Summitt syndrome is an extremely rare genetic disorder characterized by malformations of the head, abnormalities of the hands and/or feet, and obesity. The syndrome is inherited as an autosomal recessive genetic trait. Some researchers believe that Summitt syndrome is one of seven closely related forms of a disorder characterized by characteristic malformations of the head and webbing between several toes and/or fingers (acrocephalopolysyndactyly). The malformations of the head are the result of the premature closings of the seams (cranial sutures) between the bony plates that make up the skull. Of the various forms of this disorder, many geneticists believe that Summitt syndrome is closely related to Carpenter syndrome (acrocephalopolysyndactyly type II).
In Summitt syndrome, the fibrous joints between the bones in the skull (cranial sutures) close prematurely (craniosynostosis), causing the head to grow upward at an accelerated rate. As a result, the head appears long, narrow, and pointed at the top (tower skull). Affected individuals also have webbed or fused fingers and/or toes (syndactyly) and are usually extremely overweight (obese). Other features may include vertical folds of skin over the eyes’ inner corners (epicanthal folds), delayed tooth eruption, an abnormally narrow roof of the mouth (palate), a malformed hip joint (coxa valga), and/or knock knees, that is, knees that are abnormally close together and ankles that are abnormally wide apart (genu valgum). Males with Summitt syndrome may have an abnormal enlargement of one or both breasts (gynecomastia). Intelligence is typically within normal limits.
Summitt syndrome is inherited as an autosomal recessive trait. The precise location of the changed gene has not yet been determined.
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.
Summitt syndrome is an extremely rare disorder that is believed to affect males and females in equal numbers. There have been too few cases reported to determine whether the disorder is more prevalent among males or females. The number of affected individuals is thought to number only about 12, of whom at least two were the children of closely related parents.
Summitt syndrome can be detected at birth, based upon a clinical evaluation and characteristic physical findings. Surgical correction of malformations is the primary treatment. Early craniofacial surgery may be performed to correct the premature closure of the bones in the skull (craniosyn-ostosis). Additional craniofacial surgery may be done later in life as well as surgery to correct deformities of the hands and/or feet.
Other treatment is symptomatic and supportive. Genetic counseling will be of benefit for people with Summitt syndrome and their families.
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