OBJECTIVE: To detect potential mutations of HEXB gene in an infant with Sandhoff disease (SD). METHODS: Genomic DNA was extracted from peripheral blood sample of the infant. All coding exons (exons 1 to 14) and splicing sites of the HEXB gene were subjected to PCR amplification and direct sequencing.PubMed Protein BLAST system was employed to analyze cross-species conservation of the mutant amino acid. PubMed BLAST CD-search was performed to identify functional domains destroyed by thecandidate mutations. Impact of the mutations was analyzed with software including PolyPhen-2, Mutation Taster and SIFT. Whole-exome sequencing was carried out to identify additional mutations. RESULTS: The infant was found to carry compound heterozygous mutations c.1652G>A(p.Cys551Tyr) and c.1389C>G (p.Tyr463*) of the HEXB gene. The c.1389C>G (p.Tyr463*) mutation may lead to destruction of two functional domains in β subunit of the Hex protein. The c.1652G>A(p.Cys551Tyr) mutation, unreported previously,was predicted to be probably damaging by Bioinformatic analysis. CONCLUSION Compound heterozygous mutations c.1652G>A(p.Cys551Tyr) and c.1389C>G (p.Tyr463*) in the HEXB gene probably underlie the disease in this patient.
DNA Mutational Analysis ; Exons ; Heterozygote ; Humans ; Infant ; Mutation ; Polymerase Chain Reaction ; Sandhoff Disease ; genetics ; beta-Hexosaminidase beta Chain ; genetics

OBJECTIVETo investigate the phenotype and genotype of a Chinese boy and his family affected by infantile Sandhoff disease.

METHODSThe proband, a boy, was the first child born to a non-consanguineous couple. He showed startle reaction after birth and progressive psychomotor regression from the age of 8 months. From the age of 16 months, he presented seizures. When he was admitted at 17 months old, severe mental retardation and weakness were observed. Fundus examination revealed bilateral cherry-red spots in the macula and optic atrophy. Cranial MRI revealed abnormal signals in the thalamus, basal ganglia and white matter. Enzymatic assay and genetic testing were performed for the diagnosis. His mother visited us at 18 weeks of pregnancy seeking for prenatal diagnosis. HEXB gene diagnosis to the fetus was performed by direct sequencing.

RESULTSSignificant deficient total β-hexosaminidase (A and B) activity in peripheral leucocytes of the patient (0.0 nmol/h/mg compared with normal control, 41.9 to 135.1 nmol/h/mg) supported the diagnosis of Sandhoff disease. On his HEXB gene, two mutations were found. c.1645G-A (p.G549R) was novel. c.IVS7-48T was a reported mutation. Now, the patient was 2 years and 3 months old, with progressive general failure, severe epilepsy, blindness and hypermyotonia. Subsequently, the mother visited us at 18 weeks of pregnancy seeking for prenatal diagnosis. HEXB gene analysis of the amniocytes was performed by direct sequencing. Both of the two mutations were not detected from cultured amniocytes. The result revealed that the fetus was not affected by Sandhoff disease. A healthy girl, the sibling of the proband, was born in term. Postnatal enzyme analysis and genetic analysis of the cord blood cells confirmed the prenatal diagnosis.

CONCLUSIONOne novel mutation on HEXB gene was identified. Prenatal diagnosis to the fetus of this family was performed by amniocytes gene analysis.

Adult ; Amniotic Fluid ; cytology ; Child, Preschool ; DNA Mutational Analysis ; Female ; Genetic Testing ; Humans ; Male ; Mutation ; Pregnancy ; Prenatal Diagnosis ; Sandhoff Disease ; diagnosis ; genetics ; beta-Hexosaminidase beta Chain ; genetics

OBJECTIVETo explore the clinical features and molecular mutation of HEXB gene in a case with juvenile Sandhoff disease.

METHODWe retrospectively reviewed the clinical, neuroimaging and biochemical findings in this Chinese child with juvenile Sandhoff disease. Hexosaminidase A and hexosaminidase A & B activities were measured in blood leukocytes by fluorometric assay. HEXB gene molecular analysis was performed by PCR and direct sequencing.

RESULTThe 9-year-old boy was admitted for psychomotor regression. He presented slowly progressive gait disorder and dysarthria during the last three years. Cranial MRI revealed a marked cerebellar atrophy with normal intensity in the thalamus and basal ganglia. Brain MRS showed normal in the thalamus and basal ganglia. Hexosaminidase A was 69.5 (mg·h) [normal controls 150-360 nmol/(mg·h)], hexosaminidase A & B activity was 119 nmol/(mg·h)[normal controls 600-3 500 nmol/(mg·h)], confirming the diagnosis of Sandhoff disease. The patient was a compound heterozygote for a novel deletion mutation c.1404delT (p. P468P fsX62) and a reported mutation c.1509-26G>A.

CONCLUSIONThe clinical features of juvenile Sandhoff disease include ataxia, dysarthria and cerebellar atrophy. The enzyme assay and molecular analysis of HEXB gene can confirm the diagnosis of Sandhoff disease. The novel mutation c.1404delT(p. P468P fsX62) is a disease-related mutation.

Brain ; diagnostic imaging ; pathology ; Cerebellar Ataxia ; diagnosis ; enzymology ; genetics ; Child ; DNA Mutational Analysis ; Heterozygote ; Hexosaminidase A ; blood ; metabolism ; Hexosaminidase B ; blood ; metabolism ; Humans ; Leukocytes ; enzymology ; Magnetic Resonance Imaging ; Male ; Mutation ; Radiography ; Retrospective Studies ; Sandhoff Disease ; diagnosis ; enzymology ; genetics ; beta-Hexosaminidase beta Chain ; genetics