2. 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.
3. SIGNS AND SYMTOMS
Abnormal hand appearance with persistent space between the long
and ring fingers
Bowed legs
Decreased muscle tone
Disproportionately large head-to-body size difference
Prominent forehead
4. Shortened arms and legs (especially the upper arm and thigh)
Short stature (significantly below the average height for a person
of the same age and sex)
Spinal stenosis
Spine curvatures called kyphosis and lordosis
5. PATHOGENESIS
The gene affected is the Fibroblast Growth Factor Receptor 3 Gene.
Achondroplasia gene was mapped near the telomere of the short arm
of chromosome 4.
The FGFR3 protein is involved in the development and maintainance
of bone and brain tissue.
Receptor regulates bone growth by limiting the formation of bone
from cartilage in the long bones.
6.
7. DENTAL CORRELATION
The administration of thyroid hormone is known to accelerate
dental development and eruption.
his dental development is still extremely retarded and is following
a disturbed pattern in which various stages of dental development are
present simultaneously.
8. For example, he shows absence of resorption of the deciduous
canine and deciduous molar roots, which is found in children from
the age of 8 onward. The permanent second molars, which usually
are erupted at the age of 12 years, are still unerupted and have cortical
bone 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 not
frequently seen before the age of 15 years.
9. MENDELIAN
It is inherited as a mendelian autosomal dominant trait with
complete penetrance. Approximately 80% of cases are due to new or
de novo dominant mutations with a mutation rate estimated to be
0.000014 per gamete per generation.
10. SINGLE GENE
It is single gene because it only affects the Fibroblast Growth
Factor Receptor 3 Gene which is responsible for the maintenace of
bone and brain tissue.
