Elucidation of an unbalanced chromosome translocation by gene dosage studies

A chromosome abnormality, 46,XY,1p+, was detected in cultured amniotic fluid cells. The chromosomes of both parents were normal and it was impossible to recognise the extra chromosomal material using current banding techniques. The activity of acid alpha-glucosidase was found to be consistently higher than controls whereas activity of several other lysosomal enzymes, galactokinase and thymidine kinase was not. The results suggest that the extra material is that part of the long arm of chromosome 17 bearing the gene for acid alpha-glucosidase but not the genes for galactokinase and thymidine kinase. This would narrow the assignment of the acid alpha-glucosidase locus to 17q22 leads to 17 qter.