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Ancestor membership does not transfer phenotype values between groups.","importantHtml":""},"sections":[{"bodyHtml":"

The vast majority of cases of hypochondroplasia are caused by variants in the FGFR3 gene. This gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. Although it remains unclear how FGFR3 gene variants lead to the features of hypochondroplasia, researchers believe that these genetic changes cause the protein to be overly active. The overactive FGFR3 protein likely interferes with skeletal development and leads to the disturbances in bone growth that are characteristic of this disorder.

Some people with hypochondroplasia do no have a variant in the FGFR3 gene. Researchers suspect that variants in other genes cause hypochondroplasia in these people, although these genes have not been identified.

MedlinePlus Genetics: Causes

","key":"forms","title":"What causes Hypochondroplasia?"},{"bodyHtml":"

All people with hypochondroplasia have short stature. The adult height for men with this condition ranges from 138 centimeters to 165 centimeters (4 feet, 6 inches to 5 feet, 5 inches). The height range for adult women is 128 centimeters to 151 centimeters (4 feet, 2 inches to 4 feet, 11 inches).

People with hypochondroplasia have short arms and legs and broad, short hands and feet. Other characteristic features include a a large head (macrocephaly), limited range of motion at the elbows, a sway of the lower back (lordosis), and bowed legs. These signs are generally less pronounced than those seen in people with achondroplasia and may not be noticeable until early or middle childhood. Affected individuals have a small increased risk of a seizure disorder known as temporal lobe epilepsy. Some studies have reported that a small percentage of people with hypochondroplasia have mild to moderate intellectual disability or learning problems, but other studies have produced conflicting results.

Source: MedlinePlus Genetics

","key":"overview","title":"Condition overview"}],"sharedSources":[],"slug":"hypochondroplasia","sourceDocuments":[{"name":"Hypochondroplasia","reviewed":"2023-06","sections":{"causes":{"fetchedAt":"2026-10-20T20:22:21.157306+00:00","label":"Causes","pageSha256":"8623f84d0d0dfb4c1904fefbd37c030c902194a8a7b22b155cd61a61cac9160a","sourceUrl":"https://medlineplus.gov/genetics/condition/hypochondroplasia/#causes","status":"available"}},"source_release":"2026-10-01","url":"https://medlineplus.gov/genetics/condition/hypochondroplasia"}],"sourceNote":"MedlinePlus descriptions and Causes; original HPO annotations.","takeawayHtml":"Cause explanations are from MedlinePlus Genetics. Feature values below retain their original sources and patient groups.","title":"Hypochondroplasia"},"schemaVersion":1}