Detection of Equine X Chromosome Abnormalities in Equids Using a Horse X Whole Chromosome Paint Probe (WCPP)

摘要

Forty years ago, Tijo and Levan (1956) made the historic observation that the karyotype of Homo sapiens contained 46 chromosomes. Since then, chromosomal analysis has played an increasingly important role in the study of human and animal genetics. Changes in the number of individual chromosomes within a karyotype often lead to recognizable clinical abnormalities, as demonstrated, for example, by Lejeune (1959) when he reported that Down's syndrome in man is associated with an additional copy of chromosome 21. Today many other syndromes are well defined and are screened for regularly in cytogenetic laboratories (deGrouchy & Turleau, 1984) amongst which are a number of sex chromosome anomalies such as Turner's syhdrome (45.XO) and Klinefelter's syndrome (47, XXV). In man, the overall incidence of chromosomal abnormalities in newrborns is in the order of 1 in 200 (Thompson & Thompson, 1986). In contrast, chromosome analysis is ifot widely used in veterinary medicine. Early reports of chromosomal abnormalities with important consequences include the identification of a centric fusion associated with reduced fertility in dairy cattle (Gustavsson, 1969) and numerical abnormalities of the sex chromosomes associated with infertility in mares (Chandley elal, 1975). The karotype ofthe domestic horse consists of 64 chromosomes, with 13 autosomal pairs being metaceritric to sub-metacentric while 18 are acrocentric. The X is a large submetacentric chromosome and the Y a small acrocentric chromosome, Banding studies have been used togenerate a standardized numbering system for equine chromosomes (Richer et al, 1990) although this standard has now been updated (ISCNH, 1997), Few autosomal abnormalities have been identified in the horse, although trisomies of chromosomes 23, 26, 28, 30 and 31 have been observed (Bowling & Millon, 1990; Klunder el al., 1989; Power, 1987,1991; T, L, Lear, personal communication). Over 90% of the reported cases of chromosome anomalies involve the sex chromosomes and of these the XO syndrome accounts forapproximately 36% (Power, 1990), Mares with an XQ karyotype usually present -with infertility and in most cases they are small, have qver-angulated hind legs and show ovarian hypoplasia combined with clitoral byper-plasia. Other commonly, reported sex chromosome abnormalities in the horse include 64, XY sex reversal (Bowling et al., 1987), 63, XO/64, XX mosaicism (iong, 1989) and 65, XXX (Bowling el al., 1987).