PHOSPHOSERINE PHOSPHATASE DEFICIENCY IN A PATIENT WITH WILLIAMS-SYNDROME

Decreased serine levels were found in plasma and cerebrospinal fluid ( CSF) of a boy with pre- and postnatal growth retardation, moderate psy chomotor retardation, and facial dysmorphism suggestive of Williams sy ndrome. Fluorescence in situ hybridisation with an elastin gene probe indicated the presence of a submicroscopic 7q11.23 deletion, confirmin g this diagnosis. Further investigation showed that the phosphoserine phosphatase (EC 3.1.3.3.) activity in lymphoblasts and fibroblasts amo unted to about 25% of normal values. Oral serine normalised the plasma and CSF levels of this amino acid and seemed to have some clinical ef fect. These data suggest that the elastin gene and the phosphoserine p hosphatase gene might be closely linked. This seems to be the first re port of phosphoserine phosphatase deficiency.