Achondroplasia: symptoms, causes, diagnosis and treatment

Definition

Achondroplasia is a bone growth disorder that causes disproportionate dwarfism. Dwarfism is defined as a condition of short stature as an adult. People with achondroplasia are short in stature with a normal sized torso and short limbs. It’s the most common type of disproportionate dwarfism.

History

Achondroplasia was discovered by Dr. John Wasmuth and his team of scientist in 1994 but he only published the cause of achondroplasia which mainly stated that achondroplasia is caused by the fibroblast growth factor receptor 3 gene which is part of chromosome 4.

A French scientist named Pierre Maroteaux has done research on dwarfism and was the first to mention dwarfism. A  French physician named Maurice Lamy and her team studied the order and the number of chromosomes of patients who are dwarfs

Epidemiology

Achondroplasia is listed as a “rare disease” by the Office of Rare Diseases (ORD) of the National Institutes of Health (NIH). This means that Achondroplasia, or a subtype of Achondroplasia, affects less than 200,000 people in the US population.

Ophanet, who are a consortium of European partners, currently defines a condition rare when if affects 1 person per 2,000. They list Achondroplasia as a “rare disease”. More information about Achondroplasia is available from Orphanet

Types

Given below are few common types of achondroplasia:

Pseudo-Achondroplasia: Although the appearance of face is normal, the child may develop irregular growth plates in the knees and hips.

Hypochondroplasia: Hypochondroplasia is a condition which affects the child less severely. The height of the child is over 54 inches excluding spinal stenosis.

Risk factors

Some of the risk factors for Achondroplasia Dwarfism are:

  • A child who has a parent or parents with Achondroplasia Dwarfism
  • Children with parents that have a mutated FGFR3 gene
  • Advanced paternal age causing mutations

Causes

Gene causes achondroplasia

Achondroplasia is caused by mutations in the FGFR3 gene which codes for a protein (fibroblast growth factor receptor 3) that is important for the maintenance of bone and brain tissues. Two specific mutations in this gene are responsible for almost all cases of achondroplasia. These mutations limit the process of ossification, or the formation of bone from cartilage. The FGFR3 gene is located on the short (p) arm of chromosome 4 in chromosome band 4p16.3.

Symptoms

The typical appearance of achondroplastic dwarfism can be seen at birth. Symptoms may include:

  • Abnormal hand appearance with persistent space between the long and ring fingers
  • Bowed legs
  • Decreased muscle tone
  • Disproportionately large head-to-body size difference
  • Prominent forehead (frontal bossing)
  • Shortened arms and legs (especially the upper arm and thigh)
  • Short stature (significantly below the average height for a person of the same age and sex)
  • Spinal stenosis
  • Spine curvatures called kyphosis and lordosis

Diagnosis and tests

Diagnosis during pregnancy

Some characteristics of achondroplasia are detectable during an ultrasound. These include hydrocephalus, or an abnormally large head. If your doctor suspects achondroplasia, genetic tests may be ordered. These tests look for the defective FGFR3 gene in a sample of amniotic fluid, which is the fluid that surrounds the fetus in the womb.

Diagnosis after your child is born

Your doctor can diagnose your child by looking at his or her features. The doctor may also order X-rays to measure the length of your infant’s bones. This can help confirm a diagnosis. Blood tests may also be ordered to look for the defective FGFR3 gene.

Treatment and medications

There’s no cure or specific treatment for achondroplasia. If any complications arise, then your doctor will address those issues. For instance, antibiotics are given for ear infections and surgery may be performed in severe cases of spinal stenosis.

Some doctors use growth hormones to increase the growth rate of a child’s bones. However, their long-term effects on height haven’t been determined and are thought to be modest at best.

Prevention:

Genetic counseling may be helpful for prospective parents when one or both have achondroplasia. However, because achondroplasia most often develops spontaneously, prevention is not always possible.

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