Elsevier

Brain and Development

Volume 21, Issue 8, 1 December 1999, Pages 548-553
Brain and Development

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

https://doi.org/10.1016/S0387-7604(99)00077-7Get rights and content

Abstract

We compared sleep parameters in mentally retarded infantile autism (MRIA) and mentally retarded Down's syndrome (MRDS) by means of polysomnography, evaluating traditional analysis with particular attention to the phasic components in each disorder. Data were compared with those obtained in normal subjects matched for age and sex. Mental age, Intellectual Quotient and the Childhood 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 both MRIA and MRDS even if in different ways. In fact, MRDS subjects presented a reduction of REM sleep percentage and R index (number of high frequency REMs against number of low frequency REMs) and this was positively correlated to a low IQ. Unlike MRDS subjects, MRIA subjects did not show any parallelism between intellectual abilities and REM sleep deficit. In addition, the presence of undifferentiated sleep in autistic subjects implies a maturational 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 represent an estimation of the disorganized arrival of information caused by a dyscontrol or a reduction of inhibitor pathway. With reference to sleep mechanisms, our results suggest that the cognitive deficit in MRIA may differ from that of MRDS subjects. A maturational deficit of CNS with a dysfunction of brainstem monoaminergic neurons could represent the underlying mechanism.

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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