Sir: Carbohydrate-deficient glycoprotein syndrome (CDGS) type I is an inherited metabolic disorder with multisystemic abnormalities including psychomotor retardation, hypotonia, ataxia, growth failure, liver dysfunction, cerebellar hypoplasia and other clinical features [2]. There is a partial deficiency of carbohydrates in many glycoproteins caused by a failure to add N-linked carbohydrate chains. In most patients with type I CDGS the basic defect is phosphomannomutase (PMM) deficiency [3], an enzyme involved in the conversion of mannose-6-phosphate to mannose-1-phosphate. No definitive treatment is currently available for this disorder. Previous studies on cultured fibroblasts of patients with type I CDGS have demonstrated that defective N-glycosylation is corrected by providing mannose in a dose of≥ 250 μM to the culture medium [7]. We therefore studied whether oral supplementation of mannose may improve the characteristic biochemical abnormalities in type I CDGS and PMM deficiency. The male patient of German origin showed the characteristic clinical and biochemical signs of type I CDGS [6]. Diagnosis was based on the particular isoelectrofocusing (IEF) pattern of serum sialotransferrins. PMM activity in fibroblasts was decreased to 4%[3], and two missense mutations in the PMM2 gene (Phe119Leu/Arg141His) were found [5]. At the start of the oral mannose trial the patient was 12 months old. Mannose was obtained from Merck (Darmstadt, Germany). The patient was given oral doses of 0.17 g (1.0 mmol) mannose/kg body weight every 3.5 h for a total study period of 6 months.

Serum mannose concentration was analysed by an enzymatic method [1] and by gas chromatography/mass spectrometry [4]. Qualitative abnormalities of five different serum glycoproteins (transferrin, o1-antitrypsin, antithrombin III, o1-acid glycoprotein, o2-HS-glycoprotein) were regularly studied by IEF followed by immunoprinting (M. SchroÈder, WP Bieger, Munich, Germany)