Biochemical phenotyping of a single sibship with both cystinosis and Fabry disease

Two lysosomal storage diseases, cystinosis and Fabry disease, were diagnosed clinically in different members of a single sibship. The possibility that the affected sister and brother might have related disorders with disparate manifestations was pursued. The four principal family members were tested for heterozygote status with respect to serum and leukocyte alpha-galactosidase A activity, urinary trihexosylceramide excretion, and the capacity to engage in cystine counter-transport across leukocyte lysosome membranes. Results were consistent with classical autosomal recessive inheritance in the case of cystinosis and X-linked inheritance for Fabry disease, confirming that this family represents an example of two rare disorders occurring in the same sibship.