Hypochondroplasia

 Hypochondroplasia

Overview

Hypochondroplasia is a type of skeletal dysplasia or a condition that affects cartilage. Cartilage is connective tissue that protects your bones. It results in short-limbed dwarfism.

For hypochondroplasia, a genetic change prevents cartilage from turning into bone (ossification) in the long bones in your arms and legs.

Physical characteristics of the condition include short stature, bowed legs and broad hands and feet along with a larger head size. Symptoms are rarely noticeable until toddlerhood to early school-age years.

The exact frequency of hypochondroplasia is unknown. Studies show that hypochondroplasia may occur at a similar rate as achondroplasia, which is a more severe form of the condition. The estimated rate of occurrence is 1 in 15,000 to 40,000 newborns around the world

Symptoms

Several physical characteristics lead to a hypochondroplasia diagnosis. Symptoms vary from person to person and could include:

Short stature.

Large head.

Short arms and legs.

Broad hands and feet.

Limited range of motion in the elbows.

Bowed legs.

Inward curve of your spine at the lower back (lordosis).

Growth (height) tends to decrease in toddlerhood to early school-age years. The average height for an adult diagnosed with hypochondroplasia is 138 cm (centimeters) to 165 cm (54 inches to 65 inches tall) for people assigned male at birth (AMAB) and 128 cm to 151 cm (50 in to 59 in tall) for people assigned female at birth (AFAB).

You may experience joint pain in your arms and legs during your lifetime, especially after exercise or physical activity.

Although rare, fewer than 10% of people diagnosed with hypochondroplasia have mild intellectual challenges and problems learning through childhood and adolescence. Hypochondroplasia doesn’t usually affect your intelligence.

Causes

A genetic change (mutation) causes hypochondroplasia. Almost all cases occur because of a genetic change of the FGFR3 gene. The FGFR3 gene is responsible for creating a protein that develops and maintains how bones grow, especially during the conversion of cartilage (the soft connective tissue between bones) into bone. When the FGFR3 gene changes, proteins become overactive and can’t do their job to help bones grow and develop.

You can inherit hypochondroplasia in an autosomal dominant pattern. This means that only one biological parent needs to pass the gene change on to their child during conception to inherit it. So if one parent has it, there’s a 50% chance to pass it on. But most genetic mutations of the FGFR3 gene occur randomly, without being present in a person’s family history (de novo).

A small minority of cases of hypochondroplasia occur without a mutation of the FGFR3 gene. The cause is likely from a mutation of another, unidentified gene.

Diagnosis

A healthcare provider will diagnose hypochondroplasia after your baby is born. This happens because evidence of the condition isn’t always noticeable during a pregnancy ultrasound. If a birthing parent has hypochondroplasia and the genetic cause is known, CVS (chorionic villus sampling) or amniocentesis would be options to diagnose the condition during pregnancy.

After birth, your provider will perform a physical examination of your child, along with a genetic test to pinpoint the gene that is responsible for symptoms.

Your healthcare provider will offer several tests to confirm the diagnosis of hypochondroplasia, including:

An X-ray to examine bone growth.

Genetic tests to identify the genetic mutation responsible for symptoms.

MRI (magnetic resonance imaging) or CT scan (computed tomography scan) to identify spinal curves or compression.

Treatment

Treatment addresses the symptoms of hypochondroplasia that may lead to complications, like abnormal bone growth. Treatment is different for each person and could include:

Vertebrae surgery (laminectomy and decompression) to treat lumbar or lower back nerve compression (stenosis).

Physical therapy to improve mobility and range of motion.

Growth hormone treatment.

Medications for joint pain.

Some families and people diagnosed with hypochondroplasia benefit by joining support groups to talk about their (or their child’s) diagnosis among peers who share a similar experience. Support groups offer helpful information like education on employment, disability rights and parenting.

Type of Doctor Department: An orthopedic surgeon, Neurologist/Neurosurgeon