ACHONDROPLASIA Literally means “without cartilage formation” Most common type of dwarfism. Caused by mutation of gene for (FGFR3) Average height is about 4 ft. Short arms and legs. Large head.
SIGNS AND SYMTOMS Abnormal hand appearance with persistent space between the longand ring fingers Bowed legs Decreased muscle tone Disproportionately large head-to-body size difference Prominent forehead
Shortened arms and legs (especially the upper arm and thigh) Short stature (significantly below the average height for a personof the same age and sex) Spinal stenosis Spine curvatures called kyphosis and lordosis
PATHOGENESIS The gene affected is the Fibroblast Growth Factor Receptor 3 Gene. Achondroplasia gene was mapped near the telomere of the short armof chromosome 4. The FGFR3 protein is involved in the development and maintainanceof bone and brain tissue. Receptor regulates bone growth by limiting the formation of bonefrom cartilage in the long bones.
DENTAL CORRELATION The administration of thyroid hormone is known to acceleratedental development and eruption. his dental development is still extremely retarded and is followinga disturbed pattern in which various stages of dental development arepresent simultaneously.
For example, he shows absence of resorption of the deciduouscanine and deciduous molar roots, which is found in children fromthe age of 8 onward. The permanent second molars, which usuallyare erupted at the age of 12 years, are still unerupted and have corticalbone overlying their occlusal surfaces. This is usually not found after the age of 12 years. To the contrary,the third molars are located in the body of the mandible, which is notfrequently seen before the age of 15 years.
MENDELIAN It is inherited as a mendelian autosomal dominant trait withcomplete penetrance. Approximately 80% of cases are due to new orde novo dominant mutations with a mutation rate estimated to be0.000014 per gamete per generation.
SINGLE GENE It is single gene because it only affects the Fibroblast GrowthFactor Receptor 3 Gene which is responsible for the maintenace ofbone and brain tissue.