Achrondroplasia, the most common type of dwarfism, is a condition where a person is disproportionally small in stature due to a failure in growth hormone production. Approximately 1 in 10, 000 people are afflicted by this disease, and it is evident in humans when a mutation in the 4th chromosome either occurs or is inherited.

Typical bone growth occurs when calcium is deposited within the cartilage, hardening into bone. Achrondroplasia affects this process, preventing the lengthening of bones while allowing them to become abnormally thick. This causes people with Achrondroplasia to be smaller in height (the average height for men is 51.8”, while for women it is 48.6” ), with unusually short limbs and a normal sized head. This means that proportionally, the head looks grossly oversized compared to the rest of the body. The nasal bridge appears to be indented, while the forehead is very prominent. The disease also causes the opening at the base of the skull to be smaller then usual, which can affect the flow of fluid between the brain and spinal cord. The result of this is a build up of fluid in the brain, known as hydrocephalus . In addition, the spine tends to narrow towards the lower back, giving the person a “sway back” due to the curvature. Many health problems can result from achrondroplasia, such as a tendency to gain weight, dental problems due to overcrowding of teeth, muscle strain because of disproportional limbs and hearing loss from frequent severe middle ear infections. Achrondroplasia does not affect the mental capacity of the afflicted.

Achrondroplasia is an autosomal dominant disorder, meaning that it only takes on affected parent to pass the disease onto the offspring. If one parent has the mutated gene, there is a 50% chance that the offspring will have achrondroplasia, while if both parents have the disease, there is only a 25% chance . Most of these children, who have “double dominant” achrondroplasia, die within their first year of life. A person cannot have a “little bit” of achrondroplasia – if they inherit the altered gene, they show all of the symptoms of the disease. Interestingly, only 1 in 8 people afflicted with achrondroplasia inherited the disorder – the rest are the result of a new mutation. Achrondroplasia is one of the few genetic disorders where the paternal age increases the frequency in occurrence of the disease. This means that as the father ages, there is an increased probability that his offspring will inherit the mutated achrondroplasia gene (this is interesting because the probability of inheritance is usually dependent on the mother’s age).

Achrondroplasia occurs when either an altered gene is passed onto the offspring or a new mutation occurs. Achrondroplasia arises when the fibroplast growth factor receptor-3 (FGFR3 or ACH) gene, found on the fourth chromosome, mutates. The specifics of the mutation are not yet known, but extensive research is currently under way.

Genetic counseling is currently available to assess the probability of parents have an achrondroplasic child, but no treatment has been developed. People affected by achrondroplasia have a normal lifespan if there are no complications, and there are many organizations that have been founded to help people deal with socially induced psychological trauma.