MOLECULAR AND BIOCHEMICAL-ANALYSIS OF PROTECTIVE PROTEIN CATHEPSIN-A MUTATIONS - CORRELATION WITH CLINICAL SEVERITY IN GALACTOSIALIDOSIS/

Mutations in the gene encoding lysosomal protective protein/cathepsin A (PPCA) are the cause of the lysosomal disorder galactosialidosis (GS ). Depending on age of onset and severity of the symptoms, patients pr esent with either an early infantile (El), a late infantile (LI), or a juvenile/adult (J/A) form of the disease. To study genotype-phenotype correlation in this disorder, we have analyzed the mutations in the P PCA gene of eight clinically different patients, In two El and one J/A patient, we have identified four novel point mutations (Val104Met, Le u208Pro, Gly411Ser and Ser23Tyr), that prevent phosphorylation and, he nce, lysosomal localization and maturation of the mutant precursors, T wo amino acid substitutions (Phe412Val and Tyr221Asn) are shared by fi ve LI patients, These mutations appear to be pathognomonic for this ph enotype, and determine the clinical outcome depending on whether they are present together or in combination with other mutations, The latte r include a single base deletion and a novel amino acid change (Met378 Thr), which generates an additional glycosylation site. Within the LI group, patients carrying the Phe412Val mutation are clinically more se vere than those with the Tyr221Asn substitution, This is in agreement with the biochemical behavior of the Asn221-mutant protein, that is, l ike the Phe412Val protein, phosphorylated, routed to lysosomes and pro teolytically processed, but its intralysosomal stability is intermedia te between that of wild-type PPCA and Val412-PPCA. Overall, these resu lts may explain the clinical heterogeneity observed in GS patients and may help to correlate mutant allelic combinations with specific clini cal phenotypes.