were higher in the cells grown in the synthetic medium with 6.0 microg/ml of inositol and 2.0% glucose than those with 1.0 microg/ml of inositol. These results demonstrated that higher inositol concentration in the synthetic medium could derepress MAL1+ gene expression in S. pombe and PI might be involved in derepression of MAL1+ gene expression in S. pombe probably by PI-type signalling pathway.