Achondroplasia is a genetic disorder whose primary feature is dwarfism. In those with the condition, the arms and legs are short, while the torso is typically of normal length. Those affected have an average adult height of 131 centimetres (4 ft 4 in) for males and 123 centimetres (4 ft) for females. Other features include an enlarged head and prominent forehead. Complications can include sleep apnea or recurrent ear infections. The disorder does not generally affect intelligence.Achondroplasia is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene that results in its protein being overactive. The disorder has an autosomal dominant mode of inheritance, meaning only one mutated copy of the gene is required for the condition to occur. About 80% of cases result from a new mutation, which originates in the father's sperm. The rest are inherited from a parent with the condition. The risk of a new mutation increases with the age of the father. In families with two affected parents, children who inherit both affected genes typically die before birth or in early infancy from breathing difficulties. The condition is generally diagnosed based on the symptoms but may be confirmed by genetic testing.Treatments may include support groups and growth hormone therapy. Efforts to treat or prevent complications such as obesity, hydrocephalus, obstructive sleep apnea, middle ear infections or spinal stenosis may be required. Life expectancy of those affected is about 10 years less than average. Achondroplasia is the most common cause of dwarfism and affects about 1 in 27,500 people. The shortest known adult with the condition is Jyoti Amge, at 62.8 centimetres (2 ft 0.7 in).