**1. Introduction**

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*tional & Developmental Psychology*, *11*, 11–25.

*Adolescent Psychiatry*, *41*(5), 572–9.

The autism spectrum disorders (ASD) represent a group of severe and chronic neuro-devel‐ opmental disorders often simply referred to as autism. [1] Using the criteria provided by the *Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition*, ASD are diagnosed by impairments within the three strands of DSM-4: *social interaction, communication* and *repetitive behaviours or interests*. [2] The aetiology of autism is complex. [3] Research has implicated a strong genetic basis [4-7] involving multiple genes [5, 7, 8] and possible gene-environment interactions. [9-13] Advances in chromosomal microarray analysis and gene sequencing technologies have improved diagnoses and suggest that aetiologies of ASD will continue to be uncovered. [9] In addition, a child presenting with autistic symptoms may be found to have a certain genetic mutation which accounts for their true underlying biological diagnosis. For example, a diagnosis of Rett syndrome would be confirmed when a girl with ASD and intellectual disability was found to have a mutation of the *MECP2* gene on the X-chromosome. [14] Children with ASD and intellectual disability have been found to have an expansion of the *FMR1* gene confirming a diagnosis of Fragile X syndrome. [15]

Autism and intellectual disability commonly coexist with 30-80% of persons with ASD reported as also having ID. [16, 17] Currently, the relationship between ASD and comorbid ID is poorly understood. [18] However, it is known that phenotypically, persons with these disorders can be grouped into the three categories of ASD without ID, ASD with ID and ID only. [18] Intellectual disability (ID) is characterized by an intelligence quotient (IQ) of less than 70 which is associated with limitations in at least two areas of adaptive skill and which

© 2013 Fairthorne et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

is manifest before 18 years. [19] The level of ID is generally grouped into the five levels of mild, moderate, severe, profound and unspecified by IQ score. In research it is common to stratify ID to the following three levels defined by the American Psychiatric Association [2] (Table 1).

Phenotype [31] and includes qualitatively similar, but milder traits in areas such as language, personality and social behaviour. Some researchers believe that identification of the Broad Autism Phenotype in family members might provide a complementary strategy for detecting genes which contribute to the likelihood of ASD. [32, 33] When comparing family members of a child with ASD to persons from the general population, subtle differences within the Broad Autism Phenotype could be associated with specific brain regions, particular neural pathways,

Pre-Existing Differences in Mothers of Children with Autism Spectrum Disorder and/or Intellectual Disability: A Review

http://dx.doi.org/10.5772/54488

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The above factors have been used as guides in choosing terms for our literature search to examine pre-existing characteristics of mothers of children with autism and mothers of children with intellectual disability of unknown cause. Inherent characteristics of mothers of children with a specific disability could be associated with the genetic, environmental or genetic-environmental aetiology of their child's condition. It is therefore important to separate pre-existing factors, particularly in relation to mental health, from morbidities such as depression [34] which might develop due to the more intense demands of caring for a child

The aim of this study is to review research on the pre-existing characteristics which differen‐ tiate mothers of children with ASD and/or ID of unknown cause from each other and from mothers of children without these disabilities. Such an investigation may help to further clarify the determinants of ASD and/or ID including the role of genetic and modifiable risk factors. Improving our understanding of the genetic and environmental causes of ASD and ID may reduce the future burden of these disabilities [35] by hastening the development of effective

The papers considered for this review resulted from a search of the Medline, Web of Knowl‐ edge, Scopus and Google scholar databases. Combinations of the search terms below were

**•** Terms associated with ASD and/or ID: autis\*, pervasive development disorder\*, intellectual

**•** Terms associated with ASD and/or ID aetiology: immigra\*, migra\*, ethnic\*, age, sociodemographic, prenatal, perinatal, auto\*, immun\*, anti\*, psych\* and phenotype\*; and

**•** Terms associated with mothers of children with ASD and/or ID: traits, characteristics,

**•** It was accepted for publication between 1st January 1990 and 31st October, 2012 inclusive;

**•** It described new research and was published in a peer-reviewed journal;

and ultimately with particular genes. [33]

with ASD and/or ID.

chosen.

prevention and treatment strategies.

**2. Literature search and selection**

disability, mental retardation, disab\*;

parents, mothers, children, persons.

A paper was included in the review if:

**•** It was a full text article in English;


\*Here the person has been assessed as having ID but has not been assessed adequately to determine the level.

**Table 1.** Levels of intellectual disability

In terms of aetiology, ID can be broadly divided into cases of known biomedical cause and those of unknown cause. The biomedical causes may be divided into genetic and non-genetic causes. Further subdivisions are given in Figure 1.

**Figure 1.** Commonly known aetiologies of intellectual disability

In addition to genetic and non-genetic causes of ASD and ID, relationships with sociodemographic factors such as a mother's education, [20, 21] immigration, [17, 22] and ethnicity, [23] have also been identified. Other reported associations involve aspects of a mother's health including physical characteristics [24] physical [25, 26] and mental health [27, 28] and health behaviours. [29, 30]

It has also been reported that milder autistic traits are present in other family members of individuals diagnosed with ASD. This phenomenon has been coined the Broad Autism Phenotype [31] and includes qualitatively similar, but milder traits in areas such as language, personality and social behaviour. Some researchers believe that identification of the Broad Autism Phenotype in family members might provide a complementary strategy for detecting genes which contribute to the likelihood of ASD. [32, 33] When comparing family members of a child with ASD to persons from the general population, subtle differences within the Broad Autism Phenotype could be associated with specific brain regions, particular neural pathways, and ultimately with particular genes. [33]

The above factors have been used as guides in choosing terms for our literature search to examine pre-existing characteristics of mothers of children with autism and mothers of children with intellectual disability of unknown cause. Inherent characteristics of mothers of children with a specific disability could be associated with the genetic, environmental or genetic-environmental aetiology of their child's condition. It is therefore important to separate pre-existing factors, particularly in relation to mental health, from morbidities such as depression [34] which might develop due to the more intense demands of caring for a child with ASD and/or ID.

The aim of this study is to review research on the pre-existing characteristics which differen‐ tiate mothers of children with ASD and/or ID of unknown cause from each other and from mothers of children without these disabilities. Such an investigation may help to further clarify the determinants of ASD and/or ID including the role of genetic and modifiable risk factors. Improving our understanding of the genetic and environmental causes of ASD and ID may reduce the future burden of these disabilities [35] by hastening the development of effective prevention and treatment strategies.
