Chromosome 18 represents approximately 2.5% of the total DNA in cells and contains 200 to 300 genes that code for proteins essential for a variety of functions in the body. Partial deletions of the p and q arms can result in ring formation. Ring chromosome 18 is one of the rare structural chromosome abnormalities. This aberration can cause varied phenotypic manifestations ultimately leading to a suboptimal loss of body function. Structural abnormalities affect genes of the defunct part of the chromosome. Subsequent loss of protein translation leads to various genetic abnormalities, depending on the location and extent of the genes deleted during formation of the ring. Hence, there are various manifestations of this disorder. Most of the children with ring chromosomes show a failure to thrive beyond the extent expected from their chromosomal imbalances. The phenotypic diversity observed in Ring 18 is described. Chromosome abnormalities including ring 18 detected in our laboratory in a child with metabolic leukodystrophy are illustrated. The availability of preimplantation genetic diagnosis (PGD) in India and its benefits are highlighted.

Keywords: Ring Chromosome 18; Telomeres; Leukodystrophy; Microarray; NGS; FISH; PGD.