auses: Achondroplasia: Growth plate cartilage in the long bones is converted to bone too early in development.
Although this condition can be inherited in an autosomal dominant manner, 80% of cases are due to new, sporadic mutations. Mutations involve the gene encoding fibroblast growth factor receptor 3 (FGFR3), situated on chromosome 4. Most commonly, a point mutation causes the substitution of arginine for glycine (G380R) in the transmembrane region of the receptor. (Source: Genes and Disease by the National Center for Biotechnology)

Answered by Vikas Mor , an ibibo Citizen, at 4:57 PM on October 11, 2008

Hi Kailash,

Achondroplasia is a result of an autosomal dominant mutation in the fibroblast growth factor receptor gene 3 (FGFR3), which causes an abnormality of cartilage formation. FGFR3 normally has a negative regulatory effect on bone growth. In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones.

Animals with achondroplasia have one normal copy of the fibroblast growth factor receptor 3 gene and one mutant copy. Two copies of the mutant gene are invariably fatal before, or shortly after birth. Only one copy of the gene needs to be present for the disorder to occur. Therefore, a person with achondroplasia has a 50% chance of passing on the gene to their offspring, meaning that there will be a 50% chance that each child will have achondroplasia. Since two copies (Homozygous) are fatal, if two people with achondroplasia have a child, there is a 25% chance of the child dying shortly after birth, a 50% chance the child will have achondroplasia, and a 25% chance the child will have a normal phenotype. However, in the majority of cases, people with achondroplasia are born to parents who don't have the condition. This is the result of a new mutation.[3]

New gene mutations are associated with increasing paternal age[4] (over 35 years). Studies have demonstrated that new gene mutations are exclusively inherited from the father and occur during spermatogenesis (as opposed to resulting from a gonadal mosaicism). More than 99% of achondroplasia is caused by two different mutations in the fibroblast growth factor receptor 3 (FGFR3). In about 98% of cases, a G to A point mutation at nucleotide 1138 of the FGFR3 gene causes a glycine to arginine substitution (Bellus et al 1995, Shiang et al 1994, Rousseau et al 1996). About 1% of cases are caused by a G to C point mutation at nucleotide 1138.

There are two other syndromes with a genetic basis similar to achondroplasia: hypochondroplasia and thanatophoric dysplasia.

Source site :

http://en.wikipedia.org/wiki/A chondroplasia

Answered by Priyanka C , an ibibo Master, at 4:46 PM on October 11, 2008

Most people with achondroplasia have average-size parents, which mean that the cause of achondroplasia is from a new mutation in the FGFR3 gene. Scientists do not know why this mutation occurs.

Achondroplasia is inherited by an autosomal dominant gene that causes abnormal cartilage formation. Autosomal dominant inheritance means that the gene is located on one of the autosomes (chromosome pairs 1 through 22). This means that males and females are equally affected.

Caused by autosomal dominant genetic(it means if fathers have who is in 45 years old) and affected by incomplite bone growth.

Adolescents and adults with achondroplasia often develop weakness, tingling and pain in the legs or low back pain. This is often due to pressure on the spinal cord from a small spinal canal.

When a parent has a dominant trait, there is a 50 percent chance that any child they have will also inherit the trait. So, in some cases, the child inherits the achondroplasia from a parent with achondroplasia. The majority of achondroplasia cases (80 percent), however, are the result of a new mutation in the family - the parents are of average height and do not have the abnormal gene.

Answered by Yogeshwar , an ibibo Specialist, at 4:36 PM on October 11, 2008

Achondroplasia is inherited by an autosomal dominant gene that causes abnormal cartilage formation. Autosomal dominant inheritance means that the gene is located on one of the autosomes (chromosome pairs 1 through 22). This means that males and females are equally affected. Dominant means that only one gene is necessary to have the trait. When a parent has a dominant trait, there is a 50 percent chance that any child they have will also inherit the trait. So, in some cases, the child inherits the achondroplasia from a parent with achondroplasia. The majority of achondroplasia cases (80 percent), however, are the result of a new mutation in the family - the parents are of average height and do not have the abnormal gene.

As mentioned, persons with achondroplasia have a 50 percent chance to pass the gene to a child, resulting in the condition. If both parents have achondroplasia, with each pregnancy, there is a 50 percent chance to have a child with achondroplasia, a 25 percent chance that the child will not inherit the gene and be of average height, and a 25 percent chance that the child will inherit one abnormal gene from each parent, which can lead to severe skeletal problems that often result in early death.

Geneticists have found that fathers who are older than 45 have a higher chance of having children with certain autosomal dominant conditions such as achondroplasia, but no cause for the new mutations in sperm has been discovered at this time.

The gene responsible for achondroplasia was discovered in 1994 making accurate prenatal diagnosis available, in most cases.

Answered by Vinay Kiran , an ibibo Specialist, at 3:21 PM on October 11, 2008

Mutations (chemical changes) within a single gene cause achondroplasia. The condition may be passed on from one generation to the next or it may result from a new mutation in a gene from average-sized parents.

Answered by Alok , an ibibo Master, at 2:41 PM on October 11, 2008