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Glucokinase is one of the most important regulators of fasting glucose levels. There are several mutations in the glucokinase gene (GCK) which are linked with monogenic diabetes. Recently, a polymorphism in its promoter has been described, which is associated with impaired fasting glucose levels. We present a 7 years and 7 months old boy with overweight and a familial background of diabetes in two previous generations. In the oral glucose tolerance test, he had impaired fasting glucose levels and after two hours, with a high insulin response. Laboratory abnormalities improved after weight loss, but he maintains a slight fasting hyperglycaemia. The molecular study of the most common monogenic diabetes forms, MODY subtypes 1, 2, and 3, was negative. The allelic variant G/A was however detected at the GCK promoter polymorphism rs1799884., (Copyright © 2011 Asociación Española de Pediatría. Published by Elsevier Espana. All rights reserved.)

Three groups of disorders are reviewed: the syndromes with carbohydrate deficient glycoproteins, congenital errors of metabolism involving purines and pyrimidines, and finally those of the neurotransmitters. Individually these disorders are rare, but as a group include many different pathological conditions. We list the clinical symptoms and laboratory data in patients with different enzyme deficiencies. Although some disorders have specific clinical characteristics, most have nonspecific clinical features which makes diagnosis difficult.