NSDHL-related disorders include CHILD (congenital hemidysplasia with ichthyosiform nevus and limb defects) syndrome, an X-linked disorder that is usually male lethal during gestation and thus predominantly affects females; and CK syndrome, an X-linked disorder that affects males. CHILD syndrome is characterized by unilateral distribution of ichthyosiform skin lesions and ipsilateral limb defects that range from shortening of the metacarpals and phalanges to absence of the entire limb. Intellect is usually normal. The ichthyosiform skin lesions are usually present at birth or in the first weeks of life; new lesions can develop in later life. Onychodystrophy and periungual hyperkeratosis are common. Heart, lung, and kidney malformations can also occur. CK syndrome is characterized by mild-to-severe cognitive impairment and behavior problems (aggression, attention-deficit/hyperactivity disorder [ADHD], and irritability). All reported affected males have developed seizures in infancy and have cerebral cortical malformations and microcephaly. All have distinctive facial features, a thin habitus, and relatively long, thin fingers and toes. Some have scoliosis and kyphosis. Strabismus is common. Optic atrophy is also reported.