MOLECULAR CYTOGENETIC CHARACTERIZATION OF AN inv(Y)(p11.2q11.221~q11.222) IN A SYRIAN FAMILY
Al-Achkar W1,*, Wafa A1, Al-Ablog A1, Moassass F1, Liehr T2
*Corresponding Author: Professor Walid Al-Aachkar, Department of Molecular Biology and Biotechnology, Division of Human Genetics, Atomic Energy Commission of Syria, P.O. Box 6091, Damascus, Syria; Tel.: +963- 11-213-2580; Fax: +963-11-611-2289; E-mail: ascientific@aec.org.sy
page: 73

DISCUSSION

Constitutional chromosomal abnormalities are an important cause of miscarriage, infertility, congenital anomalies, and mental retardation in humans. The frequency of structural chromosomal abnormalities has been estimated as 0.25% in live-born infants [13]. Chromosomal polymorphisms of the constitutive heterochromatin regions of chromosomes 1, 9, 16, and the Y-chromosome have been reported [14]. Mental retardation results from a defect in the structure and function of the neuronal synapse. Its worldwide incidence [intelligence quotient (IQ <70)] is ~2.0-3.0%. Males are found to be more affected than females. The risk of mental retardation is higher in children with congenital structural defects [15]. The cause of mental retardation may be genetic (30.0%) or environmental, congenital or acquired. Chromosomal aberrations account for 15.0% of mentally retarded individuals. Several types of structural aberrations are also known to cause mental retardation, the common ones being deletions, duplications, inversions, translocations and/or isochromosome formation [15]. Isodicentric Y chromosomes [idic(Y)] are formed by homologous crossovers between opposing arms of palindromes on sister chromatids. The authors propose that intrapalindrome sequence identity is maintained via non crossover pathways of homologous recombination. DNA double-strand breaks that initiate these pathways can be alternatively resolved by crossovers between sister chromatids to form idic(Y) chromosomes, with clinical consequences ranging from spermatogenic failure to sex reversal and Turner syndrome [6]. In all inv(Y) chromosomes cases previously described, which appear metacentric after banding analysis, the inversion breakpoints on the short arm in Yp11.2 fall in a gene-poor region of X-transposed sequences proximal to the pseudo autosomal regions (PAR1) on the X- and Y-chromosomes at the end of the short (p) arm SRY [16,17]. However, in our familial cases, the long arm inversion breakpoint maps proximal to the fertility genes CDY and DAZ in Yq11.223, resulting in our familial inv(Y)-type II. A similar familial inv(Y) case has been published [17]. In conclusion, we present a detailed molecularcyto- genetic characterization of a family who had an inv(Y)p11. 2q11.221~q11.222 with mental retardation features but an otherwise normal phenotype. However, molecular analysis of some genes implicated in mental retardation and detection of small gains or losses of genetic material using appropriate new high-resolution test methods and/or genome sequencing should be considered for future studies.



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