CLINICAL CHARACTERISTICS: GLB1-related disorders comprise two phenotypically distinct lysosomal storage disorders: GM1 gangliosidosis and mucopolysaccharidosis type IVB (MPS IVB). GM1 gangliosidosis includes phenotypes that range from severe to mild.
Type I (infantile) begins before age one year; progressive central nervous system dysfunction leads to spasticity, deafness, blindness, and decerebrate rigidity. Life expectancy is two to three years. Type II can be subdivided into the late-infantile form and juvenile form. Type II, late-infantile form begins between ages one and three years; life expectancy is five to ten years. Type II, juvenile form begins between ages three and ten years with insidious plateauing of motor and cognitive development followed by slow regression. Type II may or may not include skeletal dysplasia. Type III begins in the second to third decade with extrapyramidal signs, gait disturbance, and cardiomyopathy; and can be misidentified as Parkinson disease. Intellectual impairment is common late in the disease; skeletal involvement includes short stature, kyphosis, and scoliosis of varying severity. MPS IVB is characterized by skeletal changes, including short stature and skeletal dysplasia. Affected children have no distinctive clinical findings at birth. The severe form is usually apparent between ages one and three years, and the attenuated form in late childhood or adolescence. In addition to skeletal involvement, significant morbidity can result from respiratory compromise, obstructive sleep apnea, valvular heart disease, hearing impairment, corneal clouding, and spinal cord compression. Intellect is normal unless spinal cord compression leads to central nervous system compromise. DIAGNOSIS/TESTING: The diagnosis of GLB1-related disorders is suspected in individuals with characteristic clinical, neuroimaging, radiographic, and biochemical findings. The diagnosis is confirmed by either deficiency of ß-galactosidase enzyme activity or biallelic pathogenic variants in GLB1. MANAGEMENT: Treatment of manifestations: Best provided by specialists in biochemical genetics, cardiology, orthopedics, and neurology and therapists knowledgeable about GLB1-related disorders; surgery is best performed in centers with surgeons and anesthesiologists experienced in the care of individuals with lysosomal storage disorders; occupational therapy to optimize activities of daily living (including adaptive equipment) and physical therapy to optimize gait and mobility (including orthotics and bracing); early and ongoing interventions to optimize educational and social outcomes. For those with GM1 gangliosidosis: Adequate nutrition to maintain growth; speech therapy to optimize oral motor skills; aggressive seizure control; routine management of risk of aspiration, risk of chronic urinary tract infection, and cardiac involvement; when disease is advanced: hospice services for supportive in-home care. Prevention of secondary complications: Anesthetic precautions to anticipate and manage complications relating to skeletal involvement and airway compromise; routine immunization; bacterial endocarditis prophylaxis in those with cardiac valvular disease. Surveillance: GM1 gangliosidosis: Routine monitoring of growth and nutrition. Assess yearly: quality of life including history and physical examination; seizure risk by a neurologist; cervical spine stability; and hip dislocation risk. Perform every one to three years: electrocardiogram and echocardiogram; eye examination. MPS IVB: Yearly: perform endurance tests to evaluate functional status of the cardiovascular, pulmonary, musculoskeletal, and nervous systems; assess lower extremities for malalignment, hips for dysplasia/subluxation, thoracolumbar spine for kyphosis, and cervical spine for instability; perform eye examination and audiogram. Perform electrocardiogram and echocardiogram every one to three years depending on disease course; assess for obstructive sleep apnea and restrictive lung disease; monitor nutritional status using MPS IVA-specific growth charts. Agents/circumstances to avoid: Psychotropic medications because of the risk of worsening neurologic disease; obesity in those with skeletal dysplasia GENETIC COUNSELING: GLB1-related disorders are inherited in an autosomal recessive manner. Each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk family members and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family have been identified.
Lei HL, etal., World J Pediatr. 2012 Nov;8(4):359-62. doi: 10.1007/s12519-012-0382-0. Epub 2012 Nov 15.
BACKGROUND: This paper aims to report GLB1 activities and mutation analysis of three patients from the mainland of China, one with Morquio B disease and two with GM1 gangliosidosis. METHODS: GLB1 activity and GLB1
nt-weight:700;'>GLB1 gene mutation were analyzed in the three patients who were clinically suspected of having Morquio B disease or GM1 gangliosidosis. Novel mutations were analyzed by aligning GLB1 homologs, 100 control chromosomes, and the PolyPhen-2 tool. RESULTS: The enzymatic activity of GLB1 was found to be 5.03, 4.20, and 4.50 nmol/h/mg in the three patients, respectively. Patient 1 was a compound heterozygote for p.[Arg148Cys] and p.[Tyr485Cys] mutations in the GLB1 gene. Patient 2 was a compound heterozygote for p.[Tyr270Phe] and p.[Leu337Pro] mutations. Patient 3 was a homozygote for p.[Asp448Val] mutation. Three mutations (p.[Tyr485Cys], p.[Tyr270Phe] and p.[Leu337Pro]) were novel variants and were predicted to damage GLB1 function. CONCLUSIONS: The enzymatic activity and related gene analysis of beta-galactosidase should be performed in clinically suspected individuals to confirm diagnosis. The three novel mutations, p.[Tyr485Cys], p.[Tyr270Phe], and p.[Leu337Pro], are thought to be disease-causing mutations.
GM1-gangliosidosis and Morquio B disease are lysosomal storage disorders caused by beta-galactosidase deficiency attributable to mutations in the GLB1 gene. On reaching the endosomal-lysosomal compartment, the beta-galactosidase protein associates with the prote
ctive protein/cathepsin A (PPCA) and neuraminidase proteins to form the lysosomal multienzyme complex (LMC). The correct interaction of these proteins in the complex is essential for their activity. More than 100 mutations have been described in GM1-gangliosidosis and Morquio B patients, but few have been further characterized. We expressed 12 mutations suspected to be pathogenic, one known polymorphic change (p.S532G), and a variant described as either a pathogenic or a polymorphic change (p.R521C). Ten of them had not been expressed before. The expression analysis confirmed the pathogenicity of the 12 mutations, whereas the relatively high activity of p.S532G is consistent with its definition as a polymorphism. The results for p.R521C suggest that this change is a low-penetrant disease-causing allele. Furthermore, the effect of these beta-galactosidase changes on the LMC was also studied by coimmunoprecipitations and Western blotting. The alteration of neuraminidase and PPCA patterns in several of the Western blotting analyses performed on patient protein extracts indicated that the LMC is affected in at least some GM1-gangliosidosis and Morquio B patients.
GM1 gangliosidosis is a lysosomal storage disorder caused by the absence or reduction of lysosomal beta-galactosidase activity because of mutations in the GLB1 gene. Three major clinical forms have been established: type I (infantile), type II (late infantile/ju
venile) and type III (adult). A mutational analysis was performed in 19 patients with GM1 gangliosidosis from South America, mainly from Argentina. Two of them were of Gypsy origin. Main clinical findings of the patients are presented. All 38 mutant alleles were identified: of the 22 different mutations found, 14 mutations are described here for the first time. Among the novel mutations, five deletions were found. Four of them are relatively small (c.435_440delTCT, c.845_846delC, c.1131_1145del15 and c.1706_1707delC), while the other one is a deletion of 1529 nucleotides that includes exon 5 and is caused by an unequal crossover between intronic Alu sequences. All the described patients with GM1 gangliosidosis were affected by the infantile form, except for four unrelated patients classified as type II, III, and II/III (two cases). The two type II/III patients bore the previously described p.R201H mutation, while the adult patient bore the new p.L155R. The juvenile patient bore two novel mutations: p.S434L and p.G554E. The two Gypsy patients are homozygous for the p.R59H mutation as are all Gypsy patients previously genotyped.
BACKGROUND: Beta-galactosidase-1 (GLB1) is a lysosomal hydrolase that is responsible for breaking down specific glycoconjugates, particularly GM1 (monosialotetrahexosylganglioside). Pathogenic variants in GLB1 cau
se two different lysosomal storage disorders: GM1 gangliosidosis and mucopolysaccharidosis type IVB. In GM1 gangliosidosis, decreased β-galactosidase-1 enzymatic activity leads to the accumulation of GM1 gangliosides, predominantly within the CNS. We present a 22-month-old proband with GM1 gangliosidosis type II (late-infantile form) in whom a novel homozygous in-frame deletion (c.1468_1470delAAC, p.Asn490del) in GLB1 was detected. METHODS: We used an experimental protein structure of β-galactosidase-1 to generate a model of the p.Asn490del mutant and performed molecular dynamic simulations to determine whether this mutation leads to altered ligand positioning compared to the wild-type protein. In addition, residual mutant enzyme activity in patient leukocytes was evaluated using a fluorometric assay. RESULTS: Molecular dynamics simulations showed the deletion to alter the catalytic site leading to misalignment of the catalytic residues and loss of collective motion within the model. We predict this misalignment will lead to impaired catalysis of β-galactosidase-1 substrates. Enzyme assays confirmed diminished GLB1 enzymatic activity (~3% of normal activity) in the proband. CONCLUSIONS: We have described a novel, pathogenic in-frame deletion of GLB1 in a patient with GM1 gangliosidosis type II.
GM1-gangliosidosis and Morquio B disease are rare lysosomal storage disorders caused by beta-galactosidase deficiency due to mutations in the GLB1 gene. Three major clinical forms of GM1-gangliosidosis have been established on the basis of age of onset and sev
erity of symptoms: infantile, late infantile/juvenile, and adult. We performed mutation analysis on 30 GM1-gangliosidosis and five Morquio B patients, mainly of Spanish origin, and all the causative mutations were identified. Thirty different mutations were found, 21 of which were novel. With the exception of two adults and one juvenile patient, all the GM1-gangliosidosis patients were affected by the infantile form. Clinical findings are presented for all patients. We report the association of the novel mutations p.T420K and p.L264S with the adult form and the juvenile form, respectively. In addition, the novel mutation p.Y83C was associated with Morquio B disease. Among the 30 GM1-gangliosidosis patients, 6 were of Gypsy origin (Roma). Moreover, those six Gypsy patients shared not only the same mutation (p.R59H) but also a common haplotype. This observation indicates a possible founder effect in this group and suggests that screening of the p.R59H mutation may be appropriate in GM1-gangliosidosis patients of Gypsy origin. This is the first exhaustive mutational analysis performed in a large group of Iberian GM1-gangliosidosis and Morquio B patients.
