Genetic Disorders. Achondroplasia


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Genetic Disorders:

Genetic Disorders Achondroplasia .

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Achondroplasia is a form of short-limbed dwarfism. The word achondroplasia literally means "without cartilage formation." Cartilage is a tough but flexible tissue that makes up much of the skeleton during early development. However, in achondroplasia the problem is not in forming cartilage but in converting it to bone (a process called ossification), particularly in the long bones of the arms and legs. Achondroplasia is similar to another skeletal disorder called hypochondroplasia , but the features of achondroplasia tend to be more severe.

What happens..:

What happens.. Health problems commonly associated with achondroplasia include episodes in which breathing slows or stops for short periods (apnea), obesity, and recurrent ear infections. In childhood, individuals with the condition usually develop a pronounced and permanent sway of the lower back ( lordosis ) and bowed legs. Some affected people also develop abnormal front-to-back curvature of the spine ( kyphosis ) and back pain. A potentially serious complication of achondroplasia is spinal stenosis , which is a narrowing of the spinal canal that can pinch (compress) the upper part of the spinal cord. Spinal stenosis is associated with pain, tingling, and weakness in the legs that can cause difficulty with walking. Another uncommon but serious complication of achondroplasia is hydrocephalus, which is a buildup of fluid in the brain in affected children that can lead to increased head size and related brain abnormalities.

Causes :

Causes Mutations in the  FGFR3  gene cause achondroplasia . The  FGFR3  gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. Two specific mutations in the  FGFR3  gene are responsible for almost all cases of achondroplasia . Researchers believe that these mutations cause the FGFR3 protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.


E pidemiology Achondroplasia is the most common type of short-limbed dwarfism. The condition occurs in 1 in 15,000 to 40,000 newborns . The appropriate identification of lethal skeletal dysplasia is important not only for current pregnancy management but also for genetic counseling concerning future pregnancies. (Table 1) provides the genetic inheritance for a few of the more common skeletal dysplasia .


inheritation Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. About 80 percent of people with achondroplasia have average-size parents; these cases result from new mutations in the  FGFR3  gene. In the remaining cases, people with achondroplasia have inherited an altered  FGFR3  gene from one or two affected parents. Individuals who inherit two altered copies of this gene typically have a severe form of achondroplasia that causes extreme shortening of the bones and an underdeveloped rib cage. These individuals are usually stillborn or die shortly after birth from respiratory failure.


Prevention Achondroplasia can be detected before birth by the use of  prenatal   ultrasound . A DNA test can be performed before birth to detect  homozygosity , wherein two copies of the mutant gene are inherited, a lethal condition leading to stillbirths .

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At present, there is no known treatment for achondroplasia , even though the cause of the mutation in the growth factor receptor has been found. Although used by those without achondroplasia to aid in growth,  human growth hormone  does not help people with achondroplasia . However, if desired, the controversial surgery of  limb-lengthening  will lengthen the legs and arms of someone with achondroplasia . [5] Usually, the best results appear within the first and second year of therapy .  After the second year of GH therapy, beneficial bone growth decreases. [7]  Therefore, GH therapy is not a satisfactory long term treatment. [6]

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Gene based therapy may possibly serve as a future treatment option. BioMarin Pharmaceutical Inc. recently  announced the initiation of a Phase 1 study  in healthy volunteers for BMN-111, an analog of C-type Natriuretic Peptide (CNP), for the treatment of achondroplasia . Latest research and related efforts are tracked by the non-profit  Growing Stronger


Brothers….. Achondroplasia is one of 19 congenital conditions with similar presentations, such as  osteogenesis imperfecta ( Breaking of Bones, Easily.) , multiple epiphyseal dysplasia tarda ,  achondrogenesis ( lack of growth hormone),   osteopetrosis ( bones become denser and harder), and  thanatophoric dysplasia . This makes estimates of prevalence difficult, with changing and subjective diagnostic criteria over time. One detailed and long-running study in the Netherlands found that the prevalence determined at birth was only 1.3 per 100,000 live births. [8]  However, another study at the same time found a rate of 1 per 10,000.



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