Achondroplasia takes its name from three Greek roots—a (without), chondros (cartilage), and plasis (formation)—and refers to impaired development of the growth cartilage in the long bones of the limbs. In children, this cartilage has not yet fused to bone; it is what allows bones to lengthen as we grow.
Achondroplasia affects roughly one in 20,000 newborns. In 90 percent of cases, it appears as a sporadic mutation in the sperm or egg of unaffected parents. The child with achondroplasia is born to a healthy couple with no family history, and the chance of a second affected child is negligible. In the remaining 10 percent, the condition is inherited as an autosomal dominant trait: one affected parent carries the disease gene and passes it to each child with a 50 percent probability per pregnancy. When both parents have achondroplasia, the odds shift: there is a 50 percent chance the child inherits the gene from one parent only (heterozygous form); a 25 percent chance of inheriting it from both (homozygous, a more severe form); and a 25 percent chance of inheriting it from neither and being unaffected. In short, when both parents are affected, there is a 75 percent chance their child will have the condition.
Read also: Salvatore, pediatrician with achondroplasia
The mutated gene in achondroplasia is located on the short arm of chromosome 4. This makes early prenatal diagnosis possible for couples at risk—those with at least one affected partner—through DNA analysis. This test is the first step toward understanding the gene's precise function and, eventually, developing targeted therapy (though such treatments are still years away).
Achondroplasia presents as disproportionate short stature: the ratio of trunk to limbs is altered. The trunk is normal length, but the limbs are shortened, particularly in the portions closer to the body.
At birth, an infant with achondroplasia is roughly the same height and weight as any other newborn. Height remains similar to that of unaffected children through the first year of life. After that, the growth lag becomes visible.
Average adult height reaches about 130 centimeters (roughly 4'3"). Head circumference, which is larger than normal at birth, grows more rapidly in the first year and then levels off.
The most common complications are orthopedic: excessive curvature of the upper spine (kyphosis), excessive curvature of the lower spine (lordosis), and bowing of the legs. Neurological problems—hydrocephalus and spinal cord compression in the neck or lower back—are rarer. Importantly, achondroplasia does not cause intellectual disability.
The most practical way to improve quality of life is surgical limb lengthening, a procedure typically begun between ages three and fourteen. Surgery extends both the thighbones and shinbones; each segment gains roughly 10 centimeters. This can bring final height to over 150 centimeters (5 feet) and restore independence in everyday tasks—using an elevator, boarding public transport, and much more. Upper limb lengthening is also possible.
These techniques require long periods of relative immobility and place substantial physical and psychological demands on the patient and family alike.
Salvatore Anastasi, 2007
Senior Pediatrician, Thalassemia Unit, Garibaldi Hospital, Catania; Councilor for Public Works and Vice Mayor, San Giovanni La Punta