Sleep abnormalities in mentally retarded autistic subjects: Down's syndrome with mental retardation and normal subjects

We compared sleep parameters in mentally retarded infantile autism (MRIA) a nd mentally retarded Down's syndrome (MRDS) by means of polysomnography, ev aluating traditional analysis with particular attention to the phasic compo nents in each disorder. Data were compared with those obtained in normal su bjects matched for age and sex. Mental age, Intellectual Quotient and the C hildhood Autism Rating Scale were performed to obtain an estimation of the neuropsychological deficit. Abnormalities of phasic components of sleep and the presence of REM sleep components into non-REM sleep were observed in b oth MRIA and MRDS even if in different ways. In fact, MRDS subjects present ed a reduction of REM sleep percentage and R index (number of high frequenc y REMs against number of low frequency REMs) and this was positively correl ated to a low IQ. Unlike MRDS subjects, MRIA subjects did not show any para llelism between intellectual abilities and REM sleep deficit. In addition, the presence of undifferentiated sleep in autistic subjects implies a matur ational deficit that is still present in adulthood. Finally, a high R index in MRIA was observed. This finding, which is not present in MRDS, could re present an estimation of the disorganized arrival of information caused by a dyscontrol or a reduction of inhibitor pathway. With reference to sleep m echanisms, our results suggest that the cognitive deficit in MRIA may diffe r from that of MRDS subjects. A maturational deficit of CNS with a dysfunct ion of brainstem monoaminergic neurons could represent the underlying mecha nism. (C) 1999 Elsevier Science B.V. All rights reserved.