147 NEW VARIANTS OF PHOSPHORYLASE KINASE DEFICIENCY

Abstract

Three variants of phosphorylase kinase (PK) deficiency have been described, differing from one another by their genetic mode of inheritance and their organ involvement. The present report describes two additional variants for GSD IX: The first, in which the PK deficiency was reduced in muscle only (activity was 0.3 as compared to 2.6±1.5 U phosphorylase a/mg prot/min), with no indication of liver, erythrocyte or leukocyte involvement. The second variant presented in a 2-year-old boy with hepatomegaly and a slight tendency to fasting hypoglycemia. Blood cell PK activities were measured and are summarised in the table. The Km of leukocyte PK to phosphorylase b was normal. The difference in the patients' enzyme activity found in WBC as compared to RBC may be explained by the production of an unstable PK. The detection of additional variants of PK is not surprising in view of the fact that PK consists of 4 subunits which are coded on different chromosomes; thus various mutations are expected to be expressed in different tissues and to follow diverse modes of inheritance.