To the Editor.—We have not experienced any clinical difficulty in distinguishing the Smith-Lemli-Opitz (S-LO) syndrome phenotype from that of the 4p—syndrome. The craniofacies are usually different. For example in the 4p—syndrome they tend towards hypertelorism and short philtrum whereas in the S-L-O syndrome the tendency is toward ptosis, anteverted nostrils, and relative scaphycephaly. Other differences are emphasized by Mace and Cunningham.
The Smith-Lemli-Opitz syndrome is the more difficult diagnosis to be secure about since there is no laboratory test to "confirm" the clinical diagnosis. We would agree with Mace and Cunningham, that a chromosome study should be considered in any patient for whom there is insecurity about a clinical diagnosis of the S-L-O syndrome. However, we have not as yet evaluated a patient for whom our initial differential diagnosis included both of these disorders.