Identification of four novel mutations in the alpha glucosidase gene in five Italian patients with infantile onset glycogen storage disease type II

Acid Sphingomyelinase Deficiency: A Clinical and Immunological Perspective

Acid sphingomyelinase deficiency (ASMD) is a lysosomal storage disease caused by deficient activity of acid sphingomyelinase (ASM) enzyme, leading to the accumulation of varying degrees of sphingomyelin. Lipid storage leads to foam cell infiltration in tissues, and clinical features including hepatosplenomegaly, pulmonary insufficiency and in some cases central nervous system involvement. ASM enzyme replacement therapy is currently in clinical trial being the first treatment addressing the underlying pathology of the disease. Therefore, presently, it is critical to better comprehend ASMD to improve its diagnose and monitoring. Lung disease, including recurrent pulmonary infections, are common in ASMD patients. Along with lung disease, several immune system alterations have been described both in patients and in ASMD animal models, thus highlighting the role of ASM enzyme in the immune system. In this review, we summarized the pivotal roles of ASM in several immune system cells namely on macrophages, Natural Killer (NK) cells, NKT cells, B cells and T cells. In addition, an overview of diagnose, monitoring and treatment of ASMD is provided highlighting the new enzyme replacement therapy available.

Late onset Pompe Disease in India - Beyond the Caucasian phenotype

We evaluated the clinical histories, motor and pulmonary functions, cardiac phenotypes and GAA genotypes of an Indian cohort of twenty patients with late onset Pompe disease (LOPD) in this multi-centre study. A mean age at onset of symptoms and diagnosis of 9.9 ± 9.7 years and 15.8 ± 12.1 years respectively was identified. All patients had lower extremity limb-girdle muscle weakness. Seven required ventilatory support and seven used mobility assists. Of the four who used both assists, two received ventilatory support prior to wheelchair use. Cardiac involvement was seen in eight patients with various combinations of left ventricular hypertrophy, tricuspid regurgitation, cardiomyopathy, dilated ventricles with biventricular dysfunction and aortic regurgitation. Amongst 20 biochemically diagnosed patients (low residual GAA enzyme activity) GAA genotypes of 19 patients identified homozygous variants in eight and compound heterozygous in 11: 27 missense, 3 nonsense, 2 initiator codon, 3 splice site and one deletion. Nine variants in 7 patients were novel. The leaky Caucasian, splice site LOPD variant, c.-32-13T>G mutation was absent. This first study from India provides an insight into a more severe LOPD phenotype with earlier disease onset at 9.9 years compared to 33.3 years in Caucasian patients, and cardiac involvement more than previously reported. The need for improvement in awareness and diagnosis of LOPD in India is highlighted.

Clinical and Molecular Characterization of Infantile-Onset Pompe Disease in Mainland Chinese Patients: Identification of Two Common Mutations

AIMS

We sought to understand the clinical course and molecular defects of infantile-onset Pompe disease (IOPD) among mainland Chinese patients.

MATERIALS AND METHODS

Twenty-five Chinese patients with IOPD were enrolled and clinical data were retrospectively reviewed. The entire coding region of the GAA gene was amplified by polymerase chain reaction and analyzed by direct sequencing.

RESULTS

The median age at symptom onset was 3.4 months (range: 1.0-7.1 months) and 4.9 months (range: 2.7-8.3 months) at diagnosis. Only one patient received enzyme replacement therapy (ERT) and this child survived beyond the age of 2 years. Of the 24 patients not receiving ERT, all, but one patient, died at a median age of 8.3 months (range: 4.0-12.2 months). Thirteen novel and two common GAA mutations were identified in this study. The allelic frequency of c.2662G > T (p.Glu888X) was 23.1% in northern Chinese patients and 4.2% in southern Chinese patients, whereas the allelic frequency of c.1935C > A (p.Asp645Glu) was 20.8% in southern and 3.8% in northern Chinese patients.

CONCLUSIONS

We identified the most common mutations in southern and northern Chinese patients with IOPD.

Alkaptonuria and Pompe disease in one patient: metabolic and molecular analysis

Pompe disease is characterised by deficiency of acid α-glucosidase that results in abnormal glycogen deposition in the muscles. Alkaptonuria is caused by a defect in the enzyme homogentisate 1,2-dioxygenase with subsequent accumulation of homogentisic acid. We report the case of a 6-year-old boy diagnosed with Pompe disease and alkaptonuria. Urine organic acids and α-glucosidase were measured. Homogentisate 1,2-dioxygenase (HGO) and acid alpha-glucosidase (GAA) genes were sequenced by Sanger DNA sequencing. The level of α-glucosidase in white blood cells was markedly decreased (4 nm/mg) while the level of homogentisic acid was markedly increased (15 027 mmol/mol creatine). GAA sequencing detected two heterozygous GAA mutations (C.670C>T and C.1064T>C) while HGO sequencing revealed three polymorphisms in exons 4, 5 and 6, respectively. To the best of our knowledge, this is the first reported instance of Pompe disease and alkaptonuria occurring in the same individual.

A nonsense mutation in the acid α-glucosidase gene causes Pompe disease in Finnish and Swedish Lapphunds

Pompe disease is a recessively inherited and often fatal disorder caused by the deficiency of acid α-glucosidase, an enzyme encoded by the GAA gene and needed to break down glycogen in lysosomes. This glycogen storage disease type II has been reported also in Swedish Lapphund dogs. Here we describe the genetic defect in canine Pompe disease and show that three related breeds from Scandinavia carry the same mutation. The affected dogs are homozygous for the GAA c.2237G>A mutation leading to a premature stop codon at amino acid position 746. The corresponding mutation has previously been reported in humans and causes infantile Pompe disease in combination with a second fully deleterious mutation. The affected dogs from both the Finnish as well as the Swedish breed mimic infantile-onset Pompe disease genetically, but also clinico-pathologically. Therefore this canine model provides a valuable tool for preclinical studies aimed at the development of gene therapy in Pompe disease.

Functional analysis of variant lysosomal acid glycosidases of Anderson-Fabry and Pompe disease in a human embryonic kidney epithelial cell line (HEK 293 T)

The functional significance of missense mutations in genes encoding acid glycosidases of lysosomal storage disorders (LSDs) is not always clear. Here we describe a method of investigating functional properties of variant enzymes in vitro using a human embryonic kidney epithelial cell line. Site-directed mutagenesis was performed on the parental plasmids containing cDNA encoding for alpha-galactosidase A (α-Gal A) and acid maltase (α-Glu) to prepare plasmids encoding relevant point mutations. Mutant plasmids were transfected into HEK 293 T cells, and transient over-expression of variant enzymes was measured after 3 days. We have illustrated the method by examining enzymatic activities of four unknown α-Gal A and one α-Glu variants identified in our patients with Anderson-Fabry disease and Pompe diseases respectively. Comparison with control variants known to be either pathogenic or non-pathogenic together with over-expression of wild-type enzyme allowed determination of the pathogenicity of the mutation. One leader sequence novel variant of α-Gal A (p.A15T) was shown not to significantly reduce enzyme activity, whereas three other novel α-Gal A variants (p.D93Y, p.L372P and p.T410I) were shown to be pathogenic as they resulted in significant reduction of enzyme activity. A novel α-Glu variant (p.L72R) was shown to be pathogenic as this significantly reduced enzyme activity. Certain acid glycosidase variants that have been described in association with late-onset LSDs and which are known to have variable residual plasma and leukocyte enzyme activity in patients appear to show intermediate to low enzyme activity (p.N215S and p.Q279E α-Gal A respectively) in the over-expression system.

Two new missense mutations of GAA in late onset glycogen storage disease type II

Glycogen storage disease type II (GSD II) is an autosomal recessive disorder resulting from a deficiency of acid alpha-glucosidase (GAA, or acid maltase). In this study, we aimed to characterize phenotype and genotype in three patients with late onset GSD II in Korea. Clinically, all of our patients showed typical features of late onset GSD II with the reduced GAA enzyme activities. The respiratory difficulty preceding ambulatory failure seems to be one of the most remarkable clinical features characterizing late onset GSD II. By direct sequence analysis of PCR-amplified genomic DNA obtained from patients' skeletal muscle or peripheral leukocytes, we identified four missense mutations. Two of them (p.266Pro>Ser and p.439Met>Lys) were new missense mutations causing late onset GSD II, which had not been reported elsewhere before. One of them (p.439Met>Lys) was found in two alleles from each patient, suggesting it could be a recurrent mutation among Korean population.

Pompe disease (glycogen storage disease type II) in Argentineans: clinical manifestations and identification of 9 novel mutations

Pompe disease is an autosomal recessive disorder caused by a deficiency in 1,4-alpha-glucosidase (EC.3.2.1.3), the enzyme required to hydrolyze lysosomal glycogen to glucose. While previous studies have focused on Pompe patients from Europe, the United States, and Taiwan, we have analyzed a group of South American Pompe patients to better understand the molecular basis of their disease. From 14 Argentinean patients diagnosed with either infantile or late-onset disease, we identified 14 distinct mutations in the acid alpha-glucosidase (GAA) gene including nine novel variants (c.236_246del, c.377G>A, c.1099T>C, c.1397T>G, c.1755-1G>A, c.1802C>G, c.1978C>T, c.2281delGinsAT, and c.2608C>T). Three different families displayed the c.377G>A allelic variant, suggesting a higher frequency among a subset of Argentineans. Comparison of patients with similar or identical variations in the GAA gene highlights the phenotypic diversity of late-onset disease and supports a role for other genetic and environmental factors in disease presentation.

Mutation profile of theGAA gene in 40 Italian patients with late onset glycogen storage disease type II

Glycogen storage disease type II (GSDII) is a recessively inherited disorder due to the deficiency of acid alpha-glucosidase (GAA) that results in impaired glycogen degradation and its accumulation in the lysosomes. We report here the complete molecular analysis of the GAA gene performed on 40 Italian patients with late onset GSDII. Twelve novel alleles have been identified: missense mutations were functionally characterized by enzyme activity and protein processing in a human GAA-deficient cell line while splicing mutations were studied by RT-PCR and in silico analysis. A complex allele was also identified carrying three different alterations in cis. The c.-32-13T > G was the most frequent mutation, present as compound heterozygote in 85% of the patients (allele frequency 42.3%), as described in other late onset GSDII Caucasian populations. Interestingly, the c.-32-13T > G was associated with the c.2237G > A (p.W746X) in nine of the 40 patients. Genotype-phenotype correlations are discussed with particular emphasis on the subgroup carrying the c.-32-13T > G/c.2237G > A genotype.

Glycogenosis type II: identification and expression of three novel mutations in the acid alpha-glucosidase gene causing the infantile form of the disease

Glycogenosis type II (GSDII) is an autosomal recessive disorder due to the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). We identified three novel point mutations, C399A, T1064C, and C2104T, in three unrelated Italian patients with the infantile form of the disease. The C399A mutation was present in homozygosity in proband 1. The C >A transition introduces a premature stop signal in exon 2 resulting in no enzyme production that is correlated with the severe clinical phenotype in this patient. The other two nucleotide changes were missense mutations. The T1064C mutation, which changes Leu in position 355 into Pro, was carried in homozygosity by proband 2. The C2104T nucleotide change, which substitutes Arg 702 into Cys, was present in proband 3 in combination with a known severe mutation DeltaI17-18. The in vitro expression in COS-1 cells of T1064C and C2104T constructs demonstrated no enzymatic activity with respect to the negative control cells. Western blot analysis revealed that both T1064C and C2104T mutant proteins produced in COS-1 cells migrated in SDS-PAGE as the GAA inactive precursor of 110kDa. Immunofluorescence detection of mutant alpha-glucosidases showed enzyme localization primarily in the ER-Golgi compartment, suggesting that T1064C and C2104T mutations could affect the normal processing and stability of the enzyme. In vitro studies demonstrated that the same degree of deficiency in T1064C and C2104T mutations, which is in contrast with patient phenotype. A better correlation was observed with the in vivo studies since proband 2, with a less severe phenotype, presented with low residual enzyme activity while in proband 3, with a classic severe infantile onset GSDII, fibroblast enzyme activity was completely absent.