An aetiological study of 1,000 patients with an I.Q. assessment below 51

Diagnostic investigations in individuals with mental retardation: a systematic literature review of their usefulness

There are no guidelines available for diagnostic studies in patients with mental retardation (MR) established in an evidence-based manner. Here we report such study, based on information from original studies on the results with respect to detected significant anomalies (yield) of six major diagnostic investigations, and evaluate whether the yield differs depending on setting, MR severity, and gender. Results for cytogenetic studies showed the mean yield of chromosome aberrations in classical cytogenetics to be 9.5% (variation: 5.4% in school populations to 13.3% in institute populations; 4.1% in borderline-mild MR to 13.3% in moderate-profound MR; more frequent structural anomalies in females). The median yield of subtelomeric studies was 4.4% (also showing female predominance). For fragile X screening, yields were 5.4% (cytogenetic studies) and 2.0% (molecular studies) (higher yield in moderate-profound MR; checklist use useful). In metabolic investigations, the mean yield of all studies was 1.0% (results depending on neonatal screening programmes; in individual populations higher yield for specific metabolic disorders). Studies on neurological examination all showed a high yield (mean 42.9%; irrespective of setting, degree of MR, and gender). The yield of neuroimaging studies for abnormalities was 30.0% (higher yield if performed on an indicated basis) and the yield for finding a diagnosis based on neuroradiological studies only was 1.3% (no data available on value of negative findings). A very high yield was found for dysmorphologic examination (variation 39-81%). The data from this review allow conclusions for most types of diagnostic investigations in MR patients. Recommendations for further studies are provided.

Genetic syndromes among individuals with mental retardation

Individuals with mental retardation more commonly have malformations and other structural anomalies than individuals without mental retardation. In many cases, the associated anomalies comprise recognizable syndromes caused by genetic or environmental insults. To co-occurrence of structural anomalies with mental retardation thus assists in the diagnostic evaluation, particularly in infants and young children. The coexistence of structural and mental abnormalities also suggests that both originated in the embryonic period of development.

Extracellular proteases and their inhibitors in genetic diseases of the central nervous system

Cumulative evidence has shown that a delicate balance between serine proteases and their inhibitors is crucial for normal functioning of several biological pathways. The importance of proteases and their inhibitors is well documented in several human diseases. Among them, the best documented are hemophilia B, a genetic deficiency of the serine protease coagulation factor IX and serpinophathies. Alpha-1-antitrypsin deficiency (MIM 107400), is associated with early-onset emphysema and liver disease, while hereditary angioedema (HANE; MIM 106100) is caused by mutations in the C1 inhibitor, a serpin involved in the regulation of the complement cascade. Recently, two human genetic diseases of the central nervous system have been related to mutations in components of extracellular proteolytic systems. Here, we review the recent advances in this field.

Schizophrenia in people with intellectual disability: the role of pregnancy and birth complications

The literature suggests that mental illness is more common in people with intellectual disability than in the general population. Having reviewed the literature, Turner (1989) [Psychological Medicine 19, 301-14] suggested that about 3% of people with intellectual disability also have schizophrenia. As pregnancy and birth complications (PBCs) occur more commonly in people with intellectual disability than in the general population and are also implicated in the aetiology of schizophrenia, it is possible that these conditions share a common aetiology. This study reports on the occurrence of PBCs in those people with intellectual disability who develop schizophrenia. Fifty people with intellectual disability and schizophrenia were matched for age, sex, degree of intellectual disability and presence of epilepsy with a control group who did not suffer from schizophrenia or a schizophreniform psychosis. The obstetric history was obtained and events rated on a scale specifically designed for this study. This PBCs scale consists of six sub-scales covering areas of general maternal health, pregnancy, delivery, medication in labour, total medication score and neonatal score, as well as an overall total score. The study found that people with intellectual disability who develop schizophrenia have significantly higher rates of PBCs than controls. All of the sub-scales on the PBCs scale were significantly higher in people with schizophrenia, with the exception of the medication scales. Only five out of the 50 people with schizophrenia had not had a major obstetric complication, compared to 13 subjects from the control group. A number of abnormalities were specifically higher in people who later developed schizophrenia. These included: abnormally long or short labour; maternal episiotomy; maternal preeclamptic toxaemia; induction of labour; dysmaturity; maternal smoking in pregnancy; and a delay in neonatal crying. The results suggest that PBCs are important in the aetiology of schizophrenia in people with intellectual disability.

Etiologic and pathogenetic study of mental retardation with multiple congenital anomalies

Etiology and pathogenesis of MCA/MR in 1,023 patients (618 male; 405 female) with mental retardation were studied. Of 1,023 patients, there were 563 cases (317 male; 246 female) with MCA (55%). Among the MCA patients, there were 303 (156 male; 147 female) whose primary etiology was clarified (53.8%). Among the 260 patients with MCA/MR of unknown etiology, there were 23 with recognizable syndromes of unknown etiology and 7 previously reported by us as possibly having a new malformation syndrome. We had 569 patients with mental retardation of unknown etiology including 263 (41.5%) who were involved with MCA.

The aetiology of intellectual disability in Western Australia: a community-based study

A register of intellectual disability is being established to assess the level and aetiology of intellectual disability in all children born and/or living in Western Australia. 1602 children aged between six and 16 years were identified who had IQs less than 70. 40 per cent had a definite genetic basis, 20 per cent an environmental cause and 40 per cent were of unknown aetiology. The insult was prenatal in 61 per cent, 10 per cent had a possible perinatal cause, 8 per cent were postnatal and for 21 per cent the timing could not be assessed. Approximately 20 per cent had concomitant cerebral palsy and 13 per cent were epileptic. A disparity was found between rural and urban areas, the prevalence being 9.9 and 6.5 per 1000 live births.

Genetic causes of mental handicap and opportunities for prevention

Prior to 1970 nearly one half of severe mental handicap (IQ less than 50) was unexplained and genetic causes were recognized in one third of all patients. In recent years the genetic contribution has risen to 50%, with the decline in importance of environmental causes and the growing recognition of X-linked forms of mental retardation and chromosomal microdeletion syndromes. Recognition of genetic conditions is vital for accurate assessment of recurrence risks and in order, in some instances, to provide specific prenatal diagnosis. With full utilization of existing prenatal screening procedures and a more detailed family history, severe mental handicap due to genetic conditions should be reduced by 30-40%.

Causal origins of major mental handicap in the Canadian Maritime provinces

From a retrospective epidemiological survey, the prevalence of major mental handicap among seven- to 10-year-old children in the Maritime region of Canada in 1980 was estimated to be 36.5 per 10,000 children. Based on information obtained for 221 of the 307 children ascertained by the survey, prenatal origins dominated (58 per cent), followed by perinatal (10 per cent) and postnatal (4 per cent). No specific cause could be determined for 27 per cent of the children, but 41 per cent of this group had epilepsy and/or cerebral palsy in addition to major mental handicap. Significant differences were found in the causal spectrum between the Maritime region of Canada and regions studied in other developed countries. The results of this survey have implications for planning prevention programs, and for epidemiological surveillance and monitoring of adverse reproductive outcomes.

Clinical assessment of 4500 developmentally delayed individuals

Data collected on 4500 developmentally delayed clients and classified according to a modification of Heber's criteria are presented. Statistically significant associations between variables are described. Although such associations are not necessarily biologically meaningful on this evidence alone, they are presented for comparison with other data collections and to suggest areas of further investigation. An examination is made of data relating to mental retardation of unknown cause compared with mental retardation of known causes. The unknown group most resembles those with metabolic disease and least resembles those with chromosome aneuploidy. The data also suggest that mental retardation secondary to brain injury is uncommonly associated with evidence of genetic predisposition.

A study of institutionalized mentally retarded patients in Manitoba. I: Classification and preventability

This preliminary report concerns the types, and the possibility of prevention, of mental retardation found among 406 patients less than 20 years of age and with IQs less than or equal to 50 who had been admitted to institutions for the retarded in Manitoba prior to 1977. The retardation appeared to be of genetic origin in 27.8 per cent of cases, and acquired in a further 30.3 per cent. 31 per cent of the genetic and 55 per cent of the acquired, or 25.4 per cent of the total group, are considered to have been avoidable, given the full application of current techniques and knowledge.

The ophthalmological assessment of the severely retarded child

This paper details the technique for ocular assessment of the severely retarded child including the use of electrophysiological methods of examination and monitored dissociated anaesthesia. This examination is conducted in the child's hospital residential school environment. Analysis of these assessments shows a high incidence of pathological defects, strabismus, nystagmus, cataract and refractive errors. These findings are similar to the experience of an overseas clinic. A plea is made for early ocular examination in the first year of life in the suspected neonate to help establish a general diagnosis, prepare a plan of management and prevent secondary retardation.