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During the last 5 years 2057 children under the age of 5 with various neurologic symptoms with the suspected diagnosis of lysosomal storage diseases were referred to our hospital from different universities and state hospitals. We were able to separate sphingolipidoses by lysosomal enzyme screening. A total of 300 patients (15%) with sphingolipidoses were diagnosed; there were deficiencies of arylsulfatase A [metachromatic leukodystrophy (MLD)] in 93 (31%), hexosaminidase [Sandhoff disease (SHD)] in 62 (20.7%), hexosaminidase A [Tay-Sachs disease (TSD)] in 15 (5%), beta-galactosidase (GM1 gangliosidosis) in 35 (11.7%), alpha-galactosidase (Fabry disease) in one (0.3%) cerebroside beta-galactosidase (Krabbe disease) in 65 (21.7%) and glucosylceramidase (Gaucher disease) in 29 (9.6%). SHD (20.7%), MLD (31%) and Krabbe disease (21.7%) were common. Prenatal enzymatic diagnosis was made in 70 at risk pregnancies, 64 for TSD and SHD, three for MLD and three for GM1 gangliosidosis by using chorionic villus biopsy in 54, cord blood samples in 12 and cultured amniotic fluid cells in four. Seventeen fetuses were found to be affected. We have calculated the relative frequency and minimum incidence of sphingolipidoses in Turkey. The combined incidence of sphingolipidoses is 4.615 per 100,000 live births. The calculated incidences are 1.43, 0.95, 1, 0.23, 0.54, 0.45, 0.015 per 100,000 live births for MLD, SHD, Krabbe, Gaucher, TSD, GM1 gangliosidosis and Fabry diseases, respectively. The real incidence, which covers all subtypes of this group of diseases, should be greater than this number. The results suggested that, as a group, sphingolipidoses are relatively common and represent an important health problem in Turkey and some rare autosomal recessive diseases of Turkey are due to 'founder effect' created by consanguineous marriages.

Pseudodeficiency (Pd) in arylsulfatase A (ASA) is a relatively frequent condition in healthy individuals. It produces a reduction in enzyme activity similar to that found in metachromatic leukodystrophy (MLD). A variable incidence of the Pd allele was found in different populations; it was 10-20 times higher than that of metachromatic leukodystrophy. Twelve of the 52 unrelated, healthy individuals were found to be heterozygous for the ASA Pd allele. In Turkey we estimated the incidence of the Pd allele as 11.5 percent. Out of 18 cases with MLD, one patient was found homozygous for the Pd allele and the other patient was found heterozygous.