X-linked intellectual disability, Turner type is characterised by moderate to severe intellectual deficit in boys and moderate intellectual deficit in girls. It has been described in 14 members from four generations of one family. Macrocephaly was reported and holoprosencephaly may also be present (two family members). The mode of transmission is X-linked semi-dominant.

Occipitofrontal (head) circumference greater than 97th centile compared to appropriate, age matched, sex-matched normal standards. Alternatively, a apparently increased size of the cranium.