Thermolabile Hexosaminidase (Hex) B: Diverse Frequencies among Jewish Communities and Implication for Screening of Sera for Hex A Deficiencies

Twenty unrelated people with thermolabile beta-hexosaminidase (Hex) B were identified in random samples of 41,561 adult Israeli Jews whose sera were screened for Hex A levels. Eighteen of them originated from contiguous Middle Eastern countries (n = 1,337) and only 2 were Ashkenazi Jews (n = 38,388). None was found among the screened Moroccan Jews (n = 1,524). The commonly used screening test for detection of Tay-Sachs disease (TSD) carriers is the serum Hex heat inactivation method (HIM), which is based on the assumption that Hex A is the only thermolabile component of Hex; However, in the presence of thermolabile Hex B, HIM could lead to false-negative results. Since TSD is very rare among Mideastern Jews while thermolabile Hex B is very rare among Ashkenazi and Moroccan Jews, it is concluded that at present there is almost no risk of such false-negative results. In order to further reduce this risk it is recommended that screening of people of Mideastern or mixed ancestry be done with HIM in leukocytes rather than in serum or with the specific substrate for Hex A in serum.