Dyschondrosteosis is a very rare inherited disorder characterized by unusually shortened, bowed bones in the forearms (radius and ulna), abnormal deviation of the wrist toward the thumb side of the hand due to shortening of the radius and dislocation of the end portion of the ulna (Madelung deformity), unusually short lower legs, and associated short stature (mesomelic dwarfism). Affected individuals may also exhibit abnormalities of the large bone of the upper arm (humerus); abnormal bony growths projecting outward from the surface of the shin bones (exostoses of the tibia); unusually short, broad bones in the fingers and toes; and/or abnormalities of the hipbone (i.e., coxa valga). Dyschondrosteosis appears to affect females more severely than males. The disorder is inherited as an autosomal dominant or "pseudoautosomal" trait.
Individuals with dyschondrosteosis have abnormally short legs and associated mild short stature (mesomelic dwarfism). The degree of short stature varies from case to case.
Affected individuals also have an abnormality of the wrist known as Madelung deformity. In Madelung deformity, malformation (i.e., bowing and shortening) of the bones in the forearms (radius and ulna) and dislocation of the ulna results in abnormal deviation of the wrist toward the thumb side of the hand. In many cases, individuals with the disorder may have a limited range of movements of the wrists and elbows and/or may exhibit progressive degeneration, stiffness, tenderness, and pain of certain joints (osteoarthritis).
Additional symptoms found in individuals with dyschondrosteosis may include deformities of the large bone of the upper arm (humerus); an abnormal growths on the surface of the large bone in the middle of the lower leg (exostoses of the tibia); short, thick middle bones of the hand (metacarpals), fingers, and toes (phalanges); the forearm may be bent or twisted outward (cubitus valgus); a defect of the hip in which the thigh bone angles out to the side of the body (coxa valga); and/or a form of arthritis in which one or more of the large joints have tissue changes causing degeneration (osteoarthritis).
Dyschondrosteosis is inherited as an autosomal or pseudoautosomal dominant trait.
Human traits, including the classic genetic diseases, are the product of the interaction of a pair of matched genes, one received from the father and one from the mother. In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed “dominating” the other normal gene and resulting in the appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.
Pseudoautosomal inheritance is an extremely rare occurrence that involves a gene from either the X or Y chromosome. Genes are found on chromosomes, which 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 that normally consists of an X and Y chromosome for males and two X chromosomes for females. Chromosomes 1 through 22 are known as autosomes; the X and Y chromosomes are known as sex chromosomes.
A gene on an autosome may be passed on to either a male or female child with equal likelihood. This is referred to as autosomal inheritance. However, the sex chromosomes (X and Y) are not passed on equally because a father transmits his X chromosome to his daughters and his Y chromosome to his sons. This is referred to as sex-linked inheritance.
A key aspect of sex-linked inheritance is the lack of matched gene pairs between X and Y chromosomes. However, very small areas of the X and Y chromosome have matched genes. During the normal division of reproductive (sex) cells (meiosis), these areas pair up and “cross over”. The genes located in these areas transmit in a fashion similar to genes found on autosomes (pseudoautosomal inheritance).
Investigators have determined that some cases of dyschondrosteosis may be caused by disruption or changes (mutations) of the short stature homeobox (SHOX) gene located on the short arm of the X or Y chromosome.
Dyschondrosteosis is a very rare disorder that can affect males or females. There have been more cases of dyschondrosteosis reported in females than in males by a 4:1 ratio, but some scientists believe that this is because females tend to have more severe symptoms.
The treatment of dyschondrosteosis is symptomatic and supportive. Some individuals with dyschondrosteosis may have severe Madelung deformity of the wrist requiring orthopedic surgery to alleviate the pain and improve mobility.
Bone growth in individuals with dyschondrosteosis should be monitored regularly by a physician during the growth years. In severe cases, surgery may be chosen to equalize the length of the two legs.
Genetic counseling may be of benefit for affected individuals and their families.
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Some children with dyschondrosteosis have been treated with growth hormone (GH) therapy. More research is necessary to determine the long-term safety and effectiveness of growth hormone therapy for individuals with dyschondrosteosis.
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