Diagnosis
Achondroplasia can be detected before birth by prenatal ultrasound, although signs are often subtle and not apparent before the 24th week of pregnancy. A DNA test can be performed before birth to detect homozygosity, wherein two copies of the mutant gene are inherited, a lethal condition leading to stillbirths. Postnatal diagnosis of achondroplasia is typically uncomplicated, involving an assessment of physical and radiographic features. Clinical features include megalocephaly, short limbs, prominent forehead, thoracolumbar kyphosis and mid-face hypoplasia. Complications like dental malocclusion, hydrocephalus and repeated otitis media can be observed. The risk of death in infancy is increased due to the likelihood of compression of the spinal cord with or without upper airway obstruction. Radiologic findings
A skeletal survey is useful to confirm the diagnosis of achondroplasia. The skull is large, with a narrow foramen magnum, and relatively small skull base. The vertebral bodies are short and flattened with relatively large intervertebral disk height, and there is congenitally narrowed spinal canal. The iliac wings are small and squared, with a narrow sciatic notch and horizontal acetabular roof. The tubular bones are short and thick with metaphyseal cupping and flaring and irregular growth plates. Fibular overgrowth is present. The hand is broad with short metacarpals and phalanges, and a trident configuration. The ribs are short with cupped anterior ends. If the radiographic features are not classic, a search for a different diagnosis should be entertained. Because of the extremely deformed bone structure, people with achondroplasia are often "double jointed".
People with achondroplasia are often born to parents that do not have the condition due to spontaneous mutation.Achondroplasia can be inherited through autosomal dominance. In couples where one partner has achondroplasia there is a 50% chance of passing the disorder on to their child every pregnancy. In situations where both parents have achondroplasia there is a 50% chance the child will have achondroplasia, 25% chance the child will not, and a 25% chance that the child will inherit the gene from both parents resulting in double dominance and leading to severe or lethal bone dysplasia.Studies have demonstrated that new gene mutations for achondroplasia are exclusively inherited from the father and occur during spermatogenesis; it has been theorized that sperm carrying the mutation in FGFR3 have a selective advantage over sperm with normal FGFR3. The frequency of mutations in sperm leading to achondroplasia increases in proportion to paternal age, as well as in proportion to exposure to ionizing radiation. The occurrence rate of achondroplasia in the children of fathers over 50 years of age is 1 in 1,875, compared to 1 in 15,000 in the general population. Research by urologist Harry Fisch of the Male Reproductive Center at Columbia Presbyterian Hospital in 2013 indicated that in humans this defect may be exclusively inherited from the father and becomes increasingly probable with paternal age, specifically males reproducing after 35.There are two other syndromes with a genetic basis similar to achondroplasia: hypochondroplasia and thanatophoric dysplasia.