Abstract
<jats:title>Abstract</jats:title> <jats:p>This chapter provides pictures and clinical details of Allan-Herndon-Dudley syndrome, an XLID with generalized muscle hypoplasia, childhood hypotonia, ataxia, athetosis, dysarthria, and spastic paraplegia. The gene (SLC16A2) is responsible for transporting triiodothyronine into neurons. Marked hypotonia and paucity of skeletal muscle mass permit diagnosis in infancy. Although the facies do not appear distinctive in childhood, there is a tendency in adult life toward elongation of the face, cupping or abnormal folding of the ears, and large ears. Spastic paraplegia and contractures of the small and large joints become evident in adult life. Shallow pectus excavatum, ulnar deviation of the hand, scoliosis, and valgus position of the great toe may be seen. Excessive drooling and dysarthria continue into adult life, deep tendon reflexes become hyperactive, and clonus and Babinski signs may be seen. Fungal infections appear common.</jats:p>