Four novel mutations in patients from the Middle East with the infantile form of GM1-gangliosidosis

The pharmacological chaperone N-n-butyl-deoxygalactonojirimycin enhances β-galactosidase processing and activity in fibroblasts of a patient with infantile GM1-gangliosidosis

GM1-gangliosidosis, a lysosomal storage disorder, is associated with ~ 161 missense variants in the GLB1 gene. Affected patients present with β-galactosidase (β-Gal) deficiency in lysosomes. Loss of function in ER-retained misfolded enzymes with missense variants is often due to subcellular mislocalization. Deoxygalactonojirimycin (DGJ) and its derivatives are pharmaceutical chaperones that directly bind to mutated β-Gal in the ER promoting its folding and trafficking to lysosomes and thus enhancing its activity. An Emirati child has been diagnosed with infantile GM1-gangliosidosis carrying the reported p.D151Y variant. We show that p.D151Y β-Gal in patient's fibroblasts retained < 1% residual activity due to impaired processing and trafficking. The amino acid substitution significantly affected the enzyme conformation; however, p.D151Y β-Gal was amenable for partial rescue in the presence of glycerol or at reduced temperature where activity was enhanced with ~ 2.3 and 7 folds, respectively. The butyl (NB-DGJ) and nonyl (NN-DGJ) derivatives of DGJ chaperoning function were evaluated by measuring their IC₅₀s and ability to stabilize the wild-type β-Gal against thermal degradation. Although NN-DGJ showed higher affinity to β-Gal, it did not show a significant enhancement in p.D151Y β-Gal activity. However, NB-DGJ promoted p.D151Y β-Gal maturation and enhanced its activity up to ~ 4.5% of control activity within 24 h which was significantly increased to ~ 10% within 6 days. NB-DGJ enhancement effect was sustained over 3 days after washing it out from culture media. We therefore conclude that NB-DGJ might be a promising therapeutic chemical chaperone in infantile GM1 amenable variants and therefore warrants further analysis for its clinical applications.

Recurrent and novel GLB1 mutations in India

GM1 gangliosidosis is a lysosomal storage disorder caused by mutations in the GLB1 gene, leading to the deficiency of the enzyme β-d-galactosidase. In this study, we report molecular findings in 50 Asian Indian families with GM1 gangliosidosis. We sequenced all the exons and flanking intronic sequences of GLB1 gene. We identified 33 different mutations (20 novel and 13 previously reported). The novel mutations include 12 missense (p.M1?, p.E129Q, p.G134R, p.L236P, p.G262E, p.L297F, p.Y331C, p.G414V, p.K493N, p.L514P, p.P597L, p.T600I), four splicing (c.246-2A>G, c.397-2A>G, c.552+1G>T, c.956-2A>G), three indels (p.R22Qfs*8, p.L24Cfs*47, p.I489Qfs*4) and one nonsense mutation (p.Q452*). Most common mutations identified in this study were c.75+2InsT (14%) and p.L337P (10%). Known mutations accounted for 67% of allele frequency in our cohort of patients, suggesting that these mutations in GLB1 are recurrent across different populations. Twenty three mutations were localized in the TIM barrel domain, β-domain 1 and β-domain 2. In silico sequence and structure analysis of GLB1 reveal that all the novel mutations affect the function and structure of the protein. We hereby report on the largest series of patients with GM1 gangliosidosis and the first from India.

Prevalence and Novel Mutations of Lysosomal Storage Disorders in United Arab Emirates : LSD in UAE

Lysosomal storage disorders (LSD) are rare entities of recessive inheritance. The presence of a "founder" mutation in isolated communities with a high degree of consanguinity (e.g., tribes in the Middle East North Africa, MENA, region) is expected to lead to unusually high disease prevalence. The primary aim of this study was to estimate the prevalence of LSD and report their mutation spectrum in UAE. Between 1995 and 2010, 119 patients were diagnosed with LSD (65 Emiratis and 54 non-Emiratis). Genotyping was performed in 59 (50 %) patients (39 Emirati from 17 families and 20 non-Emiratis from 17 families). The prevalence of LSD in Emiratis was 26.9/100,000 live births. Sphingolipidoses were relatively common (9.8/100,000), with GM1-gangliosidosis being the most prevalent (4.7/100,000). Of the Mucopolysaccharidoses VI, IVA and IIIB were the predominant subtypes (5.5/100,000). Compared to Western countries, the prevalence of fucosidosis, Batten disease, and α-mannosidosis was 40-, sevenfold, and fourfold higher in UAE, respectively. The prevalence of Pompe disease (2.7/100,000) was similar to The Netherlands, but only the infantile subtype was found in UAE. Sixteen distinct LSD mutations were identified in 39 Emirati patients. Eight (50 %) mutations were reported only in Emirati, of which three were novel [c.1694G>T in the NAGLU gene, c.1336 C>T in the GLB1 gene, and homozygous deletions in the CLN3 gene]. Twenty-seven (42 %) patients were clustered in five of the 70 Emirati tribes. These findings highlight the need for tribal-based premarital testing and genetic counseling.

Identification of mutations underlying 20 inborn errors of metabolism in the United Arab Emirates population

Inborn errors of metabolism (IEM) are frequently encountered by physicians in the United Arab Emirates (UAE). However, the mutations underlying a large number of these disorders have not yet been determined. Therefore, the objective of this study was to identify the mutations underlying a number of IEM disorders among UAE residents from both national and expatriate families. A case series of patients from 34 families attending the metabolic clinic at Tawam Hospital were clinically evaluated, and molecular testing was carried out to determine their causative mutations. The mutation analysis was carried out at molecular genetics diagnostic laboratories. Thirty-eight mutations have been identified as responsible for twenty IEM disorders, including in the metabolism of amino acids, lipids, steroids, metal transport and mitochondrial energy metabolism, and lysosomal storage disorders. Nine of the identified mutations are novel, including two missense mutations, three premature stop codons and four splice site mutations. Mutation analysis of IEM disorders in the UAE population has an important impact on molecular diagnosis and genetic counseling for families affected by these disorders.

Mutations of a country: a mutation review of single gene disorders in the United Arab Emirates (UAE)

The United Arab Emirates inhabitants are ethnically diverse, with ancestries from Arabia, Persia, Baluchistan, and Africa. However, the majority of the current five million inhabitants are expatriates from the Asian subcontinent, Middle Eastern, African, and European countries. Consanguineous marriages within most UAE subpopulations are still the norm, leading to the formation of isolates and higher frequencies of recessive conditions. The UAE is ranked sixth in terms of prevalence of birth defects, with more than 270 genetic disorders reported in the national population. The UAE has high frequencies of blood disorders including thalassemias, sickle cell disease, and G6PD. In addition, certain genetic conditions are relatively common including cystic fibrosis, Joubert, and Meckel syndromes. Furthermore, numerous rare congenital malformations and metabolic disorders have been reported. We review the single gene disorders that have been studied at the molecular level in the UAE (which currently stand at 76) and compile the mutations found. Several novel (p.S2439fs) mutations have been reported including c.7317delA in NF1, c.5C>T (p.A2V) in DKC1, c.1766T>A (p.I589N) in TP63, and c.2117G>T (p.R706L) in VLDLR. We hope that this review will form the basis to establish a UAE mutations database and serve as a model for the collection of mutations of a country.

Phenotype determining alleles in GM1 gangliosidosis patients bearing novel GLB1 mutations

GM1 gangliosidosis manifests with progressive psychomotor deterioration and dysostosis of infantile, juvenile, or adult onset, caused by alterations in the structural gene coding for lysosomal acid beta-galactosidase (GLB1). In addition, allelic variants of this gene can result in Morquio B disease (MBD), a phenotype with dysostosis multiplex and entire lack of neurologic involvement. More than 100 sequence alterations in the GLB1 gene have been identified so far, but only few could be proven to be predictive for one of the GM1 gangliosidosis subtypes or MBD. We performed genotype analyses in 16 GM1 gangliosidosis patients of all phenotypes and detected 28 different genetic lesions. Among these, p.I55FfsX16, p.W65X, p.F107L, p.H112P, p.C127Y, p.W161X, p.I181K, p.C230R, p.W273X, p.R299VfsX5, p.A301V, p.F357L, p.K359KfsX23, p.L389P, p.D448V, p.D448GfsX8, and the intronic mutation IVS6-8A>G have not been published so far. Due to their occurrence in homozygous patients, four mutations could be correlated to a distinct GM1 gangliosidosis phenotype. Furthermore, the missense mutations from heteroallelic patients and three artificial nonsense mutations were characterized by overexpression in COS-1 cells, and the subcellular localization of the mutant proteins in fibroblasts was assessed. The phenotype specificity of 10 alleles can be proposed on the basis of our results and previous data.

GM1 gangliosidosis: review of clinical, molecular, and therapeutic aspects

GM(1) gangliosidosis is a lysosomal storage disorder due to deficiency of the beta-galactosidase enzyme. This deficiency results in accumulation of GM(1) gangliosides and related glycoconjugates in the lysosomes leading to lysosomal swelling, cellular damage, and organ dysfunction. The disease is lethal in the infantile and juvenile forms. To date, up to 102 mutations distributed along the beta-galactosidase gene (GLB1) have been reported. This review gives an overview of the clinical and molecular findings in patients with GM(1) gangliosidosis. Furthermore, it describes therapeutic approaches which are currently under investigation in animal models of the disease.

Brain proton magnetic resonance spectroscopy and neuromuscular pathology in a patient with GM1 gangliosidosis

The authors report the clinical, neuroradiologic, and neuromuscular pathological findings in a patient with GM1 gangliosidosis. The proton magnetic resonance spectroscopy, previously reported in a single patient with GM1 gangliosidosis, detected a mild reduction of N-acetylaspartate, consistent with relative paucity of axons and neurons and increased levels of myoinositol suggestive of gliotic white matter changes along with the accumulation of an additional compound that could represent either guanidinoacetate or Gal beta 1-6Gal beta 1-4)GlcNAc, an oligosaccharide previously isolated from the urine of GM1 gangliosidosis patients. Although these findings will have to be further confirmed in more patients with GM1 gangliosidosis, they suggest that proton magnetic resonance spectroscopy may provide useful end points to assess the efficacy of novel treatments that could soon become clinically available. Histologically, no significant alterations were found in axons, but there was evidence of redundant and inappropriately folded myelin, which is a feature attributed to disturbed axon-glial interactions.

Gangliosides as apoptotic signals in ER stress response

Renewed attention has been given lately to gangliosides and to their function as intracellular messengers of the adaptive responses to stress. Gangliosides are vital components of cell membranes; therefore, deleterious consequences can result from changes in their chemical composition and concentration, that is, membrane dynamics and structure can be altered as can the behavior of other membrane proteins. The importance of gangliosides in human health is evident in neurodegenerative diseases associated with defects in their degradation. As key modulators of intracellular calcium flux, gangliosides are involved in cellular processes downstream of calcium signaling. In this review, we focus on the effect of ganglioside accumulation on the endoplasmic reticulum calcium homeostasis and on the integrity of the mitochondrial membranes. We discuss how these events elicit an apoptotic program that ultimately leads to cell death. Owing to interorganelle crosstalk, these events are not necessarily self-contained, and gangliosides may serve as the common factor.