Attempted detection of heterozygotes for maple-syrup-urine disease

Heterozygote detection in angiokeratoma corporis diffusum (Anderson-Fabry disease). Studies on plasma, leucocytes, and hair follicles

Heterozygote detection for angiokeratoma corporis diffusum (Anderson-Fabry disease, ACD), an X-linked disorder of glycosphingolipid metabolism was examined using alpha-galactosidase activity, an alpha-galactosidase/beta-galactosidase activity ratios (alpha/beta ratio) in leucocytes, plasma, and hair follicles; For leucocytes, 22 obligate heterozygotes, 25 suspected heterozygotes, and 47 control subjects were studied, while for plasma, the groups were 17 obligate heterozygotes and 35 controls. The alpha/beta ratio in plasma and leucocytes was clearly a better discriminator between obligate heterozygotes and controls than alpha-galactosidase activity alone, but still failed to detect 3 obligates with leucocytes and 2 with plasma. Discrimination was not improved by joint use of plasma and leucocyte alpha/beta ratios, but was improved by measurement of hair-follicle alpha/beta ratios. The interdecile range of log (alpha-galactosidase/beta-galactosidase activity) in 20 hair follicles from each of 4 obligate and 7 suspected heterozygotes was clearly different from 11 control subjects. Accordingly, for rapid screening for carriers of ACD, we recommend use of leucocyte or plasma alpha/beta ratios which should detect greater than 85% of heterozygotes. When results are equivocal, and ancillary information suggests heterozygous status, the more time-consuming measurement of hair-follicle alpha/beta ratios is a useful additional test.

Inborn errors of metabolism in the Maritimes, with special reference to maple-syrup-urine disease and Fabry's disease

1. The study of inborn errors of metabolism in man is of wide, general relevance to human biology and medicine, because these derangements are unique human models for the study of the sequence of normal metabolic events and their dependence upon genetic control. These disorders constitute naturally occurring mutations in man; as such, they afford the same opportunity for major contributions to human biology that bacterial mutants provide for molecular biology. 2. In terms of human suffering and cost, to affected kindred and the community at large, the importance of inborn errors of metabolism is out of all proportion to their small numerical incidence. Therefore, efforts must be intensified to identify affected individuals and carriers and to formulate methods of prevention and treatment. 3. The overall study of inborn errors of metabolism is illustrated by experience with two such disorders in the Maritime provinces.

Prenatal diagnosis and family studies in a case of propionicacidaemia

In a family with a history of two neonatal deaths, propionicacidaemia was diagnosed retrospectively from stored plasma as the cause of the second death during the mother's next pregnancy. Amniocentesis was performed and a culture of amniotic cells was assayed for propionyl CoA carboxylase activity. The absence of any detectable propionyl CoA carboxylase activity allowed the prenatal diagnosis of propionicacidaemia to be made. Treatment with biotin and a modified aminoacid diet was started in the immediate postnatal period. Investigation of propionyl CoA carboxylase in leucocytes from the parents, siblings and other relations of the patient failed to demonstrate intermediate enzyme activities in even the parents, who were presumably heterozygotes for this condition.