Phosphoserine phosphatase deficiency ina patient withWilliams syndrome

Decreasedserinelevels werefoundin plasmaandcerebrospinal fluid (CSF)ofa boywithpre-andpostnatal growthretardation, moderatepsychomotor retardation, andfacial dysmorphismsuggestive ofWilliams syndrome.Fluorescence in situhybridisation withan elastin gene probeindicated thepresence ofasubmicroscopic 7qI1.23deletion, confirming thisdiagnosis. Furtherinvestigation showedthatthephosphoserine phosphatase (EC3.1.3.3.) activity inlymphoblasts andfibroblasts amountedtoabout 25% ofnormalvalues. Oralserinenormalised theplasmaandCSFlevels ofthis aminoacidandseemedtohavesomeclinicaleffect. Thesedatasuggest thatthe elastingene and the phosphoserine phosphatase genemightbeclosely linked. Thisseemsto be thefirst reportof phosphoserine phosphatase deficiency. (JMed Genet 1997;34:594-596)