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Molecular analysis of five Brazilian families, including eight patients presenting with nonclassic Tay-Sachs disease, was performed to identify frequent causative mutations and their correlation with clinical course. Three patients were affected by the B1 subacute variant and were shown to carry the R178H mutation (the DN allele), which is also common among Portuguese patients. Two of them were compound heterozygotes, whereas the third presented with the mutation in both alleles. Since Brazil was a Portuguese colony for over two centuries, common ancestry might be the probable explanation. The fourth patient presented with a juvenile phenotype and carries the R499H mutation, which has been reported only once worldwide and is associated with residual enzyme activity, responsible for a slower clinical course. The fifth family, of an Ashkenazi Jewish background, showed an extensive intrafamilial clinical variability among three affected sibs presenting with muscle atrophy, ataxia, and psychiatric symptoms. They were first diagnosed as having atypical spinal muscular atrophy and, subsequently, spinocerebellar ataxia, but, recently, the diagnosis of late-onset Tay-Sachs disease was confirmed based on reduced plasma hexosaminidase A activity and the G269S/InsTATC1278 genotype. It is therefore highly recommended to test patients with a similar clinical history for Tay-Sachs disease. In the same family, one first cousin committed suicide at the age of 24 years, presenting with a clinical phenotype that suggested an undiagnosed case and highlighting the effect of the intrafamilial clinical variability in delaying a prompt diagnosis. It is now recognized that his parents are, in fact, a carrier couple. Additionally, another relative had been previously identified as a heterozygote in a Tay-Sachs disease screening program, but the information was not shared among the family. Since this information might anticipate diagnosis and genetic counseling, it is advisable that heterozygote screening programs encourage families to share genetic information.

The authors report their experience in populational screenings, first regarding hyperphenylalaninemias at the city of S Paulo, by own programmation. In the same aminoacidopathies detection program, a similar methodology is being used in urine, in the children's health services of the State of S. Paulo. The same urine procedure is being used to select IEM of carbohydrates and mucopolysaccharides A programme similar to the one used for hyperphenylalaninemia is being performed for the detection of congenital hypothyroidism; T4 tests were made by radioimmunoassay (RIA) microtechnique in newborns and children in the first months of life. A similar experience in the detection of heterozygotes for GM2-ganglyosidosis type I (Tay-Sach disease) by performing the hexosaminidase A test is also reported. The importance of the performing of such populational screening tests, even in underdeveloped countries is stressed. Taking into account the high cost of the maintenance of patients with mental retardation (MR0, the cost of such programmes may become a saving whenever early diagnosis and therapy can avoid the MR.