Aetiological factors and prevalence of severe mental retardation in children in a Swedish municipality: the possible role of consanguinity

Migration and risk of intellectual disability with and without autism: A population-based cohort study

OBJECTIVE

To investigate whether parental migration, parental region of origin, timing of child's birth in relation to maternal migration and parental reason for migration are associated with intellectual disability (ID) with and without autism.

METHODS

We used a register-based cohort of all individuals aged 0-17 years in Stockholm County during 2001-2011. General estimating equation logistic model and additionally sibling comparison were used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). The models were adjusted for child's sex and birth year and parental age at child's birth, and additionally for migrant-specific variables in the analyses including only children with migrant parent(s).

RESULTS

Within the eligible sample of 670,098 individuals, 3781 (0.6%) had ID with autism, and 5076 (0.8%) had ID without autism. Compared with children with Swedish-born parents, children with both parents born abroad had an increased risk of ID with autism (OR = 1.6, CI 1.5-1.8) and ID without autism (OR = 1.9, CI 1.7-2.0). Among these children with both parents born abroad, it was protective of ID with autism when the child's birth occurred before and later than four years after maternal migration, which was replicated in the sibling comparison. The associations with both conditions were more pronounced with parental origin in regions comprising low- and middle-income countries and with reasons other than work or study.

CONCLUSIONS

Parental migration is associated with ID regardless of co-occurrence of autism. Our results indicate an association between environmental factors during pregnancy related to migration and offspring ID with autism, although further confirmative studies are needed.

Recessive VARS2 mutation underlies a novel syndrome with epilepsy, mental retardation, short stature, growth hormone deficiency, and hypogonadism

Background

Most mitochondrial and cytoplasmic aminoacyl-tRNA synthetases (aaRSs) are encoded by nuclear genes. Syndromic disorders resulting from mutation of aaRSs genes display significant phenotypic heterogeneity. We expand aaRSs-related phenotypes through characterization of the clinical and molecular basis of a novel autosomal-recessive syndrome manifesting severe mental retardation, ataxia, speech impairment, epilepsy, short stature, microcephaly, hypogonadism, and growth hormone deficiency.

Results

A G>A variant in exon 29 of VARS2 (c.3650G>A) (NM_006295) was identified in the index case. This homozygous variant was confirmed by Sanger sequencing and segregated with disease in the family studied. The c.3650G>A change results in alteration of arginine to histidine at residue 1217 (R1217H) of the mature protein and is predicted to be pathogenic.

Conclusions

These findings contribute to a growing list of aaRSs disorders, broadens the spectrum of phenotypes attributable to VARS2 mutations, and provides new insight into genotype-phenotype correlations among the mitochondrial synthetase genes.

Prevalence of epilepsy among people with intellectual disabilities: A systematic review

PURPOSE

Epilepsy is more common in people with intellectual disabilities than in the general population. However, reported prevalence rates vary widely between studies. This systematic review aimed to provide a summary of prevalence studies and estimates of prevalence based on meta-analyses.

METHOD

Studies were identified via electronic searches using Medline, Cinahl and PsycINFO and cross-citations. Information extracted from studies was tabulated. Prevalence rate estimates were pooled using random effects meta-analyses and subgroup analyses were conducted.

RESULTS

A total of 48 studies were included in the tabulation and 46 studies were included in meta-analyses. In general samples of people with intellectual disabilities, the pooled estimate from 38 studies was 22.2% (95% CI 19.6-25.1). Prevalence increased with increasing level of intellectual disability. For samples of people with Down syndrome, the pooled estimate from data in 13 studies was 12.4% (95% CI 9.1-16.7), decreasing to 10.3% (95% CI 8.4-12.6) following removal of two studies focusing on older people. Prevalence increased with age in people with Down syndrome and was particularly prevalent in those with Alzheimer's/dementia.

CONCLUSION

Epilepsy is highly prevalent in people with intellectual disabilities. Services must be equipped with the skills and information needed to manage this condition.

Aetiology of severe mental retardation and further genetic analysis by high-resolution microarray in a population-based series of 6- to 17-year-old children

AIM

To investigate the prevalence, co-morbidities and aetiologies of severe mental retardation (SMR) in a cohort of Swedish children and to further penetrate aetiologies in the group with undetermined causes by application of updated clinical-genetic methods.

METHODS

The study was population-based and included children living in the County of Halland in western Sweden in 2004 (born 1987-1998; 46,000 children). Patients were identified through habilitation centres, paediatric clinics and school health services. Patients with unclear prenatal aetiology were investigated with single nucleotide polymorphism (SNP)-array.

RESULTS

Severe mental retardation was identified in 133 children from 132 families, corresponding to a prevalence of 2.9 per 1000 children. There were more males than females (90:43).The aetiology was prenatal in 82 (62%), perinatal in 14 (10%) and postnatal in 8 (6%). In 29 (22 %) children, mainly males with autism, the cause could not be related to the time of birth. In the prenatal group, genetic causes dominated, but still 23 children remained undiagnosed; in 5/19 of these patients, a diagnosis could be made after SNP-array analysis. One or more associated neurological handicaps were found in more than half of the children.

CONCLUSION

Prevalence and co-morbidity were similar to previous Scandinavian studies. High-resolution chromosomal micro-array techniques are valuable diagnostic tools, reducing the number of patients with unexplained SMR.

Prevalence of chronic health conditions in children with intellectual disability: a systematic literature review

A systematic review of the prevalence rates of chronic health conditions in populations of children with intellectual disability was provided. We identified 2,994 relevant studies by searching Medline, Cinahl, and PsycINFO databases from 1996 to 2008. We included the 31 studies that had sufficient methodological quality. The 6 most prevalent chronic health conditions in children with intellectual disability were epilepsy (22.0/100), cerebral palsy (19.8/100), any anxiety disorder (17.1/100), oppositional defiant disorder (12.4/100), Down syndrome (11.0/100), and autistic disorder (10.1/100). The reported prevalence rates of chronic health conditions in this population was much higher than in the general population. However, both the number of studies that were included and the number of chronic health conditions they reported about were limited. There is an urgent need for better evidence on the prevalence of chronic health conditions among children with intellectual disability.

The prevalence of neurological disorders in Saudi children: a community-based study

There are limited data on the pattern and prevalence of pediatric chronic neurologic conditions in the region. Therefore, the objective of this study was to establish the prevalence of these disorders in the Kingdom of Saudi Arabia. A multistage probability sampling design was used to select a random sample of Saudi households representative of the Saudi population. A total of 45 682 Saudi children were screened. Of these children, 313 had a chronic major neurologic disorder indicating a prevalence of 68.5 per 10 000 children, which was the highest among all chronic diseases in children. Mental retardation and cerebral palsy were the most common neurologic disorders among Saudi children with a prevalence rate of 26.3/10 000 and 23.4/10 000, respectively. The finding that major neurologic disorders are the most common pediatric chronic disorders in the Kingdom of Saudi Arabia indicates that priority should be given to research and education as well as health care planning.

Prevalence of autism in children born to Somali parents living in Sweden: a brief report

In a geographical area of Stockholm, with a relatively large Somali immigrant population, parents as well as teachers in special schools and staff at habilitation centres have raised concerns over whether children with a Somali background are over-represented in the total group of children with autism. The aim of the study was, therefore, to investigate the prevalence of autism in children with parents from Somalia, living in Stockholm county, and to compare the prevalence in children of Somali background with that in the non-Somali group. We reviewed the records of 17 children (13 males, four females), born between 1988 and 1998 (age range 7-17y) and with a Somali background, who had a diagnosis of autistic disorder or pervasive developmental disorder not otherwise specified (PDDNOS) and were registered at either of the two autism habilitation centres for school-aged children. The prevalence of autistic disorder or PDDNOS was found to be three to four times higher than in the non-Somali group (0.7% vs 0.19%). All children also had learning disability.* Our findings warrant further investigations of possible aetiological factors behind the increased prevalence of autistic disorders in children of Somali origin found in this area in Sweden.

Consanguineous unions and child health in the State of Qatar

The aim of the study was to estimate the prevalence and sociodemographic predictors of consanguineous unions in the State of Qatar and to assess the association between consanguinity, fertility and child health. A representative sample of 1800 Qatari women aged > or =15 years was approached for the study. Of these, 1515 (84.2%) women agreed to participate. The consanguineous marriage rate was 54.0% with estimated population confidence limits of 52.3-55.7%. First cousin unions were the most common form of cousin marriage. The level of parental consanguinity (both in the respondent's parents and her parents-in-law) was quite high. In a multivariable analysis, both education of the respondent and her husband as well as parental consanguinity were found to be strong predictors of consanguineous unions in the index generation. Although fertility was high in both groups, the mean number of pregnancies was somewhat higher in respondents with first cousin unions. Concomitantly they also had a slighter higher rate of livebirths than women in non-consanguineous unions. The occurrence of asthma, mental retardation, epilepsy and diabetes was significantly more common in offspring of all consanguineous than non-consanguineous couples.

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.

Prevalence of intellectual disability in Western Australia

Record linkage of multiple sources was used to ascertain children with intellectual disability born in Western Australia between 1983 and 1992. The prevalence was 14.3 per 1000, 10.6 per 1000 for children with mild or moderate and 1.4 per 1000 for those with a severe level of intellectual disability. Prevalence was greater in males (prevalence ratio 1.6) and in children of Aboriginal mothers (prevalence ratio 2.3). Although prevalence of intellectual disability has been found to vary according to study location, method of ascertainment and criteria used, these estimates are similar to estimates from several recent studies.

The epidemiology of mental retardation: challenges and opportunities in the new millennium

There are a number of problems and challenges in relating the science of epidemiology to mental retardation (MR). These relate to how MR is defined and classified and how these definitions may change over time. These as well as other differences in ascertainment sources and methods need to be considered when comparing MR prevalence over time and place. On the other hand, advances in technology also provide new and efficient methods of data collection both by data linkage and by use of web-based methods to study rare diseases. While prevalence studies have not been individually reviewed, we have examined the range of data including recent studies relating to how prevalence differs according to age, gender, social class and ethnicity. Some problems with available etiological classification systems have been identified. Recent etiological studies, most of which use different classification systems, have been reviewed and explanations have been postulated to account for differences in results. Individual risk factors for MR are considered whilst the option of considering a population as opposed to a high risk strategy to MR prevention is raised. This might well involve improving the social milieu surrounding the occurrence of individual risk factors. The impact of biotechnological advances such as antenatal and neonatal screening and assisted reproduction on MR are discussed. The issue of how inequalities in access to technology may impact on case identification and even have the potential to further widen inequalities is raised. The importance of extending the use of epidemiological tools to study the social, health and economic burden of MR is also emphasized. However, in order to apply to MR the "prevention-intervention-research" cycle, which surely underpins all epidemiology, it is vital to ensure that the methodological challenges we raise are adequately addressed.

[A practical diagnostic approach to mental deficiency in 2002]

The identification of an etiology in children with mental deficiency is a major challenge in routine pediatrics. As the result of a workshop leaded by the Société française de neurologie pédiatrique (SFNP), we propose a three steps diagnostic procedure, taking into account several frequent clinical observations leading to further targeted investigations. The yield of systematic imaging and biological screening remains very low, when performed for a non specific isolated mental retardation, without any characteristic clinical features. Yet, it is mandatory for an accurate genetic counseling to know not only the clinical diagnosis of developmental delay, but also the pathophysiology and the underlying molecular mechanism. The SFNP's proposal points out the necessity of a comprehensive clinical process including cautious neurodevelopmental assessment, reliable cognitive and adaptive skills evaluation, and collaboration between different specialists.

Lay perceptions of genetic risks attributable to inbreeding in Pakistan

Pakistan along with many other West and South Asian countries has a very high prevalence of consanguineous, especially close cousin, marriages. Although there is substantial empirical information on offspring morbidity and mortality attributable to parental consanguinity, population-based information on how communities in general, and women in particular, perceive the health risks associated with consanguineous unions is limited. This paper considers community perceptions of health effects associated with consanguineous marriages using qualitative data from 15 focus group discussions and 294 in-depth interviews. The study was conducted in four low-income, multi-ethnic, and multi-religious communities in Karachi, the principal commercial center of Pakistan. The results show a general lack of awareness of the possible adverse health effects of consanguineous marriage. In cases where a link between consanguinity and ill health was acknowledged, it often centered on the familial origins of non-communicable disorders such as diabetes and hypertension or infectious diseases such as tuberculosis. Belief in fate and the "evil eye" was widespread across all ethnic and religious groups. Many respondents did not agree with medical explanations of a genetic mode of disease inheritance, even in cases where there was an affected child in the family. The absence of a uniform manifestation of disease among all children of a couple who were identified as carriers of a specific mutation added to the confusion among participants. The study highlights the need for further quantification of risks associated with consanguinity and a need for provision of appropriate information to primary-care clinicians and also to communities. The likely impact of increasing morbidity attributable to inbreeding on the health care system in resource poor settings is also discussed.

Consanguinity and its relevance to clinical genetics

Marriage between close biological relatives is generally regarded with suspicion and distaste within Western society, reflecting historical and religious prejudice. By comparison, in many other populations there is a strong preference for consanguineous unions, most frequently contracted between first cousins, and marriage outside the family is perceived as a risky and disruptive option. The increasing importance of the genetic contribution to the overall disease profile in both developed and developing countries has highlighted potential problems associated with detrimental recessive gene expression in consanguineous progeny. This review examines the outcomes of consanguineous unions, with proposals as to how the ongoing preference for consanguinity in many communities can best be accommodated from a clinical genetics perspective.