Why does it occur
The FGFR3 gene encodes a receptor that inhibits the division of cartilage cells in growth zones. When the gene changes, the receptor becomes overactive, and cartilage growth is inhibited more than necessary. Inheritance is dominant: if one parent has achondroplasia, the chance of passing it on to a child is one in two. However, the vast majority of children are born to parents of normal height, because the change first occurs in the reproductive cell, usually the father's, and the likelihood of this increases somewhat with the age of the father. Lifestyle, nutrition and parental behavior do not affect this in any way.
- Change in the FGFR3 gene with excessive receptor activity
- Autosomal dominant inheritance
- Most cases are a new mutation
- Relationship with father's age
- Does not depend on nutrition and lifestyle
- The risk of transmission to a child from an affected parent is one in two.
How it manifests itself
Features are noticeable already at birth, and sometimes on an ultrasound in the third trimester: the limbs are shorter than expected, the head is large. The shortening is more pronounced in the shoulder and thigh than in the forearm and lower leg. The fingers are arranged in a characteristic way, with a discrepancy between the middle and ring fingers. Due to their structural features, children begin to sit and walk later than their peers, and this is not a sign of developmental delay. A pronounced lumbar deflection, curvature of the legs, and limited extension at the elbows are often observed. Intelligence is normal, and children learn on par with their peers.
- Short limbs with a normal body length
- Large head, protruding forehead, depressed bridge of the nose
- Characteristic divergence of the fingers
- Later development of sitting and walking
- Pronounced arch in the lower back
- Curvature of the shins
- Limitation of elbow joint extension
- Normal intelligence
Complications being monitored
The main concern of the first year of life is the narrowing of the foramen magnum, through which the transition of the spinal cord into the trunk passes. Compression is manifested by pauses in breathing during sleep, lethargy, severe muscle weakness, and requires consultation with a neurosurgeon. Often there are breathing disorders during sleep due to narrow upper respiratory tracts, recurring otitis media with hearing loss, which is important for speech development. In adolescents and adults, the main problem is a narrowing of the spinal canal in the lumbar region with pain in the legs when walking, numbness and weakness.
- Narrowing of the foramen magnum in infants
- Breathing pauses during sleep
- Recurrent otitis media and hearing loss
- Hydrocephalus
- Lumbar stenosis with pain and weakness in the legs
- Curvature of the legs requiring orthopedic correction
- Excess weight, which increases stress on the joints and spine
Diagnosis and observation
The diagnosis is usually made by clinical signs and a characteristic x-ray picture: shortened bones, narrow sacral notch, narrowing of the distance between the roots of the lumbar vertebral arches. Genetic testing confirms a change in the FGFR3 gene and is useful in doubtful cases and for family planning. The observation is based on special growth curves for children with achondroplasia: conventional centile tables are not suitable here. Head circumference, neurological status, hearing, breathing during sleep are regularly assessed, and tomography of the cervical spine is performed if indicated.
- X-ray of the skeleton and spine
- CT or MRI of the craniovertebral junction
- Genetic study of the FGFR3 gene
- Special growth curves for achondroplasia
- Monitoring head circumference in infants
- Audiometry and examination by an otolaryngologist
- Sleep breathing study for snoring and apnea
- Examination by a neurologist and orthopedist over time
Treatment and help
There is no therapy that completely eliminates the cause, but modern approaches make it possible to influence growth rates, and the question of such treatment is decided by a specialist individually. The main attention is paid to the prevention and treatment of complications: neurosurgical intervention for spinal cord compression, treatment of otitis media, breathing support during sleep, orthopedic correction of curvature of the legs. Limb lengthening is possible, but it is a series of lengthy operations with risks, and the decision is made carefully, preferably at an age when a teenager is participating in the discussion. Adaptation of everyday life and support of the child’s self-esteem are very important.
- Supervision of a multidisciplinary team of specialists
- Neurosurgical intervention for spinal cord compression
- Treatment of otitis media and hearing control
- Correction of breathing disorders during sleep
- Orthopedic treatment of curvature of the legs
- Discussion of limb lengthening with a teenager
- Weight control and feasible physical activity
- Adaptation of life and school environment, psychological support