Distribution and characterization of a Sandhoff disease-associated 50-kb deletion in the gene encoding the human β-hexosaminidase β-chain

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Abstract
A 50-kb deletion was demonstrated in the gene encoding for the β-subunit of human hexosaminidase (HEXB), using field inversion gel electrophoresis (FIGE) of SfiI-digested chromosomal DNA from patients with Sandhoff disease. We investigated 14 patients from different parts of Europe and found no deletion in 5 patients, 2 patients homozygous for the deletion, and 7 patients with the deletion in one allele. The distribution of the 50-kb deletion was approximately in agreement with the Hardy-Weinberg equilibrium. The deletion was characterized using chromosomal DNA from one of the two homozygous patients. Restriction fragments were hybridized with a 1.6-kb (almost complete) and a 0.4-kb (5′) HEXB cDNA clone. It appeared that the deletion started in intron 5, extending in the 5′ direction and causing the loss of exon 1–5 and the promoter area of the HEXB gene.