Genetic cause of a juvenile form of tay‐sachs disease in a lebanese child

Abstract
Abnormality in the β‐hexosaminidase α gene underlying the clinical phenotype of a Lebanese patient with a juvenile form of Tay‐Sachs disease has been studied. Clinical features were progressive spasticity, ataxia, and cognitive decline. The protein coding sequence of several β‐hexosaminidase α‐chain complementary DNAs isolated by polymerase chain reaction was completely normal except for a G‐to‐A transition at nucleotide position 1511 within exon 13, which resulted in substitution of the normal arginine 504 (CGC) with histidine (CAC). Although the patient was from a first‐cousin marriage, she was heterozygous for this mutation. The abnormality in the other allele, which is carried by the father, was not identified, except that it is neither of the two mutations responsible for the infantile Jewish Tay‐Sachs disease. Biosynthetic and immunoprecipitation studies in cultured fibroblasts showed synthesis of the α‐chain precursor, but the mature form of the α‐subunit was not detected.

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