What is the Cause of Achondroplasia?

Achondroplasia Overview: Genetic Mutation, Symptoms & Care

Achondroplasia is a genetic condition that affects bone development, leading to dwarfism caused by mutations that impact the growth of the arms and legs. Individuals with achondroplasia usually have a normal-sized torso with shorter arms and legs, resulting in disproportionate dwarfism. 

Most children diagnosed with achondroplasia go on to live full, healthy lives. Therefore, it is crucial to understand the cause and symptoms of this condition for early diagnosis and timely treatment. Keep reading to learn about the cause of achondroplasia and for more details. 

What Causes Achondroplasia? 

During the initial phases of foetal growth, most of the skeleton consists of cartilage. Typically, this cartilage gradually transforms into bone as development progresses. In individuals with achondroplasia, much of this cartilage fails to convert into bone properly. This occurs due to mutations in the FGFR3 (fibroblast growth factor receptor 3) gene. 

The FGFR3 gene provides instructions for producing a protein that plays a key role in bone growth and maintenance. When mutations affect this gene, the resulting protein becomes overly active, disrupting normal bone formation and leading to the skeletal abnormalities seen in achondroplasia. 

What are the Symptoms of Achondroplasia? 

The symptoms of achondroplasia can appear in infancy and continue to develop over time. Common signs include: 

• There is a noticeably large head compared to the body, with shorter arms and legs, particularly the upper arms and thighs. 
• A prominent forehead (frontal bossing) along with a flattened bridge of the nose. 
• A smaller or underdeveloped midface can make the lower jaw appear more prominent. 
• Flattened cheekbones may lead to dental crowding. 
• Fingers may appear short, with the middle and ring fingers spreading apart, giving the hands a trident-like appearance. 
• The elbows and hips may also have a restricted range of motion, making it difficult to fully straighten or rotate them. 
• Limited ability to fully extend or rotate the elbows and extend the hips. 
• Reduced muscle tone (hypotonia) 
• A noticeable rounding or hump may develop in the middle to lower part of the back, often called a gibbus deformity. 

As children grow, additional symptoms may include: 

• Height that is considerably below the normal range for an individual’s age and gender. 
• Delays in achieving developmental milestones. 
• Bowed legs (genu varum) 
• Abnormal curvatures of the spine, such as kyphosis (outward curve) and lordosis (inward curve) 
• Delayed independent walking often begins between 2 and 3 years of age. 
• Intelligence is usually normal, but hydrocephalus or spinal compression may cause transient developmental delays. 
• Temporary speech difficulties due to tongue thrust, midface hypoplasia, or recurrent ear infections due to Eustachian tube dysfunction, which generally resolve by school age. 
• A higher likelihood of developing obesity. 
• Some individuals may experience breathing difficulties. 
• A reduced width of the spinal canal, known as spinal stenosis, can compress the spinal nerves. 

How is Achondroplasia Diagnosed? 

Doctors can diagnose achondroplasia either during pregnancy or after the baby is born. Listed below are the times when a diagnosis is performed: 

1. Diagnosis During Pregnancy : Certain signs of achondroplasia may be visible on an ultrasound, such as hydrocephalus, which is an unusually large head. If achondroplasia is suspected, your doctor may recommend genetic testing. This involves analysing a sample of amniotic fluid, which surrounds the baby in the womb, to check for mutations in the FGFR3 gene. 
2. Diagnosis After Birth : After birth, doctors often identify achondroplasia based on the baby’s physical characteristics. To help confirm the diagnosis, they may order X-rays to measure bone length. Blood tests may also be done to detect mutations in the FGFR3 gene. 

Is Achondroplasia Hereditary? 

Achondroplasia is a genetic condition inherited in an autosomal dominant manner; however, most cases (about 80%) result from a new (de novo) mutation in the FGFR3 gene in children born to parents of average height. It is rare for these parents to have another child affected by the condition. 

Achondroplasia is inherited in an autosomal dominant manner, which means that only one parent needs to have and transmit the gene for their child to develop the condition. If one parent has achondroplasia while the other does not, there is a 50% probability that their child will inherit the gene and develop the disorder. 

If both parents are affected by achondroplasia, there is a 25% likelihood that the child will inherit two copies of the faulty gene (homozygous achondroplasia), which often results in stillbirth or death soon after birth. 

Reader information: This article is intended for general informational and educational purposes only. It does not constitute medical advice, diagnosis, or treatment. Achondroplasia and its associated health concerns can vary between individuals. Readers should consult a qualified healthcare professional or genetic specialist for personalized medical guidance, diagnosis, and management. Information provided here should not be used as a substitute for professional medical consultation or care. 

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