Achondroplasia

Achondroplasia is a bone disorder caused by a mutation in the FGFR3 gene, which normally restrains bone growth. When mutated, it excessively inhibits cartilage-to-bone conversion in the growth plates of the long bones. The result is shortened limbs with relatively normal trunk length, and abnormal growth of the skull base and spine.

About 20–50% of children with achondroplasia develop neurological complications. As the child grows faster than bone growth allows, the narrowed foramen magnum (the opening at the skull base) and small vertebral canals compress the brainstem, spinal cord, spinal nerve roots, and cerebrospinal fluid (CSF) spaces — eventually causing neurological deficits.

**Common symptoms include:** - Shortened arms and legs, with the upper arms and thighs more shortened than forearms and lower legs - Large head with prominent forehead and flattened nasal bridge - Crowded or misaligned teeth - Curved lower spine (lordosis), which may progress to kyphosis with a small shoulder hump that typically resolves once the child walks - Small vertebral canals, risking spinal cord compression in adolescence — and rarely, sudden death in infancy from upper spinal cord compression during sleep - Bowed lower legs - Short, broad flat feet - Extra space between the middle and ring fingers (trident hand) - Poor muscle tone and loose joints - Recurrent middle ear infections, sometimes causing hearing loss - Normal intelligence - Delayed walking (18–24 months rather than ~12 months)

**Treatment** centres on managing neurological complications. When dangerous compression of the foramen magnum or spinal column is found, surgical decompression — removing bone and ligaments — creates more room for neural structures without compromising structural integrity. Because children continue to grow, repeat decompressions may be needed. Early intervention yields the best outcomes: symptoms allowed to progress for months or years may become permanent.

If hydrocephalus develops, a paediatric neurosurgeon may place a ventriculoperitoneal (VP) shunt — a long thin tube running from the brain's ventricles under the skin to the abdomen — to drain CSF at a controlled rate. With timely diagnosis and treatment, achondroplastic children can develop intellectual and social capacities equivalent to other children.