Chromosome 22 Ring
What is Chromosome 22 Ring?
Chromosome 22 Ring is an extremely rare condition caused by having an abnormal chromosome 22 that forms a ring. In this chromosome abnormality, a segment on the short (p) arm and a segment on the long (q) arm of 22 are missing, however, the amount of material lost varies from person to person. The remaining ends of chromosome 22 join together to make a ring shape. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as “p” and a long arm identified by the letter “q”. Chromosome 22 is an acrocentric chromosome, meaning that the centromere is near one end, creating a very small short (p) arm that does not contain genes that are relevant to development; thus, only the lost genes on the long (q) arm matter. The disorder is typically associated with moderate to severe mental retardation. Only approximately 100 cases have been reported of Chromosome 22 Ring.What causes Chromosome 22 Ring?
Chromosome 22 Ring results from loss (deletion) of genetic material from both ends of the 22nd chromosome and the joining of these ends to form a ring. Chromosome 22 Ring is usually caused by spontaneous or “de novo” errors very early in the development of the embryo. In such cases, the parents of an affected child typically have normal chromosomes, and the probability of having another child with the chromosomal abnormality is low. However, there have been reported cases in which Chromosome 22 Ring was inherited from a parent (familial transmission). In some familial cases, only a certain percentage of the parent’s cells may contain Chromosome 22 Ring, whereas other cells may have a normal chromosomal makeup (a finding known as “chromosomal mosaicism”).What are the symptoms of Chromosome 22 Ring?
Signs and symptoms of this disorder depend largely on where the breakpoint occurs on chromosome 22 and how much genetic material has been lost on the long (p) arm. While there is no consistent clinical picture, frequent findings of Chromosome 22 Ring include:- Developmental delay
- Moderate to severe learning difficulties or intellectual disabilities
- Small head
- Absent or delayed speech
- Hypotonia
- Unsteady manner of walking
- Hyperactivity
- Autistic behaviors
- Seizures
- Growth delay
How is Chromosome 22 Ring diagnosed?
In some cases, a diagnosis of Chromosome 22 Ring may be suggested before birth (prenatally) by specialized tests such as:- Ultrasound to reveal characteristic findings that suggest a chromosomal disorder or other developmental abnormalities in the fetus
- Amniocentesis, in which a sample of fluid that surrounds the developing fetus is removed and analyzed
- Chorionic villus sampling (CVS), which involves the removal of tissue samples from a portion of the placenta
