A congenital disorder of bone formation with clavicular hypoplasia or agenesis with a narrow thorax, allowing approximation the shoulders in front of the chest occurring with delayed ossification of the skull, excessively large fontanelles, and delayed closing of the sutures. The fontanelles may remain open until adulthood, but the sutures often close with interposition of wormian bones. Bosses of the frontal, parietal, and occipital regions give the skull a large globular shape with small face. The characteristic skull abnormalities are sometimes referred to as the "Arnold head" named after the descendants of a Chinese who settled in South Africa and changed his name to Arnold. More than 100 additional anomalies may be associated, including wide pubic symphysis, dental abnormalities, short middle phalanges of the fifth fingers, delayed skeletal maturation, hearing deficiency, and mild mental retardation in some cases.