Chondrodystrophy
Encyclopedia
Chondrodystrophy refers to a skeletal disorder caused by one of myriad genetic mutations that can affect the development of cartilage
.
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.
). 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 bone
s 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.
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.
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)
) and weight problems (obesity
) may occur. Structurally, scoliosis
, bowed legs (genu varum), and arthritis
may result.
, internists, endocrinologists, geneticist
s, orthopedists and neurologists.
, 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
.
Cartilage
Cartilage is a flexible connective tissue found in many areas in the bodies of humans and other animals, including the joints between bones, the rib cage, the ear, the nose, the elbow, the knee, the ankle, the bronchial tubes and the intervertebral discs...
.
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 (DwarfismDwarfism
Dwarfism is short stature resulting from a medical condition. It is sometimes defined as an adult height of less than 4 feet 10 inches , although this definition is problematic because short stature in itself is not a disorder....
). 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
Achondroplasia
Achondroplasia dwarfism occurs as a sporadic mutation in approximately 85% of cases or may be inherited in an autosomal dominant genetic disorder that is a common cause of dwarfism...
are the most common forms of genetic hyaline disorders.
Hyaline cartilage caps the long bone
Bone
Bones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
s 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
Osteoarthritis
Osteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
, because the defective cartilage is extremely fragile and vulnerable to normal wear and tear.
Causes
It is thought that chondrodystrophy 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. 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
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. 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, eyesight and motor skills may be defective. Also, breathing (apneaApnea
Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...
) and weight problems (obesity
Obesity
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health, leading to reduced life expectancy and/or increased health problems...
) may occur. Structurally, scoliosis
Scoliosis
Scoliosis is a medical condition in which a person's spine is curved from side to side. Although it is a complex three-dimensional deformity, on an X-ray, viewed from the rear, the spine of an individual with scoliosis may look more like an "S" or a "C" than a straight line...
, bowed legs (genu varum), and arthritis
Arthritis
Arthritis is a form of joint disorder that involves inflammation of one or more joints....
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, pediatricsPediatrics
Pediatrics or paediatrics is the branch of medicine that deals with the medical care of infants, children, and adolescents. A medical practitioner who specializes in this area is known as a pediatrician or paediatrician...
, internists, endocrinologists, geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
s, 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 actDisability discrimination act
In the late 20th and early 21st centuries, a number of countries have passed laws aimed at reducing discrimination against people with disabilities. These laws have begun to appear as the notion of civil rights has become more influential globally, and follow other forms of anti-discrimination and...
, 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
Little People of America
Little People of America is a non-profit organization which provides support, resources and information to individuals with dwarfism and their families...
.
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.