Substitution of alanine543 with a threonine residue at the carboxy terminal end of the beta-chain is associated with thermolabile hexosaminidase B in a Jewish family of Oriental ancestry.

Thermolabile forms of the lysosomal enzyme beta-hexosaminidase B (Hex B), likely to result from different genetic defects, have been described. Ten individuals in five generations of a family of Oriental Jewish ancestry were identified biochemically as carriers of a thermolabile Hex B form. The beta-chain thermolability was found to be associated with the presence of a G --> A transition at nucleotide 1627 of the HEX B gene causing the substitution of Ala543 with a threonine. Oriental Jew whose Hex B was heat labile. Since thermolabile Hex B has been shown to occur more frequently among Jews of Oriental origin, the Ala543 --> Thr mutation may be the common mutation associated with beta-chain thermolability in this ethnic group.