Achondroplasia is the most common form of genetically induced short stature. The characteristic features that are already visible at birth are rhizomelia, long and narrow trunk, macrocephaly with a balcony forehead, midface hypoplasia and a flat nose root.
The gross motor skills are usually slowed down due to the short extremes and existing hypotonia. Both midface hypoplasia and hypertrophy of the adenoids and tonsils can lead to obstructive sleep apnea.
Frequent respiratory tract infections and middle ear infections can cause decreased hearing and delayed speech development. Thoracolumbar kyphosis is very common in early childhood. Most joints are overstretched, the hands are wide, short and trident. Frequently, O-legs (Genu varum) occur in childhood. In addition, there is little risk of developing hydrocephalus with increased intracranial venous pressure.
Spinal canal stenosis in the lower lumbar region and associated neurological impairments are more common in adulthood, as are cardiovascular diseases. Obesity also often occurs. Adults reach a body height of about 131 cm (men) or 124 cm (women).
Achondroplasia is based on mutations in the gene FGFR3, which lies on chromosome 4. The defect is inherited autosomal dominant. FGFR3 is a receptor tyrosine kinase that binds fibroblast growth factors and then triggers various signaling cascades. This results in an inhibition of cartilage proliferation and the stunting of endochondral ossification. There is a premature occlusion of the epiphyseal plates. About 80% of the cases are caused by new mutations. Compared to the normal population there is a slightly reduced life expectancy due to possible cardiovascular diseases.