IDENTIFICATION OF A MUTATION IN LIVER-GLYCOGEN PHOSPHORYLASE IN GLYCOGEN-STORAGE-DISEASE TYPE-VI

Glycogen storage disease type VI (GSD6) defines a group of disorders t hat cause hepatomegaly and hypoglycemia with reduced liver phosphoryla se activity. The course of these disorders is generally mild, but defi nitive diagnosis requires invasive procedures. We analyzed a Mennonite kindred with an autosomal recessive form of GSD6 to determine the mol ecular defect and develop a non-invasive diagnostic test. Linkage anal ysis was performed using genetic markers flanking the liver glycogen p hosphorylase gene (PYGL), which was suspected to be the cause of the d isorder on biochemical grounds. Mennonite GSD6 was linked to the PYGL locus with a multipoint LOD score of 4.7. The PYGL gene was analyzed f or mutations by sequencing genomic DNA. Sequencing of genomic DNA reve aled a splice site abnormality of the intron 13 splice donor. Confirma tion of the genomic mutation was performed by sequencing RT-PCR produc ts, which showed heterogeneous PYGL mRNA lacking all or part of exon 1 3 in affected persons. This study is the first to demonstrate that a m utation in the PYGL gene can cause GSD6. This mutation is estimated to be present on 3% of Mennonite chromosomes and the disease affects 0.1 % of that population. Determination of this mutation provides a basis for the development of a simple and non-invasive diagnostic test for t he disease and the carrier state in this population and confirms bioch emical data showing the importance of this gene in glucose homeostasis .