Achondroplasia

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Achondroplasia is the most common form of short-limbed dwarfism. The word achondroplasia means "without cartilage formation." Cartilage is a tough but flexible tissue that makes up much of the skeleton during early development. However, in people with achondroplasia the problem is not forming cartilage but converting it to bone (a process called ossification), particularly in the long bones of the arms and legs. Achondroplasia is similar to another skeletal disorder called hypochondroplasia, but the features of achondroplasia tend to be more severe.

All people with achondroplasia have short stature. Without treatment, the average height of an adult male with achondroplasia is 131 centimeters (4 feet, 4 inches), and the average height for adult females is 124 centimeters (4 feet, 1 inch). Characteristic features of achondroplasia include an average-size trunk, short arms and legs with particularly short upper arms and thighs, limited range of motion at the elbows, and an enlarged head (macrocephaly) with a prominent forehead. Fingers are typically short and the ring finger and middle finger may diverge, giving the hand a three-pronged (trident) appearance.

Health problems commonly associated with achondroplasia include obesity and recurrent ear infections. People with achondroplasia are generally of normal intelligence. In childhood, individuals with the condition usually develop a pronounced and permanent sway of the lower back (lordosis) and bowed legs. Some affected people also develop abnormal front-to-back curvature of the spine (kyphosis) and back pain.

As affected individuals age, they may experience a potentially serious complication of achondroplasia called spinal stenosis. Spinal stenosis is a narrowing of the spinal canal that can pinch (compress) the upper part of the spinal cord. Spinal stenosis causes with pain, tingling, and weakness in the legs that can make walking difficult. An uncommon but serious complication of achondroplasia in early childhood is stenosis of the hole at the base of the skull where the spinal cord comes out of brain (foramen magnum). This complication can cause compression of the brain stem, which can lead to pauses in breathing during sleep (sleep apnea) or a condition known as hydrocephalus. Hydrocephalus is a buildup of fluid in the brain that can lead to increased head size and related brain abnormalities.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Variants (also called mutations) in the FGFR3 gene cause achondroplasia. The FGFR3 gene provides instructions for making a protein that is involved in the development and maintenance of bone and brain tissue. Two specific variants in the FGFR3 gene are responsible for almost all cases of achondroplasia. These variants cause the FGFR3 protein to be overly active, which interferes with skeletal development and leads to the disturbances in bone growth seen with this disorder.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

Achondroplasia is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. About 80 percent of people with achondroplasia are born to parents who do not have the condition and are of average heights; these cases are caused by new variants in the FGFR3 gene. In the remaining cases, people with achondroplasia inherit an altered FGFR3 gene from one or two affected parents.

Individuals who inherit two altered copies of the FGFR3 gene typically have a severe form of achondroplasia that causes extreme shortening of the bones and an underdeveloped rib cage. These individuals are usually stillborn or die shortly after birth from respiratory failure.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Achondroplasia is the most common type of short-limbed dwarfism. The condition occurs in 1 in 15,000 to 40,000 newborns.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Bowing of the legs · Very frequent (99-80%)

A bending or abnormal curvature affecting a long bone of the leg.

Disproportionate short stature · Very frequent (99-80%)

A kind of short stature in which different regions of the body are shortened to differing extents.

Kyphosis · Very frequent (99-80%)

Exaggerated anterior convexity of the thoracic vertebral column.

Limb undergrowth · Very frequent (99-80%)

Limb shortening because of underdevelopment of one or more bones of the extremities.

Thoracolumbar kyphosis · Very frequent (99-80%)

Hyperconvexity of the thoracolumbar spine producing a rounded or humped appearance.

Abnormal midface morphology · Frequent (79-30%)

An anomaly of the midface, which is a region and not an anatomical term. It extends, superiorly, from the inferior orbital margin to, inferiorly, the level of nasal base. It is formed by the maxilla (upper jaw) and zygoma and cheeks and malar region. Traditionally, the nose and premaxilla are not included in the midface.

Anteverted nares · Frequent (79-30%)

Anteriorly-facing nostrils viewed with the head in the Frankfurt horizontal and the eyes of the observer level with the eyes of the subject. This gives the appearance of an upturned nose (upturned nasal tip).

Brachydactyly · Frequent (79-30%)

Digits that appear disproportionately short compared to the hand/foot. The word brachydactyly is used here to describe a series distinct patterns of shortened digits (brachydactyly types A-E). This is the sense used here.

Other findings in the same source

From: Orphanet

Additional reported features include Central sleep apnea (Frequent (79-30%)); Cervical spinal canal stenosis (Frequent (79-30%)); Depressed nasal bridge (Frequent (79-30%)); Floppy infant (Frequent (79-30%)); Frontal bossing (Frequent (79-30%)); Functional abnormality of the middle ear (Frequent (79-30%)); Hearing impairment (Frequent (79-30%)); Knee joint hypermobility (Frequent (79-30%)); Limited elbow extension (Frequent (79-30%)); Lumbar hyperlordosis (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Achondroplasia is Orthopaedics, with a orthopaedic specialist as the relevant type of clinician. General physician / Family Medicine; paediatrician for children. Referral depends on symptoms.

Additional services that may be relevant, depending on the findings, include: Clinical Genetics.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• What explains the change in pain, movement or function?
• Which activities need adjustment while the diagnosis is being clarified?
• What are the roles of rehabilitation, observation and surgery in this situation?

Treatment discussions and follow-up

Where the source describes treatments, these are an overview of possible care, not a prescription for an individual. Ask which option applies to the confirmed diagnosis, what benefit is expected, what adverse effects to watch for and how progress will be assessed. Availability, approvals and local practice can differ from the country described in the source.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.