C syndrome, also known as Opitz trigonocephaly syndrome, is a rare disorder transmitted as a result of "gonadal mosaicism". Mosaicism refers to a condition in which a person has cells that differ from each other in genetic makeup. The difference is usually a variation in the number of chromosomes. Normally, all body cells would have 46 chromosomes, but in mosaicism, some cells may have 45 or 47. Mosaicism occurs as a result of an error in cell division very early in fetal development.
Affected individuals are born with a malformation in which the head is a triangular shape due to premature union of the skull bones (trigonocephaly), a narrow pointed forehead, a flat broad nasal bridge with a short nose, vertical folds over the inner corners of the eyes, an abnormal palate that is deeply furrowed, abnormalities of the ear, crossed eyes (strabismus), joints that are bent or in a fixed position, and loose skin. Developmental and learning disabilities are common.
One of the distinguishing features of C syndrome is a condition in which the skull is a triangular shape primarily due to premature closure of the bones (trigonocephaly). Patients with this disorder also have a distinct face in which the nasal bridge is broad with a short nose, and there are vertical folds over the inner corners of the eyes (epicanthus). A deeply furrowed palate in the mouth, abnormalities of the outer ear, crossed eyes (strabismus), joints that may be bent in a fixed position or dislocated, and loose skin are all features typically found in patients with C syndrome.
Epicanthus, retardation, loss of muscle tone, abnormalities of the sternum, facial palsy, webbed fingers and/or toes, short limbs, heart defects, failure of one or both testicles to move down into the scrotum (cryptorchidism), abnormalities of the kidneys and lungs, deformity of the lower jaw and/or seizures may also be found in individuals with C syndrome.
Until recently C syndrome was thought to be transmitted as an autosomal recessive trait. However, it is now believed that the disorder occurs as a result of gonadal mosaicism. It is not known at the current time what chromosome the gene defect is on. Research is in progress to identify the gene.
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.
All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Only about 70 cases have been reported in the world’s medical literature. C syndrome is a very rare disorder that seems to affect males and females in equal numbers.
When Trigonocephaly is severe surgery may be performed to relieve the pressure on the brain and cosmetically improve facial appearance. Other treatment is symptomatic and supportive.
Genetic counseling may be of benefit for patients and their families.
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