Hypochondroplasia

Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at September 6, 2016
StartDiseasesHypochondroplasia

Hypochondroplasia is a congenital disorder characterized by very short stature. Estimates say that approximately one in 15,000 infants are born with hypochondroplasia.

Contents

Definition & Facts

Hypochondroplasia is a rare genetic disorder and a form of dwarfism. The word means 'low cartilage growth'. Genetic mutations affect embryonic development by interfering with cell division. The disorder prevents lengthening of the long bones, resulting in short stature and a large head.

Short arms and legs and broad hands and feet are characteristics of the condition, as well as a limited range of motion in elbow and hip joints. The lower back may be swayed (lordosis) and legs bowed.

If one parent has hypochondroplasia, children are 50 percent likely to be affected. A child with two parents who have the condition may be severely affected. Females and males are equally at risk. Small percentages of people with hypochondroplasia (about 10 percent) have mild intellectual disabilities.

Symptoms & Complaints

Shortening of limbs may be mild to severe. Children at birth seem to progress normally, and slow growth may not be much of a factor. At the ages of about two or three, the condition is usually noted, but sometimes the symptoms are not recognized until young adulthood.

Bowing of the legs is obvious during early childhood, but the condition may improve spontaneously later on. Affected children may have limitations in elbow and hip movement. Minor joint aches can occur when these joints are overused, as in a long day of walking or sports. Sometimes the pain radiates to the lower back due to the curved lower spine.

Tooth eruption may be compromised by malocclusion due to cranial malformations or jaw malformations. These deformities may result in speech problems. Facial appearance is generally normal, but some persons have an abnormally-sized head or a very broad short skull with a large forehead. Adult height is, on average, between 4 feet 6 inches (1.37 meters) and 4 feet 11 inches (1.49 meters).

Causes

Most cases of hypochondroplasia are caused by mutations in the FGFR3 gene. This gene is involved in the production of a protein responsible for bone and cartilage development. It is passed down through autosomal dominant inheritance. Researchers have noted that, in some instances, children of older fathers are affected.

Sometimes hypochondroplasia seems to appear randomly, with no apparent family history of the condition. Specific, complex gene mutations can suddenly occur within parents of average stature.

To complicate things further, different mutations of the same genes may present with hypochodroplasia. Much research is needed to detect the multiple, underlying factors of this condition.

Diagnosis & Tests

The diagnosis of hypochondroplasia is made upon a physical examination and physical observation. X-rays and other medical imaging studies may be used to verify the observations. Early diagnosis is very important because orthopedic measures can be taken that greatly improve quality of life and increase potential for children with the disorder.

Height, weight and head circumference should be regularly assessed using standardized growth charts for hypochondroplasia. Neurological examinations to assess signs of spinal cord compression are vital to mobility. A history of central sleep apnea can be an indication of spinal cord compression.

Treatment & Therapy

There is no cure for short stature, and treatments are directed toward symptoms that each individual may present. Skeletal abnormalities cause discomfort and limitations in mobility. Orthopedic treatment such as surgery may be indicated to relieve conditions like spinal stenosis, which is a serious and progressive narrowing of the spinal canal.

Human growth hormone therapy has proven to be efficacious in some situations, lengthening the spinal column. Surgical lengthening of arms and legs, a long and uncomfortable process is sometimes opted. If a child fails to begin an adolescent growth spurt, human growth hormone can restore functioning. Severely small children may need treatment before puberty, as well.

Because clinical cranial manifestations of hypochondroplasia may result in crowded teeth and tooth decay due to crowded conditions, some teeth facilitate an even dental structure.

If there are cognitive deficits, special education programs should be implemented. Social adjustment is a concern as well. Adult females with hypochondroplasia wishing to become pregnant should be examined for pelvic outlet capacity and for their spinal anatomy, as spinal stenosis can be worsened with the physical stresses of a pregnancy. Proper genetic counseling is imperative.

Prevention & Prophylaxis

It is difficult to chart preventive measures for a birth defect like hypochodroplasia because a child with this form of short stature and shortened limbs may be born to average-sized parents. If there is any hypochodroplasia within near relatives, it is advised that a parent have genetic testing to assess the risk that their child may be born with the condition. The gene for dwarfism, fibroblast growth factor receptor 3, can be identified with testing in a parent at risk of passing the mutation to children.