Among hypomyelination leukodystrophies, the X-linked Allan-Herndon-Dudley syndrome (AHDS) is a psychomotor retardation characterized by severe intellectual deficiency, neuromuscular impairment and altered thyroid hormone (TH) levels in the serum (Friesema et al., 2004; Dumitrescu et al., 2004; Brockmann et al., 2005). The gene discussed is TH; the disease is leukodystrophy.