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Chondrodystrophy (literally, "cartilage maldevelopment") refers to a
skeletal disorder A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fram ...
caused by one of myriad genetic mutations that can affect the development of
cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...
. As a very general term, it is only used in the medical literature when a more precise description of the condition is unavailable.


Presentation

People with chondrodystrophy have a normal-sized trunk and abnormally short limbs and extremities (
dwarfism Dwarfism is a condition of people and animals marked by unusually small size or short stature. In humans, it is sometimes defined as an adult height of less than , regardless of sex; the average adult height among people with dwarfism is . '' ...
). Those affected with the disorder often call themselves dwarves, little people or short-statured persons. Over 100 specific skeletal dysplasias have been identified. Chondrodystrophy is found in all races and in both females and male and occurs in around one of every 25,000 children. Chondrodystrophy and
achondroplasia Achondroplasia is a genetic disorder with an autosomal dominant pattern of inheritance whose primary feature is dwarfism. It is the most common cause of dwarfism and affects about 1 in 27,500 people. In those with the condition, the Rhizomeli ...
are the most common forms of genetic hyaline disorders. Hyaline cartilage caps the long
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
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 skeletal dysplasia. It also leads to very early onset of
osteoarthritis Osteoarthritis is a type of degenerative joint disease that results from breakdown of articular cartilage, joint cartilage and underlying bone. A form of arthritis, it is believed to be the fourth leading cause of disability in the world, affect ...
, because the defective cartilage is extremely fragile and vulnerable to normal wear and tear.


Causes

It is thought that chondrodystrophy is caused by an
autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosome ...
, recessive allele. To avoid a potential "lethal dose", both parents can be genetically tested. If a child is conceived with another carrier the outcome may be lethal, or the child may suffer from 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 limb dysplasia), the more common of the two, is characterised by a long trunk and extremely shortened extremities. Type 2, short-trunk 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. Animals have been bred specifically to elicit chondrodystrophic traits for research purposes and to more easily allow animals to free-roam without escaping by, for example, jumping over ranch fences. One example of this is the
Ancon sheep Ancon sheep (also called "Otter" sheep) were a grouping of domestic sheep with long bodies and very short legs, with the fore-legs being crooked. The term is generally applied to a line of sheep bred from a single affected lamb born in 1791 in Mas ...
, which was first bred from a lamb born in 1791 with naturally occurring chondrodystrophy.


Inheritance

Chondrodystrophy is an
autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...
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 two copies of every autosomal allele, a paternal and a maternal one). 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 three unaffected, normal-stature offspring, and one affected chondrodystrophic offspring; there 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 does not 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 drawing up a standard Mendelian punnett square.


Percentage risk of inheritance

* Both average parents *# 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) *# The risk that 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 *# One child with normal height; the probability of that child having offspring with chondrodystrophy is 0.01% (less than 1 in 10,000) *# One child with normal stature; the probability of the next having chondrodystrophy is 50% (1 in 2) *# One child with normal stature; the probability of the next not having chondrodystrophy is 50% (1 in 2) * Both parents with chondrodystrophy *# The probability of offspring affected by chondrodystrophy is 100% (4 in 4) *# The probability of offspring to be of normal size is 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 with the help of 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 (
apnea Apnea (also spelled apnoea in British English) is the temporary cessation of breathing. During apnea, there is no movement of the muscles of inhalation, and the volume of the lungs initially remains unchanged. Depending on how blocked the ...
) and weight problems (
obesity Obesity is a medical condition, considered by multiple organizations to be a disease, in which excess Adipose tissue, body fat has accumulated to such an extent that it can potentially have negative effects on health. People are classifi ...
) may occur. Structurally,
scoliosis Scoliosis (: scolioses) is a condition in which a person's Vertebral column, spine has an irregular curve in the coronal plane. The curve is usually S- or C-shaped over three dimensions. In some, the degree of curve is stable, while in others ...
, bowed legs (
genu varum Genu varum (also called bow-leggedness, bandiness, bandy-leg, and tibia vara) is a varus deformity marked by (outward) bowing at the knee, which means that the lower leg is angled inward ( medially) in relation to the thigh's axis, giving th ...
), and
arthritis Arthritis is a general medical term used to describe a disorder that affects joints. Symptoms generally include joint pain and stiffness. Other symptoms may include redness, warmth, Joint effusion, swelling, and decreased range of motion of ...
may result.


Treatment

There is no treatment at this time to promote 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 have no substantial effect in adult patients. 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 physician Family medicine is a medical specialty that provides continuing and comprehensive health care for the individual and family across all ages, genders, diseases, and parts of the body. The specialist, who is usually a primary care physician, i ...
s,
pediatrics Pediatrics (American English) also spelled paediatrics (British English), is the branch of medicine that involves the medical care of infants, children, Adolescence, adolescents, and young adults. In the United Kingdom, pediatrics covers many o ...
,
internist Internal medicine, also known as general medicine in Commonwealth nations, is a medical specialty for medical doctors focused on the prevention, diagnosis, and treatment of diseases in adults. Its namesake stems from "treatment of diseases of th ...
s,
endocrinologist Endocrinology (from ''endocrine'' + '' -ology'') is a branch of biology and medicine dealing with the endocrine system, its diseases, and its specific secretions known as hormones. It is also concerned with the integration of developmental events ...
s,
geneticist A geneticist is a biologist or physician who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a scientist or a lecturer. Geneticists may perform general research on genetic process ...
s,
orthopedist Orthopedic surgery or orthopedics ( alternative spelling orthopaedics) is the branch of surgery concerned with conditions involving the musculoskeletal system. Orthopedic surgeons use both surgical and nonsurgical means to treat musculoskeletal ...
s and
neurologists Neurology (from , "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the nervous system, which comprises the brain, the s ...
.


Coping with chondrodystrophy

It is important that the individual experience independence and self-worth. There are several appliances available to help overcome the disadvantages of small stature, including light-switch extenders and longer pedals in cars to enable effective driving. Several organizations that help Little People interact and get involved, such as the
Little People of America Little People of America (LPA) is a 501(c)(3) non-profit organization which provides support, resources, and information to individuals with dwarfism and their families. Founding LPA was founded in 1957 by actor Billy Barty when he informally ca ...
.


Physical education and sports

Having short limbs can limit ball handling, and athletic performance in racquet sports and certain track events, like the long jump and high jump. However, short limbs can be an advantage for a sport like power lifting. Additionally, swimming and bicycling are recommended due to their limited impact on the 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 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 disorders. Athletes who meet the above requirements may compete in the Paralympic Games and other events sponsored by the International Paralympic Committee.


See also

*
Chondrodysplasia An osteochondrodysplasia,Etymology: . or skeletal dysplasia, is a disorder of the development of bone and cartilage. Osteochondrodysplasias are rare diseases. About 1 in 5,000 babies are born with some type of skeletal dysplasia. Nonetheless, if t ...


References


External links

{{Osteochondrodysplasia Skeletal disorders Autosomal recessive disorders