Hearing loss has been reported and may be related to ear canal atresia or stenosis. Umbilical and inguinal hernias have been reported in a small number of people with ring 18. Unilateral renal hypoplasia and aplasia have both been reported in individuals with ring 18. Hydronephrosis as well as pyelonephritis have also been reported in a few individuals. Cryptorchidism, hypospadias, and micropenis have been seen in males with ring 18, while females have been reported with hypoplastic labia. Foot abnormalities are common within the ring 18 population. Scoliosis as well as pectus excavatum have also been frequently reported. Several people with ring 18 have growth hormone deficiency. Hypothyroidism has also been reported in a minority of people. Cognitive ability varies; according to a literature review, the degree of impairment may fall anywhere between the mild and severe ends of the spectrum. Facial features of ring 18 include low-set, dysplastic ears, epicanthic folds, and hypertelorism. Micrognathia has also been reported. Genetic
Individuals with ring 18 have one of their two copies of chromosome 18 that has formed the shape of a ring. The ring is formed when the caps on  both the long arm (q) and the short arm (p) of one copy of chromosome 18 are lost and the new ends re-join to form the ring. Because the ring involves deletions of both the long arm (18q-) and the short arm (18p-) of chromosome 18, individuals with ring 18 can have features of both 18p- as well as distal 18q-.
TCF4 – In 2007, deletions of or point mutations in this gene, which is located on 18q, were identified as the cause of Pitt-Hopkins disease. This is the first gene that has been definitively shown to directly cause a clinical phenotype when deleted. If a deletion includes the TCF4 gene (located at 52,889,562-52,946,887), features of Pitt-Hopkins may be present, including abnormal corpus callosum; short neck; small penis; accessory and wide-spaced nipples; broad or clubbed fingers; and sacral dimple. Those with deletions inclusive of TCF4 have a significantly more severe cognitive phenotype. TSHZ1 - Point mutations and deletions of this gene, located on 18q, are linked with congenital aural atresia  Individuals with deletions inclusive of this gene have a 78% chance of having aural atresia. Critical regions – Recent research has narrowed the critical regions for four features of the distal 18q- phenotype down to a small segment of distal 18q, although the precise genes responsible for those features remain to be identified. Haplolethal Regions - There are two regions on chromosome 18 that has never been found to be deleted. They are located between the centromere and 22,826,284 bp (18q11.2) and between 43,832,732 and 45,297,446 bp (18q21.1). It is hypothesized that there are genes in these regions that are lethal when deleted. Nomenclature
The phrase “ring 18” refers to the shape that the normally linear chromosome assumes when one tip of the chromosome joins the other. A ring-shaped chromosome is the result.