MCT8
What Is MCT8?
MCT8-specific thyroid hormone cell transporter deficiency (MCT8 deficiency) is a genetic disorder characterized by severe intellectual disability, an impaired ability to speak, low muscle tone (hypotonia), disorganized movements and specific thyroid test abnormalities.
Except for poor muscle tone, most affected infants appear to develop normally during the first months of life. However, by about two months of age, an affected infant may seem weak and be unable to hold up their head. Due to hypotonia, severely reduced motor development and other abnormalities, affected children very rarely develop the ability to walk and when they do, it is with a shuffling gait. Associated features often include underdevelopment (hypoplasia) and decreasing (atrophy) of muscle tissue; weakness and stiffness of the legs (spastic paraplegia) with exaggerated reflexes (hyperreflexia) and relatively slow, involuntary, purposeless (dyskinetic) movements. Writhing movements (athetoid movements) and/or other movement abnormalities are less common. Affected individuals may also have characteristic features of the skull and face. MCT8 deficiency is an X-linked genetic disorder.
MCT8 deficiency is a rare inherited disorder that affects mostly males. More than 300 families have been identified with 210 different MCT8 gene variants. The frequency of MCT8 deficiency among people with intellectual disability is not known, though estimated to occur in 1 in 70,000 newborns.
Signs & Symptoms:
MCT8 deficiency is primarily characterized by severe intellectual disability, hypotonia and movement abnormalities. Associated findings may include underdevelopment (hypoplasia) and decreasing (atrophy) of various skeletal (voluntary) muscles; an impaired ability to coordinate certain voluntary movements (ataxia); weakness and stiffness of the legs (spastic paraplegia) with associated hyperreflexia and involuntary, rapid, repeated involuntary contractions and relaxations of the legs (clonus). Movement abnormalities are common and include dyskinetic attacks or relatively slow, writhing movements (athetoid movements) and/or other movement abnormalities.