Mental retardation: genetic findings, clinical implications and research agenda

Familial risk and heritability of intellectual disability: a population-based cohort study in Sweden

BACKGROUND

Intellectual disability (ID) aggregates in families, but factors affecting individual risk and heritability estimates remain unknown.

METHODS

A population-based family cohort study of 4,165,785 individuals born 1973-2013 in Sweden, including 37,787 ID individuals and their relatives. The relative risks (RR) of ID with 95% confidence intervals (95% CI) were obtained from stratified Cox proportional-hazards models. Relatives of ID individuals were compared to relatives of unaffected individuals. Structural equation modeling was used to estimate heritability.

RESULTS

Relatives of ID individuals were at increased risk of ID compared to individuals with unaffected relatives. The RR of ID among relatives increased proportionally to the degree of genetic relatedness with ID probands; 256.70(95% CI 161.30-408.53) for monozygotic twins, 16.47(13.32-20.38) for parents, 14.88(12.19-18.16) for children, 7.04(4.67-10.61) for dizygotic twins, 8.38(7.97-8.83) for full siblings, 4.56(4.02-5.16) for maternal, 2.90(2.49-3.37) for paternal half-siblings, 3.03(2.61-3.50) for nephews/nieces, 2.84(2.45-3.29) for uncles/aunts, and 2.04(1.91-2.20) for cousins. Lower RRs were observed for siblings of probands with chromosomal abnormalities (RR 5.53, 4.74-6.46) and more severe ID (mild RR 9.15, 8.55-9.78, moderate RR 8.13, 7.28-9.08, severe RR 6.80, 5.74-8.07, and profound RR 5.88, 4.52-7.65). Male sex of relative and maternal line of relationship with proband was related to higher risk (RR 1.33, 1.25-1.41 for brothers vs. sisters and RR 1.49, 1.34-1.68 for maternal vs. paternal half-siblings). ID was substantially heritable with 0.95(95% CI 0.93-0.98) of the variance in liability attributed to genetic influences.

CONCLUSIONS

The risk estimates will benefit researchers, clinicians, families in understanding the risk of ID in the family and the whole population. The higher risk of ID related to male sex and maternal linage will be of value for planning and interpreting etiological studies in ID.

Role of Genetics in the Etiology of Autistic Spectrum Disorder: Towards a Hierarchical Diagnostic Strategy

Progress in epidemiological, molecular and clinical genetics with the development of new techniques has improved knowledge on genetic syndromes associated with autism spectrum disorder (ASD). The objective of this article is to show the diversity of genetic disorders associated with ASD (based on an extensive review of single-gene disorders, copy number variants, and other chromosomal disorders), and consequently to propose a hierarchical diagnostic strategy with a stepwise evaluation, helping general practitioners/pediatricians and child psychiatrists to collaborate with geneticists and neuropediatricians, in order to search for genetic disorders associated with ASD. The first step is a clinical investigation involving: (i) a child psychiatric and psychological evaluation confirming autism diagnosis from different observational sources and assessing autism severity; (ii) a neuropediatric evaluation examining neurological symptoms and developmental milestones; and (iii) a genetic evaluation searching for dysmorphic features and malformations. The second step involves laboratory and if necessary neuroimaging and EEG studies oriented by clinical results based on clinical genetic and neuropediatric examinations. The identification of genetic disorders associated with ASD has practical implications for diagnostic strategies, early detection or prevention of co-morbidity, specific treatment and follow up, and genetic counseling.

Correspondence between Parent and Adolescent Ratings of Life Satisfaction for Adolescents with and without Mental Disabilities

Using a self-report measure of multidimensional life satisfaction reports, the Multidimensional Students' Life Satisfaction Scale (MSLSS; Huebner, 1994), the correspondence between parent and adolescent ratings of life satisfaction was investigated with 80 high school students with mild mental disability (MMD) and a matched sample of 80 normally achieving students. The results revealed acceptable levels of correspondence between parent and normally achieving adolescent ratings, but not for adolescents with MMD. The lack of correspondence between parents and adolescents with MMD suggests possible differences with respect to rater accuracy or differences in the meaning of life satisfaction reports of adolescents with MMD and their parents. Potential users of life satisfaction measures, such as the MSLSS, should be cautious in interpreting the meaning of reports of students with special needs. The comparability of subjective well-being reports of adolescents with and without disabilities should not be assumed, the meaning of reports of normally achieving students may not generalize to particular groups of students with special needs (e.g., students with learning and or behavioral disabilities).

Children with learning disabilities

Children with learning disabilities can present numerous challenges in the acute hospital setting. This review article examines the causes and presentations of learning disability, and considers some of the management strategies employed when these children present for surgery.

Sleep cycling alternating pattern (CAP) expression is associated with hypersomnia and GH secretory pattern in Prader–Willi syndrome

BACKGROUND AND PURPOSE

Hypersomnia, sleep-disordered breathing and narcoleptic traits such as rapid eye movement (REM) sleep onset periods (SOREMPs) have been reported in Prader-Willi syndrome (PWS). In a group of young adult patients with genetically confirmed PWS we evaluated sleep and breathing polysomnographically, including cycling alternating pattern (CAP), and we analyzed the potential interacting role of sleep variables, sleep-related breathing abnormalities, hypersomnia, severity of illness variables and growth hormone (GH) secretory pattern.

PATIENTS AND METHODS

Eleven males and 7 females (mean age: 27.5+/-5.5 years) were submitted to a full night of complete polysomnography and the multiple sleep latency test (MSLT). GH secretory pattern was evaluated by a standard GH-releasing hormone plus arginine test. Sixteen non-obese healthy subjects without sleep disturbances were recruited as controls.

RESULTS

Compared to controls PWS patients showed reduced mean MSLT score (P<0.001), reduced mean latency of sleep (P=0.03), increased REM sleep periods (P=0.01), and increased mean CAP rate/non-rapid eye movement (NREM) (P<0.001). Only four PWS patients had apnea/hypopnea index (AHI)>or=10. Conversely, significant nocturnal oxygen desaturation was frequent (83% of patients) and independent from apneas or hypopneas. In the PWS group, CAP rate/NREM showed a significant negative correlation with MSLT score (P=0.02) independently from arousals, respiratory disturbance variables, severity of illness measured by Holm's score or body mass index (BMI). PWS patients with CAP expression characterized by higher proportion of A1 subtypes presented less severe GH deficiency (P=0.01).

CONCLUSIONS

Our study suggests a relationship between hypersomnia and CAP rate, and between CAP expression and GH secretory pattern in PWS, possibly reflecting underlying central dysfunctions.

Specific Genetic Disorders and Autism: Clinical Contribution Towards their Identification

Autism is a heterogeneous disorder that can reveal a specific genetic disease. This paper describes several genetic diseases consistently associated with autism (fragile X, tuberous sclerosis, Angelman syndrome, duplication of 15q11-q13, Down syndrome, San Filippo syndrome, MECP2 related disorders, phenylketonuria, Smith-Magenis syndrome, 22q13 deletion, adenylosuccinate lyase deficiency, Cohen syndrome, and Smith-Lemli-Opitz syndrome) and proposes a consensual and economic diagnostic strategy to help practitioners to identify them. A rigorous initial clinical screening is presented to avoid unnecessary laboratory and imaging studies. Regarding psychiatric nosography, the concept of "syndromal autism"--autism associated with other clinical signs should be promoted because it may help to distinguish patients who warrant a multidisciplinary approach and further investigation.

Elevated rates of schizophrenia in a familial sample with mental illness and intellectual disability

BACKGROUND

It is unknown whether intellectual disability (ID) is more familially related to psychotic mood disorders or schizophrenia. L. S. Penrose's large sample of families with two or more members admitted to psychiatric hospitals provided a unique opportunity to investigate the familial relationship between mild ID, schizophrenia and psychotic affective disorders.

METHOD

There were 183 affected relative pairs comprising probands with mild ID (95 male, 88 female) and their first or second degree relatives with schizophrenia or psychotic affective disorder.

RESULTS

There were nearly twice as many relatives with a diagnosis of schizophrenia (n = 121) as relatives with affective disorders (n = 62) among the intellectually impaired probands. This excess of schizophrenia was statistically significant, even after accounting for the increased risk of hospitalization for schizophrenia (P = 0.005), and was fairly constant across the different relative types. First-degree relatives with either mental illness were more likely to be parents (n = 77) than siblings (n = 51) or children (n = 3), but there was no excess of mother-son pairs.

CONCLUSIONS

These results suggest a stronger familial relationship of ID with schizophrenia than psychotic affective disorder, and lend some support to the neurodevelopmental hypothesis of schizophrenia.

Learning disability

Learning disability is common, affecting 1-2.5% of the general population in the Western world, and encompasses many different conditions. It usually leads to major functional impairment and lifelong need for support and interventions, not the least important of which are medical and health-care services. Rapid progress is being made in the understanding of the cause and pathogenesis of many learning disability syndromes, and these advances are likely to improve targeted interventions in the next decade. Many countries have abolished a learning disability specialty for medical professionals, but there is a great need to revive this niche of medical knowledge. We know little about quality of life and effects on families of people with learning disability, and research is needed to address these issues.

The schizophrenia phenotype in 22q11 deletion syndrome

OBJECTIVE

This study investigated the schizophrenia phenotype in 24 subjects with 22q11 deletion syndrome (22qDS) and schizophrenia (22qDS-schizophrenia), a rare but relatively homogenous genetic subtype of schizophrenia associated with a microdeletion on chromosome 22. Individuals with 22qDS are at genetically high risk for schizophrenia.

METHOD

Standard measures of signs, symptoms, and course of schizophrenia were assessed in 16 adults with 22qDS-schizophrenia who did not meet criteria for mental retardation and in 46 adults with schizophrenia without evidence of 22qDS from a community familial sample.

RESULTS

There were no significant differences in age at onset, lifetime or cross-sectional core positive and negative schizophrenic symptoms, or global functioning between the two groups of patients with schizophrenia. Patients with 22qDS-schizophrenia had higher excitement subscale scores and less lifetime substance use than the comparison patients with schizophrenia, but no significant differences in anxiety-depression symptom severity were found between the groups.

CONCLUSIONS

These findings indicate that the core clinical schizophrenia phenotype would not distinguish individuals with a 22qDS subtype from those with schizophrenia who did not have the 22qDS subtype. The results provide further support for the utility of 22qDS-schizophrenia as a neurodevelopmental model of schizophrenia as well as support for prospective studies of individuals with 22qDS to help identify precursors of schizophrenia.

Language in mental retardation: Individual and syndromic differences, and neurogenetic variation 1Based on a keynote presentation at the Third European Conference on Psychological Theory and Research in Mental Retardation, Geneva, September 1st, 2000

Predominantly non-etiological conceptions have dominated the field of mental retardation (MR) since the discovery of the genetic etiology of Down syndrome (DS) in the sixties. However, contemporary approaches are becoming more etiologically oriented. Important differences across MR syndromes of genetic origin are being documented, particularly in the cognition and language domains, differences not explicable in terms of psychometric level, motivation, or other dimensions. This paper highlights the major difficulties observed in the oral language development of individuals with genetic syndromes of mental retardation. The extent of inter- and within-syndrome variability are evaluated. Possible brain underpinnings of the behavioural differences are envisaged. Cases of atypically favourable language development in MR individuals are also summarized and explanatory variables discussed. It is suggested that differences in brain architectures, originating in neurological development and having genetic origins, may largely explain the syndromic as well as the individual within-syndrome variability documented. Lastly, the major implications of the above points for current debates about modularity and developmental connectionism are spelt out.

Deficiência mental e família: implicações para o desenvolvimento da criança

O conceito de deficiência mental possui uma história que esteve sempre muito próxima das concepções sócio-econômicas e de homem vigentes em uma determinada sociedade. Neste artigo, apresentamos algumas questões para reflexão relativas à concepção de deficiência mental, à importância do ambiente social para o desenvolvimento da criança com deficiência mental e à dinâmica e funcionamento de famílias com crianças deficientes. A compreensão desses três aspectos e de suas inter-relações constitui a base para a promoção da saúde psicológica e o bem-estar destas crianças e de suas famílias. Concluímos que há necessidade de implementar projetos de pesquisa que focalizem a dinâmica e o funcionamento familiar, adotando conceitos apropriados de deficiência mental e de família.

The genetics of autism

OBJECTIVE

To review systematically the empirical evidence for the involvement of genetic risk factors in infantile autism.

METHOD

We aimed at including all relevant papers written in English. We conducted a Medline search in September 2000. In addition we searched the reference lists of related papers.

RESULTS

A relatively small number of reports including family and twin studies, comorbidity, cytogenetic and molecular genetic studies were reviewed.

CONCLUSION

As well family, twin, cytogenetic and molecular genetic studies supported the importance of genetic risk factors in infantile autism. In most individual cases probably at least a few gene variants simultaneously determine the genetic risk. Presently the most interesting chromosome regions concerning the aetiology of autism are chromosomes 7q31-35, 15q11-13 and 16p13.3 which have been suggested by different lines of genetic research.

Referrals, diagnoses, and neuropsychological findings in an outpatient sample of German children and adolescents with brain dysfunction

Although the necessity of outpatient neuropsychological rehabilitation of neurologically impaired children and adolescents is widely accepted, outpatient services, however, are scarcely supplied. Furthermore, there are only a few analyses of the requirement of such services for children and adolescents. This investigation presents the results of an empirical analysis of referral sources, referral diagnoses, demographic characteristics, and neuropsychological findings for an outpatient neuropsychological utilization sample of children and adolescents with brain dysfunction. Finally, suggestions for the further development of adequate rehabilitation programmes are discussed.

Chromosomal abnormalities in a series of children with autistic disorder

In a series of 127 children diagnosed with autistic disorder the karyotypes of 8, on whom data were available, showed the following chromosomal abnormalities: breakage, a 47 XY pattern, trisomy 13, inversion-duplication of chromosome 15, 47 XY, +der (15) (pter q15: p11 pter), 47 XXY and 46 XY, inv (2) (p11:q13pat, 3q+). Compared to those who were not karyotyped or had normal karyotypes, the children with abnormalities, although cognitively more delayed, were not rated as more severely autistic. Facial dysmorphias and minor physical anomalies tended to be more frequent in the chromosomally deviant subgroup. No differences in demographic characteristics or parental ages were evident. Results are consistent with the view of variability of expression of marker chromosome deviations and a greater severity of retardation and symptoms of autism in those affected. The relevance of the findings to a multimodal genetic etiology of autistic disorder is discussed.

Genetic counseling in autism and pervasive developmental disorders

With increasing awareness of the importance of genetic influences on autism, there is now a demand from families with an affected member for advice regarding their risk of having an autistic child. Research evidence currently available makes it possible to give families empirical recurrence risks. It is desirable that this information is imparted by those with joint expertise in the diagnosis and treatment of autism and in the genetics of complex modes of inheritance. A protocol for genetic counseling is described, along with the key elements that influence the recurrence risks given to individual couples. There is a need to give information regarding recurrence risks not only for autism but also for the broader phenotype. In addition, couples may have other issues they wish to discuss, which may influence their reproductive decisions.

Recurrence risks in mental retardation

Despite improvements in diagnostic techniques and progress made in mapping genes associated with syndromal mental handicap, the estimation of recurrence risks in non-syndromal mental retardation is still dependent on empirical data. Unfortunately, few studies are available to guide the clinician and their results differ significantly. For example, recurrence risks to all sibs of a male index patient with severe mental retardation vary between 3.5% and 14% in commonly quoted series. The present review highlights the problems involved in interpreting the previous work in this area and discusses the definition of mental retardation according to the degree of severity, phenotype, and its pattern of inheritance. In planning future studies, an appreciation of these issues should allow us to derive accurate and comparable risk figures for use in counselling affected subjects and their families.

Practitioner review: physical investigations in mental retardation

Mental retardation occurs in more than 1% of the child population. A cause can be found in almost 80% of individuals with severe mental retardation, but in fewer than 40% of those with mild mental retardation. A work-up is indicated in all cases of mental retardation. A medical doctor with specific training in the field is needed to make "decision-tree diagnosis" and to suggest the most appropriate physical investigations in each case. This paper provides practical guidelines for diagnosis and work-up both in severe and mild mental retardation.

Opportunities for psychiatry from genetic findings

BACKGROUND

The opportunities for psychiatry deriving from available or likely genetic advances are reviewed.

METHOD

Clinical implications are considered in the context of both the misconceptions and benefits associated with relevant genetic findings.

RESULTS

Misconceptions include that: heritability estimates have a 'true' fixed value; a high heritability means that environmental interventions will be ineffective; a high heritability within groups means that differences between groups will also be due to genes; genetic effects are determinative; 'genetic' means single abnormal genes; genes associated with disease must be bad and justify eugenic measures; gene therapy will be widely applicable; and genetic screening of the general population will be useful. The benefits include demonstrations that: both genes and environment have an ubiquitous influence; some prevailing diagnostic assumptions are mistaken; genes influence development; the effects of nature and nurture are not separate; and environmental effects tend to be person-specific. The potential value of molecular genetics lies in elucidation of causal processes as they apply to both brain systems and nature-nurture interplay; improving diagnosis and genetic counselling; and the development of improved pharmacological interventions.

CONCLUSION

Advances in genetics will make a major impact on clinical psychiatry, and should bring practical benefits for both prevention and treatment.

Implications of genetic research for child psychiatry

OBJECTIVE

To review implications of genetic research in child psychiatry.

METHOD

Key advances in quantitative and molecular genetics are noted and findings are summarized with respect to autism, attention-deficit hyperactivity disorder, oppositional defiant and conduct disorders, depression, schizophrenia, and Tourette's syndrome.

CONCLUSIONS

Genetic findings will be helpful clinically in the elucidation of disordered brain processes, the understanding of nature-nurture interplay, diagnosis, genetic counselling, and pharmacotherapy.

Psychopathology in infancy

The first three years of life present unique challenges to the study of psychopathology. We highlight four of the issues in a selective review of the developmental psychopathology of early childhood, including lack of specificity of risk and outcome variables, measurement difficulties, rapid developmental changes and the centrality of the relationship context in early childhood. We also highlight issues relevant to conceptualizations of disorders of infancy, emphasizing especially the need for efforts to validate clinical disorders. We consider two major domains of infant development that we believe are especially relevant to a discussion of psychopathology, namely, regulation of emotion and infant-caregiver attachment. Discussions of these two domains of infant development and their psychopathological extremes allow us to consider conceptualizations of psychopathology from the dual perspectives of developmental psychopathology and clinical disorders. We conclude by suggesting a number of strategies to build upon previous research.

Genetic influences on mild mental retardation: concepts, findings and research implications

It has long been known that mild mental retardation (meaning that associated with an IQ in the 50–69 range) shows a strong tendency to run in families and that there is a much increased recurrence risk if either a parent or a sib has mental retardation. For example, Reed & Reed (1965) found that, having had one retarded child, the chance of a further retarded child was 6% if both parents and their sibs were ‘normal’, 13% if both parents were normal but one had a retarded sib, 20% if one parent was retarded, and 42% if both were retarded. A somewhat similar gradient was found in the more recent study by Bundey, Thake & Todd (1989). The appreciation that mild mental retardation was so strongly familial had led Lewis (1933) some years earlier to refer to it as ’subcultural‘ (meaning that it was a normal variation), in order to differentiate it from severe mental retardation, which was viewed as ‘pathological’. Penrose (1938, 1963) made the same classificatory distinction and the utility of a two-group approach became generally accepted (Burack, 1990).

Autism research: prospects and priorities

Research prospects and priorities in the field of autism are discussed with respect to (a) diagnosis, classification, and epidemiology; (b) clinical research; (c) neuropsychological research; (d) genetics; (e) structural and functional brain imaging; (f) postmortem studies; (g) other biological research; and (h) treatment research. Also, it is argued that research into autism has a priority in the broader field of developmental psychopathology because it carries the promise of throwing light on casual mechanisms that apply beyond the syndrome of autism.