Chondrodystrophy

Chondrodystrophy
Classification and external resources
ICD-10	Q78.9
ICD-9	756.4
DiseasesDB	2592

Chondrodystrophy (literally, "cartilage mal-development") refers to a skeletal disorder caused by one of myriad genetic mutations that can affect the development of cartilage.^[1]

It is a very general term, and is usually only used in the medical literature when a more precise description of the condition is not available.

Presentation

Chondrodystrophy is characterized by a normal-sized trunk with abnormally shortened limbs and extremities (Dwarfism). Those affected with the disorder often call themselves dwarves, little people or short-statured persons. With the advancements in medicine, there are over 100 specific skeletal dysplasias that have been identified. Chondrodystrophy is found in all races and in both females and male and occurs around 1 in every 25,000 children. Chondrodystrophy and Achondroplasia are the most common forms of genetic hyaline disorders.

Hyaline cartilage caps the long bones and the spinal vertebrae. Most childhood limb growth takes place at the ends of the long bones, not in the shaft. Normally, as a child grows, the most interior portion of the joint cartilage converts into bone, and new cartilage forms on the surface to maintain smooth joints. The old joint margins (edges) reabsorb, so that the overall shape of the joint is maintained as growth continues. Failure of this process throughout the body results in a skeletal dysplasia. It also leads to very early onset of Osteoarthritis, because the defective cartilage is extremely fragile and vulnerable to normal wear and tear.

Causes

It is thought that chondrodystrophy^[2] is actually caused by a autosomal, recessive allele. To avoid a potential "lethal dose," both parents must submit to genetic testing. If a child is conceived with another carrier the outcome may be lethal, or the child may be born with Chondrodystrophy, or Dwarfism.^[3] This means that even though both parents are completely normal in height, the child will have one of the two types of skeletal dysplasia. Type 1 (short trunk dysplasia), the more common of the two, is characterised by a long trunk and extremely shortened extremities. Type 2, Short-limb dysplasia, is characterised by a shortened trunk and normal size extremities. Those affected by Chondrodystrophy may also experience metabolic and hormonal disorders, both of which may be monitored and controlled by hormonal injections.

Inheritance

Chondrodystrophy has an autosomal recessive pattern of inheritance.

Chondrodystrophy is an autosomal recessive disorder, meaning that in order for this disease to be expressed, the affected individual must possess two copies of the allele for the disorder. The inheritance of the Chondrodystrophy gene is as follows:

Let us name the dominant allele for normal stature "T", and the recessive allele coding for Chondrodystrophy "t"; either one or the other is going to be chosen during random selection for a particular "seat" on its chromosome. If both parents are heterozygous for Chondrodystrophy, they each possess one copy of the T allele and one copy of the t allele (each person has 2 copies of every autosomal allele, a paternal and a maternal). When they reproduce there are then four possible alleles that may be chosen at random, two of them are the T allele (one from the father, one from the mother), and two are t alleles (again, one from the father, and one from the mother). The resulting Mendelian ratio of offspring from this mating would then be: 1 homozygous dominant, or TT 2 heterozygous, or Tt 1 homozygous recessive, or tt

The phenotypes of the offspring would be 3 unaffected, normal stature offspring, and one affected Chondrodystrophic offspring; ther would be a 25% chance of having an affected offspring if both parents were carriers of the recessive allele. Other probabilities for the other possible allele combinations concerning this gene are: 0% chance of affected offspring if only one parent is a carrier, 0% chance of affected offspring if one parent is affected and the other doesn't carry the allele, and 50% chance of affected offspring if one parent is affected and the other is a carrier. These ratios may be found by doing a standard Mendelian punnett square.

Percentage Risk of Inheritance

Both Average parents...

1.) A couple already has a child with Chondrodystrophy, the risk of inheritance for the next child to have the disorder is 0.1% (less than 1 in 1,000)

2.) The normal statured child will have at least one offspring with this disorder is 0.01% (less than 1 in 10,000

One parent with Chondrodystrophy and one parent without...

1.) One child with normal height, the probability of that child having offspring with Chondrodystrophy is 0.01% (less than 1 in 10,000)

2.) One child with normal stature, the probability of the next having Chondrodystrophy is 50% (1 in 2)

3.) One child with normal stature, the probability of the next not having Chondrodystrophy is 50% (1 in 2)

Both parents with Chondrodystrophy...

1.) Offspring to be affected by Chondrodystrophy is 100% (4 in 4)

2.) Offspring to be normal size 0% (0 in 4)

Diagnosis

There are several ways to determine if a child has Chondrodystrophy including parent testing and x-rays. If the fetus is suspected of having Chondrodystrophy, the parents can be tested to find out if the fetus in fact does have the disease. It is not until the baby is born that a diagnosis can be declared.^[3] The diagnosis is declared through several x-rays^[4] and charted bone growth patterns. Once the child is diagnosed the parents have to monitor the children because of several different factors. As the child gets older, hearing, eyesight and motor skills may be defective. Also, breathing (apnea) and weight problems (obesity) may occur. Structurally, scoliosis, bowed legs (genu varum), and arthritis may result.

Treatment

There is no treatment at this time to promote actual bone growth in chondrodystrophy patients. Certain types of growth hormone seem to increase the rate of growth during the first year of life/treatment, but has no substantial effect once in adulthood. Only a few surgical centers in the world perform, experimentally, leg and arm lengthening procedures. Most common therapies are found in seeking help from: family physicians, pediatrics, internists, endocrinologists, geneticists, orthopedists and neurologists.

Ways to help/handle/cope with Chondrodystrophy

It is important that the individual feel independence and self-worth. Under the American Constitution, Little People are protected by the Disability discrimination act, even though most little people do not act or feel that they have a disability. There are several appliances made available to help with their stature, including light-switch extender and longer pedals for effective driving purposes. Also, there are several organizations that help Little People interact and get involved, such as the Little People of America.

Physical Education and Sport Program Considerations

Having short limbs can limit ball handling, and athletic performance in racquet sports and certain track events, like the long jump, high jump. However short limbs can be an advantage for a sport like power lifting. Additionally, swimming and bicycling are recommended due to limited impact on their joints.

Modification Suggestions

• Height adjustments for goals and volleyball nets.
• Modified rules to accommodate size and structure.
• Modified equipment such as smaller balls and/or racquets.
• Lowered swings to allow a "feeling" of independence on the playground.

The Dwarf Athletic Association of America

The Dwarf Athletic Association was started in 1985 only for little people. Common sports are basketball, volleyball, powerlifting, track, field, swimming and bowling. National events are held along with the annual conference of Little People of America. The games accommodate athletes who are 4'10" or less with chondrodystrophy or related causes. Also athletes who meet the above requirements compete in the Paralympic Games and other events sponsored by the International Paralympic Committee.

References

1. ^ "Definition: chondrodystrophy from Online Medical Dictionary". http://cancerweb.ncl.ac.uk/cgi-bin/omd?chondrodystrophy. Retrieved 2007-12-23. 
2. ^ "CJO - Abstract - Genetic management of chondrodystrophy in California condors". http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=54889. Retrieved 2007-12-23. 
3. ^ ^{a b} "Dwarfism". http://www.kidshealth.org/parent/growth/growth/dwarfism.html. Retrieved 2007-12-23. 
4. ^ "Dysplasia Epiphysealis Multiplex (DEM) (earlier synonyms: Fairbank's Disease, Ribbing's disease, Epiphyseal dysostosis, Hereditary enchondral dysostosis)". http://www.e-radiography.net/radpath/e/epiphyseal_d.htm. Retrieved 2007-12-23.