The effects of the condition include learning difficulties, a characteristic facial appearance and mild anaemia. Affected boys have severe learning difficulties and milestones are delayed. Speech is usually not achieved.
Affected boys tend to suffer frequent colds and recurring chest infections.
Most of the boys have genital abnormalities, most frequently undescended testes. Feeding problems and regurgitation are commonly present. Sleep disturbance and mouthing may occur in some children. World-wide, over 50 affected families have been identified with this condition. The underlying gene has recently been identified.