A diagnostic survey of patients referred for chromosome analysis.

Out of 692 patients referred for chromosome analysis because of abnormal clinical features, 199 (28.7%) had chromosomal abnormalities. In addition, assessment of the abnormal phenotypic features and the data of other (laboratory, X-ray, etc.) examinations revealed 25 (3.6%) single gene disorders, 25 (3.6%) recognizable syndromes or associations of unknown aetiology, and in 4 cases (0.6%) environmental agents were established as possible aetiological factors. Altogether, of the 692 cases, 253 (36.5%) had a definitive diagnosis, while the remainder 439 were undiagnosed. These results suggest that (i) chromosome analysis is worthwhile if the patient has significant clinical abnormalities, and (ii) a request for chromosome analysis should be viewed as one step in syndrome identification, so that a normal karyotype should stimulate the physician to further efforts to establish a diagnosis.