Chondrodystrophy

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Overview

Chondrodystrophy (literally, "cartilage bad-nourishment") is a descriptive term no longer in use in the medical literature. It refers to a skeletal disorder caused by one of myriad genetic mutations that can affect hyaline cartilage. This genetic disorder is characterized by a normal size trunk with shortened limbs and extremities. These are characteristics of Dwarfism. People that suffer from this 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. The disease is found in all races and in both females and male and occurs around 1 in every 25,000 children. Besides Chondrodystrophy, Achondroplasia is the most common.

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.

It is thought that Condrodystrophy is actually caused by a autosomal, recessive allele. The best possible way to avoid a "lethal dose" of the disease is knowing if you are a carrier, and if you are, not conceiving with a fellow carrier. If you do conceive with another carrier the outcome is lethal, creating Chondrodystrophy, or Dwarfism. This means that even though both parents are completely normal in height, the child will be one of the two types of skeletal dysplasia. Type 1, is short trunk dysplasia, the more common of the two, with characteristics or a long trunk and extremely shortened extremities. Type 2, Short-limb dysplasia, shows a shortened trunk and normal size extremities. People with Chondrodystrophy not only have abnormal frames, but also may experience metabolic and hormonal disorders, both of which are monitored and controlled by hormonal injections. Unfortunately, because of their short stature many also experience whole system failures such as hearing, sight and digestive.

Inheritance

Chondroplasia is believed to be 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 Chondroplasia gene is as follows:

Let us name the dominant allele for normal stature "T", and the recessive allele coding for Chondroplasia "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 Chondroplasia, they each posess 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 Chondroplasiac offspring; ther would be a twenty-five% 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 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 probablity of the next having Chondrodystrophy is 50% (1 in 2)

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

Both parents with Chondrodystrophy...

1.) Offspring to inherit a single copy of the Chondrodystrophy gene is 50% (1 in 2)

2.) Offspring to be normal size 25% (1 in 4)

3.) Offspring inherit lethal does of Chondrodystrophy gene is 25% (1 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. The diagnosis is declared through several x-rays 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, eye sight 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 thistime 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, experiementally, leg and arm lengthening procedures. Most common therapies are found in seeking help from: family physicans, 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 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 choldrodystrophy or related causes. Also athletes who meet the above requirements compete in the Paralympic Games and other events sponsored by the International Paralympic Committee.




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