A New X-Linked Mental Retardation Syndrome with Diplegia and Delayed Myelination

We report three boys (4, 6 and 8 years old) in a Japanese family with X-linked (XL) recessive severe mental retardation (MR), rigidospastic diplegia, mild athetotic movement of the upper limbs, delayed myelination and poor weight gain. Neurological manifestations were non-progressive. No deterioration of development, convulsion, cerebellar signs, dysarthria, pseudobulbar signs, or minor anomalies including facial dysmorphism or macro-orchidism were found. Ocular fundus was normal. The patients' mothers and one grandmother were clinically normal. Blood chemistry was within normal limits. Serum anti-human T-cell leukemia virus-I antibody titer was negative. Levels of plasma amino acids and serum very long chain fatty acids, and lysozomal enzyme activities from leukocytes were normal. Brain magnetic resonance imaging scans showed delayed myelination. Fragile X (FRAXA), fragile XE (FRAXE), proteolipid protein and L1 cell adhesion molecule (L1CAM) genes were normal. These findings were not consistent with previously reported 13 XLMR syndromes with paralysis. We conclude that this condition is a distinct and previously undescribed XLMR syndrome.