MUTATIONS IN THE LIVER-GLYCOGEN SYNTHASE GENE IN CHILDREN WITH HYPOGLYCEMIA DUE TO GLYCOGEN-STORAGE-DISEASE TYPE-0

Glycogen storage disease type 0 (GSD-0) is a rare form of fasting hypo glycemia presenting in infancy or early childhood and accompanied by h igh blood ketones and low alanine and lactate concentrations. Although feeding relieves symptoms, it often results in postprandial hyperglyc emia and hyperlactatemia. The glycogen synthase (GS) activity has been low or immeasurable in liver biopsies, whereas the liver glycogen con tent has been only moderately decreased, To investigate whether mutati ons in the liver GS gene (GYS2) on chromosome 12p12.2 were involved in GSD-0, we determined the exon-intron structure of the GYS2 gene and e xamined nine affected children from five families for linkage of GSD-0 to the GYS2 gene. Mutation screening of the 16 GYS2 exons was done by single-strand conformational polymorphism (SSCP) and direct sequencin g. Liver GS deficiency was diagnosed from liver biopsies (GS activity and glycogen content). GS activity in the liver of the affected childr en was extremely low or nil, resulting in subnormal glycogen content. After suggestive linkage to the GYS2 gene had been established (LOD sc ore = 2.9; P < 0,01), mutation screening revealed several different mu tations in these families, including a premature stop codon in exon 5 (Arg246X), a 5'-donor splice site mutation in intron 6 (G(+1)T-->CT), and missense mutations Asn39Ser, Ala339Pro, His446Asp, Pro479Gln, Ser4 83Pro, and Met491Arg. Seven of the affected children carried mutations on both alleles, The mutations could not be found in 200 healthy pers ons. Expression of the mutated enzymes in COS7 cells indicated severel y impaired GS activity. In conclusion, the results demonstrate that GS D-0 is caused by different mutations in the GYS2 gene.