Original articleSleep abnormalities in mentally retarded autistic subjects: Down's syndrome with mental retardation and normal subjects
Introduction
Autistic social dysfunction arises early in development and may have a broad phenotype presentation. In particular, medical literature differentiates between high functioning and low functioning subjects, depending on their social abilities and Intellectual Quotient (IQ). Moreover, even among low functioning individuals, there is evidence that certain characteristics of the cognitive patterns can differentiate them from mentally retarded subjects without autism [1], [2].
Previous research attempting to understand autistic dysfunction and behavior explored anatomic, neurochemical, genetic and neuropsychological fields suggesting the presence of a disorder in the maturation of different neuronal systems [3]. Progress has been made especially with respect to diagnosis, but many neurophysiological aspects still remain unclear.
Many authors have analyzed the importance of the relationship between REM sleep and learning or memory [4], [5], [6], [7], [8], [9]. These studies demonstrated that the integration of clinical aspects and neurophysiological characteristics can be particularly helpful in understanding the underlying cognitive deficit.
The aim of this study was to analyze sleep structure in adolescents and young adult autistic subjects with a severe mental retardation, and to compare it with that of severe MRDS and normal subjects, with particular attention to the characteristics of REM sleep, for its implication in memory and learning abilities.
Section snippets
Material and methods
We selected 10 mentally retarded autistic subjects (three F, seven M; mean age 18.2, range 12–24 years old) fulfilling the criteria of DSM-IV [10] from the Center for Mental and Motor Disabilities Anni Verdi. All subjects were affected by autism of unknown etiology. Detailed history and full physical and neurological examination were performed. The absence of associated pathology was assessed by means of karyotyping, cerebral MRI, metabolic screening, audiometry, visual acuity test and
Results
Compared to MRDS subjects, MRIA subjects showed a significantly higher amount of REM sleep percentage (P=0.008), of REM activity (P=0.004), and US percentage (P=0.0004). Although they showed a trend to lower frequency of awakening and a higher R index, they were statistically insignificant.
Compared to normal subjects, autistic subjects presented a significant reduction of REM sleep percentage (P=0.008) and a significant increase of US (P=0.0004). Their sleep continuity was disturbed by an
Sleep pattern in mentally retarded subjects
Several studies on sleep organization in mentally retarded subjects demonstrated the peculiarity of their sleep pattern [17], [18], [19], [20], [21], [22]. In fact, authors reported an increase of REM sleep latency, a reduction of REM sleep percentage and number of REM cycles, and the presence of undifferentiated sleep. The sleep characteristics described above are not specific of an etiology of mental retardation while their severity seems to be positively correlated to the severity of mental
Conclusions
Current genetic, biochemical, pathological and neurophysiological studies cannot give definite answers in autism, but the hypothesis of an early event that causes a disturbed development involving several structures and, in particular, serotoninergic and perhaps dopaminergic pathways, becomes more reasonable. It seems that, at least in severely mentally retarded autistic subjects, there is a deficit of the control of phasic elements of REM sleep with an abnormal presence of brief twitches in
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