Abstract : Mental retardation (MR) is a condition of arrested or incomplete development of the mind, characterized by impairment of skills (cognitive, language, motor and social) manifested during the developmental period, which contribute to overall level of intelligence. Intellectual Disability is a more precise term (used in DSM-V). MR is an etiological factor for development of various co-morbidities, which account for substantial burden of the disease. However, the extent of this co-occurrence varies substantially between reports.

Aim: To study the prevalence of psychiatric and medical comorbidity, among different degrees of Mental Retardation.

Settings and Design: This is a cross-sectional, singlecentered study conducted at the out patient department of Psychiatry, Maharajah’s Institute Of Medical Sciences.

Material & Methods : Sixty-three persons, who came for disability certification, were diagnosed with MR as per ICD-10 criteria, The Wechsler’s Adult Intelligence Scale – IV and The Developmental Screening Test for IQ and Vineland Social Maturity Scale for SQ assessment were used. Psychiatric and medical co-morbidities were diagnosed, using clinical examination, laboratory investigation, the ICD-10 Diagnostic criteria and CHA-PAS SCALE.

Statistical Analysis : The statistical analysis was done by using the Statistical Package for Social Sciences (SPSS) 13.0 version. Frequency, percentages and chi square analysis were used to analyze the data. Result : Out of 63, 40 were found to have medical co-morbidity, while 38 were found to have psychiatric co-morbidity. Severe and profound MR was almost always associated with medical co-morbidities, while mild to moderate MR with psychiatric illness. Different co-morbid disorders were analyzed and discussed.

Conclusions : Evaluation and diagnosis of co-morbid disorder in different degrees of MR is of paramount importance in order to modify treatment schedules and improve the patient outcomes.

Keywords : Mental retardation, psychiatric co-morbidity, medical co-morbidity

Introduction
There is evidence of recognition and treatment of intellectual disability that dates back to Hippocrates, Galen & the Middle Ages. The modern history for the field of intellectual disability begins in the late 18th century 1. The term co-morbidity indicates co-existence of an index disease with another clinical entity. It is increasingly recognized that co-morbidity is more common among people with intellectual disabilities than among the general population. It has now been clearly documented that the mentally retarded are at a greater risk of developing psychiatric disorders (Borthwick- Duffy & Eyman, 1990) 2 and medical illness. Dual diagnosis refers to the joint occurrence of mental retardation and psychiatric disorders. The rates of dual diagnosis have varied from 31% to 100% across various studies (Jacobson, 1982) 3. Indian review of results of previous studies on co-morbidities stressed on mood disorder (8%), hyperkinetic disorder (14%), autism (11%), psychosis (11%), conduct disorder (2%) enuresis (2%) and unspecified emotional and behavioral disorder (26 %)4, mostly not based on any scale but rather the examiners expertise and the ICD-10 & DSM-IV diagnostic guidelines. A Taiwan study using a structured questionnaire indicated that nearly half (47.7%) of the subjects with MR had an associated co-morbid medical or psychiatric illness. A population-based study using a Learning Disability Register in the UK reported that the prevalence of epilepsy was 26% in adults with intellectual disabilities. In view of the common interface of medical and mental-health problems in mentally retarded, initiatives should be taken to enhance their healthcare following a multidisciplinary approach, laying emphasis on dual diagnosis and diagnostic overshadowing. Since there is inconsistency among various reports of occurrence of comorbidities in MR, this study has been conducted.

Aims & Objectives:
To study the prevalence of psychiatric and medical comorbidity, in persons with different degrees of mental retardation.

Materials and Methods:
This is a cross-sectional, single-centered study conducted in the Psychiatry Out-Patient Department of a tertiary care General Hospital, from February 2013 to May 2013. Sixty three persons, who came for disability certification, were taken into the study after obtaining the informed consent from the concerned. The data was recorded in a semistructured proforma and included socio-demographic profile, primary assessment including case history, complete physical and mental status examination. All subjects included in this study were between 5 years and 60 years. Diagnosis of mental retardation was made as per ICD-10 classification. The degree of retardation was assessed based on the intelligence quotient and social quotient by using the following tests:- Developmental Screening Test5 : It was developed by Bharath Raj (1977, 1983) and consists of 88 items, which represent the behavioral characteristics of respective age levels, from birth to 15 years of age. At each age level, items are drawn from behavioral areas, like motor development, speech, language, and personal-social development. Appraisal of the child can be done in semistructured interview with a parent. The IQ calculator incorporated with the test folder helps in ready computation of IQ from mental age and the chronological age. DST showed very high positive correlation +0.7215 to +0.9968 with other intelligence or developmental tests. Inter-scorer reliability (+0.928) and test retest reliability (+0.98) were also found to be high and satisfactory. The Wechsler Adult Intelligence Scale - IV6 : It is a standardized scale developed by David Wechsler and revised by Pearson and was released in 2008. It is composed of 10 core sub-tests and five supplemental subtests, with the 10 core sub-tests comprising the Full Scale IQ. It measures IQ in individuals aged 16–90 years. It takes 60-90 minutes to evaluate. The web based evaluation and scoring option was used to interpret the index and subtest level scale scores. Vineland Social Maturity Scale-Indian Adaption7: It was developed by J Bharath Raj Mallin and was published in 1984. It is an 89-item questionnaire assessing 4 domains. It takes 20-40 minutes to administer and evaluates the social age, social quotient and adaptive functioning ranging from 0 -15 years. E.A. DOLL originally devised the VSMS in 1935 and since then this test is being used in many parts of the world. The administration should be carried out in a semi-structured informal atmosphere. At the end of assessment Full and Half credits may be counted. If the total score falls exactly on the last item of an age level, the patient is given the full Social Age at that age level. The procedure for obtaining the Social Age from the Raw is as follows. S.Q = (Social Age / Actual Age) X 100 The interpretations of S.Q are on similar lines as that of I.Q Except that S.Q has a social life reference. Research studies (Goulet and Barelay 1962)16, have shown a consistent and high correlation between VSMS Social Age (S.A) and the Stanford Binet M.A DOLL reported a correlation of + = 0.85 and Patterson (1943) reporting a correlation of + = 0.96 with the Binet scale on a sample of normal children. The patients were divided into 4 groups depending on the degree of retardation, as per ICD-10, which were asfollows: -

A. Mild Mental Retardation (IQ range 50 to 69)
B. Moderate Mental Retardation (IQ range 35 to 49)
C. Severe Mental Retardation (IQ range 20 to 34)
D. Profound Mental Retardation (IQ range less than 20)

All these were evaluated for the presence of any co-morbid psychiatric illness using the CHA-PAS scale and ICD-10. The Child and Adolescent Psychiatric Assessment Schedule (CHA-PAS)8 is a semi-structured clinical interview developed by Steve Moss, Robin Friedlander and Pauline Lee, first published in 2007. It is a 97-item questionnaire covering 8 domains, namely anxiety disorder, depressive episode, manic episode, OCD, psychosis, ADHD, conduct disorder and autism spectrum disorder. It is a four-point scale constructed around ICD- 10 and DSM-IV criteria, with strong diagnostic indications. The CHA-PAS score form enables two different clinical episodes to be rated on the same form with a provision to interview a second informant to generalize findings. It uses a scoring system that provides a single score for each diagnostic category and each of the categories has a corresponding threshold. If the person reaches or exceeds the threshold it is probable that they warrant a diagnosis in that category. Due to age disparity and to maintain uniformity this scale was selected. Other psychiatric disorders were diagnosed based on the ICD-10 criteria.
A complete physical examination with necessary laboratory investigations was than to assess the presence of co-morbid medical conditions like epilepsy, infectious diseases, hearing impairment, tuberous sclerosis, cerebral palsy, bowel & bladder incontinence, hypothyroidism, recurrent fever, orthopedic handicap, cleft lip & cleft palate, plexiform neurofibromatosis, mucopolysaccharidosis, sexual dysfunction, asthma and enuresis.