[Trisomy 18: phenotypic and biochemical variability].

We report a case of Edward's syndrome showing some symptoms infrequently described in trisomy 18. The authors suggest that the phenotypic expression of symptoms rarely observed in the syndrome may be better interpreted as non specific consequence of the chromosomal imbalance, rather than directly related to genes on chromosome 18. A gene dosage effect for the enzyme Peptidase A, whose gene is mapped on chromosome 18, was also observed.