ACHONDROPLASIA
Achondroplasia is a genetic disorder affecting bone growth that results in disproportionate dwarfism.
- Achondroplasia is the most common form of disproportionate dwarfism, in which the child’s arm and legs are short in proportion to body length.
- In achondroplasia, the bone tissue does not develop properly, especially the long bones of the arms and legs.
- The disorder occurs in one in 15,000 t0 40,000 live birth.
- People who have the disorder are short stature.
- The average height of adult males with the disorder is about 131 centimeters (4ft 4 inches) and for female, average height is 123 centimeters (4ft 1 inches).
- The disorder affects both male and female equally.
CAUSES
During fetal development, much of the skeleton is made up of a tough but flexible tissue known as cartilage, which eventually develops into bone. However, in achondroplasia, the cartilage forms but is unable to develop into bone particularly in the long bones of the arm and legs causing a disproportionate height. This is caused by mutations in the FGFR3 gene (fibroblast growth factor receptor 3). This gene is responsible for making the fibroblast growth receptor 3, a protein that contributes to the production of collagen and other structural materials in the tissues and bones.
When there a mutation in the FGFR3 gene, it causes the protein to change, leaving it either absent or damaged so that it cannot interact with growth factors, eventually leading to complications in bone development.
Achondroplasia can be inherited in an autosomal dominant pattern. In an autosomal dominant disorder, only one copy of the defective gene is needed to be passed down from the parent before a person gets the disorder. Each child in the family, therefore, has a 50% chance of inheriting the gene that causes the disorder.
If one parent has the condition, the child has a 50% chance of getting it.
However, if both parents have the condition, there is a 25% chance of the child not inheriting the condition, a 50% chance of inheriting one defective gene that causes the condition, a 25% chance of inheriting two defective genes resulting in a double dominance. This is a fatal form of achondroplasia called homozygous achondroplasia. Children born with this type are usually stillborn or die within a few months of being born.
Due to spontaneous mutation, people with achondroplasia can be born to parents that do not have the condition.
SYMPTOMS
- Shortened arms, legs, and fingers, especially the upper arms and thighs.
- A short stature that’s is below average for sex and age
- Large head size compared to the body
- Crowded and misaligned teeth
- An abnormally large, prominent forehead
- An abnormal curvature of the spine which may be convex (kyphosis) or concave (lordosis)
- An underdeveloped area of the face between the forehead and the jaw
- Bowed lower legs
- Poor muscle tone and loose joints
- Recurrent ear infections due to narrow passages in the ear
- Sleep apnea
- A flattened nasal bridge
- Flat, short, broad feet
- Hydrocephalus (water in the brain)
DIAGNOSIS AND TREATMENT
Diagnosis can be carried out during pregnancy or after the baby is born.
A prenatal ultrasound can help to detect achondroplasia during pregnancy. The doctor will look for characteristic features of the disorder including hydrocephalus, or an abnormally large head.
If the disorder is suspected, A DNA or genetic test may be ordered. These tests look for the defective gene in a sample of the fluid that surrounds the fetus in the womb (amniotic fluid).
After the baby is done, diagnosis can be made by looking at the baby features.
X-rays can be ordered to measure the length of the baby’s bone, this will aid diagnosis
Blood tests may also be ordered to look for the defective FGFR3 gene.
TREATMENT
There is no cure for achondroplasia.
The doctor will address complications as they arise, such as giving antibiotics for ear infections to prevent hearing loss and surgery in case of kyphosis that does not disappear when the child begins to walk.
Some doctor uses growth hormones to increase the growth rate of a child’s bone.