We applied a public health approach to the study of mental retardation by providing a basic descriptive epidemiological analysis using a large statewide linked birth and public school record database (N = 327,831). Sociodemographic factors played a key role across all levels of mental retardation. Birthweight less than 1000 g was associated with…

Behavioral phenotypes of individuals with Williams syndrome and individuals with Down syndrome have been contrasted in relation to short-term memory. People with Down syndrome are stronger visuospatially and those with Williams syndrome are stronger verbally. We examined short-term memory, then explored whether dual-task processing further…

This review examines clinical aspects of seizures among individuals with Down's syndrome and explores possible mechanisms by which the trisomy 21 brain may generate seizures. Evidence suggests an interplay between pathologically hyperexcitable membrane properties, altered neuronal structure, and abnormal inhibitory neurotransmission. (Author/JDD)

This commentary critiques two papers by Curt Sandman, pointing out interpretive problems in models explaining self-injurious behavior in terms of opioids. Withdrawal effects are emphasized as an alternative to hypotheses asserting congenital opioid excess as a cause of sensory depression or an addiction to a relative excess of opioid activity in…

This paper answers criticism (EC 601 030) of the authors' work regarding opioid explanations of self-injurious behavior. Possible withdrawal effects are ruled out as an explanation, in favor of opioid excess leading to sensory depression and addiction to relative excesses of opioid activity in the brain. Alternative models of consequences of…

This paper reviews hypotheses suggesting psychological, behavioral, physiological, or neurochemical factors as causes of self-injury in individuals with severe/profound mental retardation. A compulsive behavior hypothesis is introduced, suggesting that self-injury occurs with cerebral dysfunction is compulsive, may occur in the context of a…

Sensitivity theory divides the causes of challenging behavior into three categories, aberrant contingencies, aberrant environments, and aberrant motivation. This paper replies to criticism that sensitivity theory is circular and unsupported by empirical evidence by reporting on studies that support the theory and rejecting the idea that…

This study examined whether the variability in development in fragile X syndrome is related to FMR protein deficiency in 53 young males with various degrees of the syndrome. FMR protein expression accounted for a small but significant amount of variance in level, but not rate, of development. Findings support the hypothesized relationship but…

The etiology of intellectual disability was studied both in incident (n = 9,432) and prevalent (n = 9,351) populations in a one-year birth cohort born in Northern Finland in 1985-1986. Data from multiple sources were used to follow the children until the age of 11.5 years. Of the incident cases (n = 119) with intellectual disabilities, 66.4% had…

This paper describes current neurological knowledge regarding the recognition, diagnosis, and classification of frontal lobe seizures, and then critiques a study by A. Gedye which suggested that self-injury may be involuntary and related to frontal lobe seizure activity. (JDD)

Comparison of the production of repetitive speech during conversations in 30 people with either fragile X syndrome, autistic disorder, or mental retardation not caused by fragile X found repetitive speech more prevalent among those with fragile X. Results support the hypothesis that such speech dysfluency reflects the effects of physiological…

A prospective assessment following a step-wise protocol in 281 patients with unexplained cognitive delay was used to assess diagnostic possibilities. Diagnostic procedures were complex and required a multidisciplinary approach. One third of diagnoses was established based on clinical history and physical exam only; for another third, clinical…

Mortality of people with mental retardation (n=118,653) in California was examined. Up to about age 35, mortality rates of people with Down syndrome (DS) were comparable to those of people with mental retardation due to other causes. Subsequently, mortality for the DS group doubled every 6.4 years compared with 9.6 years for people without DS.…

This study examined structural characteristics and environmental variables in the stereotypic behaviors of eight individuals with developmental disabilities. Findings indicated that structural characteristics (percentage of time, bout length, and bout length variability) were highly correlated. Also, stereotyped behaviors were more likely to occur…

This nontechnical review of the literature on Rett Syndrome, a developmental disability found only in females, examines the syndrome's history, diagnostic criteria, clinical stages, incidence, differential diagnosis, etiology, genetics, treatment approaches, and prognosis. (Author/DB)