Ring Chromosomes and Associated Disorders: A Review

Abstract

Ring chromosomes are formed due to rejoining or breaking in either one or both the chromosome arms. Any chromosome can form such structure and thus a specific ring chromosome will have an altogether distinct size and inherited content. Of intrigue are ring chromosomes 14 and X that have a remarkable relationship with epilepsy and seizure beginning in early years of life. Phenotypic characteristics associated with ring chromosomes are very much disparate and this may be due to any deletion caused by ring arrangement. Other reason may be the imbalances occurred due to ring instability. Extreme deficiency of development without major deformity is a very usual observation in the carrier of the ring chromosomes. Such phenotypic expressions are termed as "ring disorder" and they are strictly related with mitotic instability and ring behavior and does not dependent on the chromosome engaged. In case of ring chromosomes, it is not possible to exactly correlate genotype-phenotype because all the determining factors mostly variegate depending on the magnitude of deletion during ring development. Also, ring instability and the level of mosaicism add extra degree of pleomorphism. In spite of the fact that ring chromosomes generally emerge as de-novo events, filial transmission of rings from carrier to progeny is portrayed and pre-birth diagnosis for any pregnancies should be appraised.