Abstract:
The problem. Eighty-seven patients clinically diagnosed as having Down's syndrome were studied by chromosome analysis at Woodward State Hospital, Woodward, Iowa, during June and July of 1972.
Procedure. A cytogenetic analysis was made on chromosomes prepared from leucocytes cultured from peripheral blood. Ten cells were counted and karyotypes prepared for each patient.
Findings. Among the eighty-seven patients, 54 males and 33 females, 60 (69%) were trisomic, 26 (29.9%) showed possible mosaicism and 1 (1.15%) carried a translocation. Three of the residents, including the patient with a translocation, were one of a set of twins.
Conclusion. The frequency of Down's syndrome based on a Woodward population of 750 residents was 11.6%. This frequency is in agreement with a reported frequency of 11.2% individuals with Down's syndrome determined from a 1967 census of 23,211 people in institutions for the mentally retarded. The frequency of 60 trisomic Down syndrome patients (69%) was lower than the 93% figure found by most investigators. The observed frequency (1.15%) of translocation Down's syndrome is lower than reported frequencies of 3 to 4% for other institutions. A frequency of mosaic Down's syndrome in the Woodward population of 29.9% is considerably higher than the 1 to 2% reported elsewhere for similar populations. The observed cases of presumptive mosaicism may include cases of regular trisomy which wiil be resolved by more extensive cytogenetic analysis.
Recommendations. A follow-up study to more completely characterize the mosaic Down's syndrome population is warranted to resolve the large observed deviation.
