HUMAN FRUCTOSE-1,6-BISPHOSPHATASE GENE (FBP1) - EXON-INTRON ORGANIZATION, LOCALIZATION TO CHROMOSOME BANDS 9Q22.2-Q22.3, AND MUTATION SCREENING IN SUBJECTS WITH FRUCTOSE-1,6-BISPHOSPHATASE DEFICIENCY

Fructose-1,6-bisphosphatase (EC 3.1.3.11) is a key regulatory enzyme o f gluconeogenesis that catalyzes the hydrolysis of fructose-1,6-bispho sphate to generate fructose-6-phosphate and inorganic phosphate. Defic iency of fructose-1,6-bisphosphatase is associated with fasting hypogl ycemia and metabolic acidosis because of impaired gluconeogenesis. We have cloned and characterized the human liver fructose-1,6-bisphosphat ase gene (FBP1). FBP1, localized to chromosome bands 9q22.2-q22.3 by f luorescence in situ hybridization, consists of seven exons that span > 31 kb, and the six introns are in the same position as in the rat gene . FBP1 was screened for mutations in two subjects with fructose-1,6-bi sphosphatase deficiency. Four nucleotide substitutions were identified , two of which were silent mutations in the codons for Ala-216 (GC (T) under bar --> GC (C) under bar and Gly-319 (GG (G) under bar --> GG ( A) under bar. The other substitutions were in intron 3, a C --> T subs titution 7 nucleotides downstream from the splice donor site, and in t he promoter region, an A --> T substitution 188 nucleotides upstream f rom the start of transcription. These nucleotide substitutions were al so found in normal unaffected subjects and thus are not the cause of f ructose-1,6-bisphosphatase deficiency in the two subjects studied. The molecular basis of hepatic fructose-1,6-bisphosphatase deficiency in these subjects remains undetermined but could result from unidentified mutations in the promoter that decrease expression or from mutations in another gene that indirectly lead to decreased fructose-1,6-bisphos phatase activity. (C) 1995 Academic Press, Inc.