Mutational spectrum of <i>NSDHL</i> in CHILD syndrome

CHILD syndrome (congenital hemidysplasia with ichthyosiform nevus and limb defects, MIM 308050) is an X linked dominant, male lethal, multisystem birth defect characterised by an inflammatory epidermal nevus showing a unique lateralisation pattern and strict midline demarcation. Hypoplasia or aplasia of skeletal or visceral structures may be found ipsilateral to the major cutaneous involvement.1 Owing to the highly characteristic clinical and histopathological features of the CHILD naevus,2 a diagnosis can be established not only in classical cases (fig 1) but also in cases with minimal or atypical involvement.3 In 2000, mutations in NSDHL (NAD(P)H steroid dehydrogenase-like protein) at Xq28 were identified by some of us to be the cause of this syndrome.4 Four additional NSDHL mutations have subsequently been reported in individuals with CHILD syndrome.5–8 Studies carried out on the murine Nsdhl mutants bare patches (Bpa) and striated (Str) have shown that this gene encodes a 3β-hydroxysteroid dehydrogenase (3β-HSD) that catalyses a step in the post-squalene cholesterol biosynthetic pathway and is localised within membranes of the endoplasmic reticulum and on the surface of intracellular lipid storage droplets.9–11 Non-functional NSDHL might cause the CHILD phenotype through a lack of cholesterol or other sterols downstream of the block in biosynthesis, or by the accumulation of intermediates upstream of the product generated by NSDHL. Figure 1  Thirteen year old patient with CHILD syndrome (case 9, table 1): ichthyosiform nevus showing lateralisation with unilateral distribution and midline demarcation; ipsilateral hypoplasia of arm and hand. Reproduced with permission. A related trait, X linked dominant chondrodysplasia punctata (CDPX2, MIM 302960),22 is caused by mutations in EBP (emopamil binding protein) at Xp11.22–p11.23 that functions similarly in the late cholesterol biosynthesis, downstream of NSDHL .23,24 In the past, a case of X linked dominant chondrodysplasia punctata showing unilateral involvement …