Abstract: Objective：To report the first case of fructose-1,6-bisphosphatase (FBPase) deficiency diagnosed by genetic sequencing in China, and to improve the cognition of this rare disease. Methods:The clinical and laboratory characteristics of FBPase deficiency were reviewed, and the findings of direct sequencing of genomic DNA described, and published literature on FBPase deficiency reviewed. Results: A 23-month-old boy was repeatedly admitted for 5 times with recurrent onset of lethargy and drowsiness every time after diarrhea and vomiting for 2－3 days during the last 7 months after being weaned, and he had convulsion this time. On admission, his physical examination showed tachypnea, and mild hepatomegaly, and he had normal physical and mental development. His paternal-grandparents had cousinship, and his parents were collateral relatives in the fifth generation. The laboratory findings revealed severe hypoglycemia, lacticacidemia, metabolic acidosis, ketonemia and hyperuricacidemia. After intravenous infusion of glucose, bicarbonate and antibiotics, there was a dramatic clinical improvement in a short time. Urine organic acids analyses ever showed an elevation of gluconeogenetic substrates including lactic acid, ketone and glycerol. The molecular analysis of liver fructose-1, 6-bisphosphatase (FBP1) gene showed a homozygous mutation with one G residue insertion at base 961 in exon 7(c.960/961insG), resulting in a reading frame shift mutation of 320th amino acid and premature termination at 333th amino acid. This mutation had been reported to be the most common mutation among patients with FBPase deficiency. Frequent feeding by avoiding taking in too much sweet food, restriction of food with high protein and fat, and the use of uncooked starch had been taken after our patient was discharged from the hospital. There had been no attack in the last 9 months. Conclusion: Clinicians must consider the diagnosis of FBPase deficiency when confronted with the patient who has episodes of severe hypoglycemia and lacticacidemia, especially accompanied by metabolic acidosis and ketonemia, which are typically triggered by infection and fasting. Early diagnosis, urgent treatment of hypoglycemia and appropriate diet control can prevent death, improve growth and quality of life of these children.

Key words: Fructose-1,6-bisphosphatase deficiency, Genetic testing, Hypoglycemia, Acidosis, lactic