Fetal Loss: A Genetic Insight of the De Novo Accessory Bi-Satellited Marker of Chromosome 22P

Abstract

Supernumerary Marker Chromosomes (SMC) follow non mendelian fashion in their inheritance, and are reported in variety of phenotypes. Although markers that contain satellites/bi-satellite variations of short arms do not confer any phenotypic alterations, it affects the fertility, vigour and interferes at non-disjunction during cell division and proves lethal to foetus. We report a couple wherein wife had Recurrent Early Pregnancy Loss (REPL) due to loss of fetal cardiac activity and husband with oligoasthenospermia. The cytogenetic analysis of the wife showed 46,XX,9qh+ karyotype and that of husband revealed 47,XY,+mar karyotype. Delineation of marker was initiated using NOR (Nucleolar Organizer Region), C-banding conventional techniques in combination with Fluorescence In Situ Hybridization (FISH) using Whole Chromosome (WCP) and Locus Specific Identifier (LSI) probes. Marker was characterized to be of chromosome 22 origin with satellites on either side of the centromere inferring it to be a bi-satellited iso-chromosome 22p with its occurrence as partial tetrasomy. Our study attempts to provide a comprehensive understanding of this cytogenetic rearrangement and its possible consequences in fertility and REPL. Author SummaryFor the successful pregnancy outcome(s), many etiological factors like uterine anomalies, endocrinological factors, chromosomal anomalies etc., play a significant role emphasizing their importance resulting in the healthy offspring/progeny. Any disturbance or ambiguity in these factors results in fetal loss. Among these, chromosomal abnormalities of the genitors and their subsequent transmission contribute to a major extent in affecting the full term pregnancy outcome causing reproductive failure. Here we present a case where in accessory bi-satellited small supernumerary marker of chromosome 22p origin in the oligoasthenospermic (infertile) male partner, results in lethality of fetus due to the errors in meiotic segregation. We discuss its mechanism of iso-chromosome formation and occurrence of partial tetrasomy of chromosome 22p due to four fold dosage of centromeric sequences where in the rest of the chromosomal region of 22q is deleted including Di-George, leading to the absence of cardiac activity in fetus and subsequently miscarriage(s) in the first trimester in the female partner.