Sandhoff disease in the Turkish population

Clinical and Laboratory Profile of Gangliosidosis from Southern Part of India

Gangliosidoses are progressive neurodegenerative disorders caused by the deficiency of enzymes involved in the breakdown of glycosphingolipids. There are not much data about gangliosidosis in India; hence, this study was planned. The aim is to study the clinical, biochemical, and molecular profile of gangliosidosis. A retrospective chart review, in the pediatric neurology department from January 2015 to March 2020, was performed. Children diagnosed with Gangliosidosis were included. The disorder was confirmed by reduced activity of enzymes and/or pathogenic or likely pathogenic variants in associated genes. We assessed age at presentation, gender, parental consanguinity, clinical manifestations, neuroimaging findings, enzyme level, and pathogenic or likely pathogenic variants. Clinical data for 32 children with gangliosidosis were analyzed, which included 12 (37.5%) with GM1 gangliosidosis, 8 (25%) with Tay-Sachs disease (TSD), 11 (34.37%) with Sandhoff disease (SD), and 1 AB variant of GM2 gangliosidosis that occurs due to GM2 ganglioside activator protein deficiency. Twenty-four (75%) children were the offspring of consanguineous parents. Thirty-one (97%) had developmental delay. The median age at presentation was 15.5 months. Nine (28.12%) had seizures. Five children (41.6%) with GM1 gangliosidosis and two with SD had extensive Mongolian spots. Ten children with GM1 gangliosidosis (83.3%) had coarse facial features. Cherry red spot was found in 24 out of 32 children (75%). All children with GM1 gangliosidosis and none with TSD had hepato-splenomegaly. Two children (2/8; 25%) with TSD and seven (7/11; 63%) with SD had microcephaly. One child with SD had coarse facies and three did not have hepato-splenomegaly. Neuroimaging findings revealed bilateral thalamic involvement in 20 (62.5%) patients and periventricular hypomyelination in all cases. One child had a rare AB variant of GM2 gangliosidosis. GM2 Gangliosidoses are more common compared with GM1 variety. All of them had infantile onset except one child with TSD. Microcephaly can be present while usually megalencephaly is reported in the literature. The absence of hepato-splenomegaly does not rule out SD. Extensive Mongolian spots can be seen in GM2 gangliosidosis. AB variant of GM2 gangliosidosis should be considered when the enzyme is normal in the presence of strong clinical suspicion.

Clinical presentation and outcome in infantile Sandhoff disease: a case series of 25 patients from Iranian neurometabolic bioregistry with five novel mutations

BACKGROUND

Infantile Sandhoff disease (ISD) is a GM2 gangliosidosis that is classified as a lysosomal storage disorder. The most common symptoms of affected individuals at presentation are neurologic involvement. Here we report clinical course and demographic features in a case series of infantile Sandhoff disease. Enzymatically and some genetically proven cases of ISD were extracted from the Iranian Neurometabolic Registry (INMR) in Children's Medical Center, Iran, Tehran from December 2010 to December 2016.

RESULT

Twenty five cases of infantile SD (13 female, 12 male) were included in this study. The age range of patients was 9-24 months with a mean of 15.8 months. The consanguinity rate of parents affected families was about 80%. The mean age of patients at disease onset was 6.4 months and the mean age at diagnosis was 14 months. Patients were diagnosed with a mean delay of 7.8 months. Eleven of patients died due to aspiration pneumonia and intractable seizure. The most common features at presentation (92%) were developmental delay or regression in speech and cognitive domains. Cherry red spots were detected in 17 patients (68%). Organomegaly was detected only in two patients. Enzyme studies showed marked reductions of both Hexosaminidase A and B in all patients. HEXB gene mutation studies performed in eight patients identified 6 different mutations, which five of them were novel.

CONCLUSION

Infantile SD should be considered for each child presented with neurologic symptoms such as developmental delay and regression and cherry red spots in ophthalmic examination. Organomegaly is not a frequent clinical finding in infantile SD. Additionally; there are a genetic heterogenisity among Iranian patients.

Sandhoff Disease without Hepatosplenomegaly Due to Hexosaminidase B Gene Mutation

Sandhoff disease is a neurodegenerative disease caused due to deficiency of hexosaminidase (HEX) A and B. A 1-year-old male child presented with regression of milestones, exaggerated startle response, decreased vision, and seizures from 6 months of age. The child had coarse facies without hepatosplenomegaly. Serum levels of β hexosaminidase total (A + B) were low. Genetic testing for Sandhoff disease revealed a homozygous missense variant on HEXB gene. The case is presented to highlight that the absence of hepatosplenomegaly should not restrain in suspecting Sandhoff disease.

Sphingolipidoses in Turkey

During the last 5 years 2057 children under the age of 5 with various neurologic symptoms with the suspected diagnosis of lysosomal storage diseases were referred to our hospital from different universities and state hospitals. We were able to separate sphingolipidoses by lysosomal enzyme screening. A total of 300 patients (15%) with sphingolipidoses were diagnosed; there were deficiencies of arylsulfatase A [metachromatic leukodystrophy (MLD)] in 93 (31%), hexosaminidase [Sandhoff disease (SHD)] in 62 (20.7%), hexosaminidase A [Tay-Sachs disease (TSD)] in 15 (5%), beta-galactosidase (GM1 gangliosidosis) in 35 (11.7%), alpha-galactosidase (Fabry disease) in one (0.3%) cerebroside beta-galactosidase (Krabbe disease) in 65 (21.7%) and glucosylceramidase (Gaucher disease) in 29 (9.6%). SHD (20.7%), MLD (31%) and Krabbe disease (21.7%) were common. Prenatal enzymatic diagnosis was made in 70 at risk pregnancies, 64 for TSD and SHD, three for MLD and three for GM1 gangliosidosis by using chorionic villus biopsy in 54, cord blood samples in 12 and cultured amniotic fluid cells in four. Seventeen fetuses were found to be affected. We have calculated the relative frequency and minimum incidence of sphingolipidoses in Turkey. The combined incidence of sphingolipidoses is 4.615 per 100,000 live births. The calculated incidences are 1.43, 0.95, 1, 0.23, 0.54, 0.45, 0.015 per 100,000 live births for MLD, SHD, Krabbe, Gaucher, TSD, GM1 gangliosidosis and Fabry diseases, respectively. The real incidence, which covers all subtypes of this group of diseases, should be greater than this number. The results suggested that, as a group, sphingolipidoses are relatively common and represent an important health problem in Turkey and some rare autosomal recessive diseases of Turkey are due to 'founder effect' created by consanguineous marriages.

Infantile Sandhoff's disease: multivoxel magnetic resonance spectrosecopy findings

Sandhoff's disease is a rare, genetic lysosomal storage disease leading to delayed myelination or demyelination. Although neuroimaging findings in this disease have been reported previously, magnetic resonance spectroscopy findings have not been reported. In this report, we present magnetic resonance imaging and magnetic resonance spectrscopy features of two cases with Sandhoff's disease. Magnetic resonance spectroscopy revealed findings indicating widespread demyelination in both cases and neuroaxonal loss and anaerobic metabolism in the second case. Magnetic resonance spectroscopy could provide useful information in the explanation of the clinical picture of cases with Sandhoff's disease.

Characterization of two Turkish beta-hexosaminidase mutations causing Tay-Sachs disease

Two homoallelic mutations have recently been identified in the alpha-subunit of hexosaminidase A (EC 3.2.1.52) causing the infantile form of Tay-Sachs disease in Turkish patients. Both of these mutations, a 12 bp deletion (1096-1107 or 1098-1108 or 1099-1109) in exon 10 and a point mutation (G1362 to A, Gly454 to Asp) in exon 12, are located in the catalytic domain of the hexosaminidase alpha-chain. In order to determine whether these mutations affect the function of the catalytic domain or result in an instable protein, both mutant cDNAs were overexpressed in COS-1 cells. As judged by Western blotting, transfections of wild-type cDNA produced pro-alpha-chain and mature alpha-chain in parallel with a fivefold increase in cellular hexosaminidase activity using the synthetic substrate 4-methylumbelliferyl beta-N-acetylglucosamine 6-sulfate (MUGS). However, both mutants produced only pro-alpha-chains, although no mature form or detectable hexosaminidase activity towards two different synthetic substrates was observed. These data are consistent with the biochemical phenotype of infantile Tay-Sachs disease. We conclude that the overexpressed mutant pro-alpha-chains were misfolded and could not undergo further proteolytic processing to the active form of the enzyme in the lysosome.