Cytogenetics of Down’s Syndrome (Mongolism) I. Data on a Consecutive Series of Patients Referred for Genetic Counselling and Diagnosis

Abstract

The chromosome findings in a series of 173 Down’s syndrome or presumptive Down’s syndrome index patients, and a further 3 5 pairs of parents of Down’s syndrome index cases, are given. One hundred and forty-four index cases had primary G₂₁ trisomy; six were interchange trisomics, six were mosaics, and one was a chromatin positive male with XXY sex chromosomes and primary G₂₁ trisomy. Sixteen index patients whose diagnosis could not be clinically confirmed, were found to have normal chromosomes. The 35 pairs of parents all had normal chromosomes. In seven families (three index patients with primary G₂₁ trisomy, two with normal chromosomes and two index patients not studied) minor morphological chromosome anomalies were observed. The relevance of this data to the causal association of Down’s syndrome and G₂₁ trisomy, the frequency of mosaicism, double trisomy and association with other chromosome anomalies, is discussed.

Down syndrome: Cytogenetical epidemiology

“…This is much higher than would be expected if the two events were independent. A similar high number of double aneuploidies was observed by HAMERTON et al (1965). It is most likely that a tendency to non-disjunction exists and that the lower number of double aneuploidies in some studies might reflect a higher infant mortality in these cases.…”

A sex chromatin survey of newborn children in two London hospitals.

“…Double trisomy, G21/XXY, occurs with a frequency of 1 in 11,614 male births, which is considerably higher than would be expected by the chance association of the two conditions (Hamerton, Giannelli, and Polani, 1965). The findings in trisomy-18 are similar (Taylor, 1967).…”

Gender Affects Clinical Suspicion of Down Syndrome

“…Generally, the clinical diagnosis is straightforward and well-known to all medical workers [Mikkelsen, 1988]. However, misdiagnosis (false positive diagnosis) of Down syndrome was reported in numerous publications [Ahmed et al, 2005;Baccichetti et al, 1990;Ballesta et al, 1977;Engel et al, 1970;Fried et al, 1980;Hamerton et al, 1965;Melve et al, 2008;Szollar et al, 1983], being particularly high in neonates [Devlin & Morrison, 2004;Hindley & Medakkar, 2002]. Factors which alter suspicion of trisomy 21 are known to be early delivery and prematurity [Mikkelsen, 1988].…”