[Genetic advances in galactosialidosis].

Galactosialidosis is an autosomal recessive inherited metabolic disorder induced by the deficiency of beta-galactosidase and neuraminidase. It can be classified into the early infantile form, the late infantile form, and the juvenile/adult form, by clinical characteristics. This disease has been known to be caused by the lack of protective protein. The human protective protein is synthesized as a 54 kD precursor and then processed to the mature form, a heterodimer of 32 and 20 kD polypeptides. The mature protective protein forms a complex with beta-galactosidase and neuraminidase, stabilizing beta-galactosidase and activating neuraminidase. Recently, this protective protein was found to have other multiple functions including activities of carboxypeptidase, esterase and deamidase. The nature of abnormality of the protective protein in the three subtypes of galactosialidosis however has not yet been well elucidated. On the other hand, a cDNA of the protective protein was cloned, and point mutations in the protective protein gene were found in a Japanese family with the adult form, and in Canadian and Italian patients with the late infantile form. We also detected the same point mutation in two Japanese patients with the adult form. Discovery of the genetic defect in different subtypes of galactosialidosis will contribute to the study on the nature of abnormality in the protective protein itself.