A Family Study of Consanguinity in Children with Intellectual Disabilities in Barwani, India

INTRODUCTION

Several determinants have been identified for intellectual disabilities (IDs). The relationship between sociodemographic, biological, environmental, and genetic factors of ID has also been explored in scientific literature. Genetic disorders such as Down syndrome, fragile X chromosome, Cornelia de Lange syndrome, Cri du Chat syndrome, Klinefelter syndrome, XYY, and Prader–Willi syndrome are commonly associated with IDs which may occur due to error in genetic transformation/mapping or mutation.[1234]

ID displays multidimensional arrays with genetic and medical conditions. About 25%–50% causes of ID are attributed to genetic factors.[5] Children closely match with their parents in the genetic, psychological, and physical makeup because they inherit these traits from their parents. Like good characteristics, a defective genetic material also gets inherited through the generation and potentially carries several diseases such as diabetes mellitus, heart diseases, and neurological disorders. The defective or disease-related trait transfers from relatives into their children through consanguineous relationship between the parents. Researchers have found consanguinity to be associated with a high risk for mortality among Muslim children in India and Pakistan.[67] The negative impact of consanguinity has been explored in several studies. Many evidences in literature demonstrate the negative impact of consanguinity. Parents who have ID or parents who married consanguineously with an ID relative can pass on ID in their children.[8] Approximately 90 gene defects have been identified for X-linked ID.[910] However, the translational research has not been successful in applying genetic knowledge for the prevention of ID.[1011]

The occurrence of ID in several families is associated with the presence of ID in a family member.[1213] The consanguineous marriages may be playing a crucial role in transferring ID in children from their ID relatives. Primarily, consanguinity is a social factor. Consanguineous marriages are very common in the world.[14] India also has a high rate of consanguineous marriage. The culture and practice of consanguineous marriage varies with geography, religion, and caste in India. The rate of consanguineous marriages is reported to be as high as 40% in the southern states of India.[1115] Parents with or without ID can receive a defective gene of lower cognitive abilities from their parents with ID. Then, they can pass to their children in the form of ID.[141617] The presence of other neurological disorders such as epilepsy, cerebral palsy, and severe mental illnesses in consanguineous relatives has also been found to be associated with ID in various studies.[141819] A clinical study in South India has found that 30% of children with ID were born from parents who had a consanguineous marriage.[1620]

Considering the fact that the family history of ID is itself a potential cause of ID, an attempt should be made to understand the different patterns of consanguineous marriages and the relationship between ID in children with ID in their parents and consanguineous relatives.[1121]

MATERIALS AND METHODS

This is a case series research design. An extreme sampling method was applied. Under this sampling approach, authors selected six cases of ID with a family history of ID and of consanguineous marriage between their parents, from a pool of 262 ID cases aged between 3 and 18 years. These cases were registered in the Integrated Community-based rehabilitation Disability Project Barwani, Asha gram Trust. This project was implemented in 63 remote villages of Barwani district, Madhya Pradesh, India. All cases were receiving rehabilitation services from this project. Asha gram Trust is a nonprofit organization. It has been providing health and rehabilitation services in Barwani and adjoining districts in Madhya Pradesh. The first author was employed with this organization. He was involved in making diagnosis and providing comprehensive intervention to these cases. Data were collected by the first author. The clinical interviews and case history methods were used for data collection. The first author's informal communication, interaction during training with village groups in project area, and information collected through active participant observation were considered in discussion. Out of all cases of consanguineous marriages and a family history of ID, epilepsy, and mental illness, only six cases, representative of all patterns of consanguineous relationship, were selected for this study. The sample represents tribal and nontribal population. The patterns of consanguineous marriages are shown and described with the help of pedigree charts.

RESULTS

Out of a total of 262 children with ID, parents of 97 (37.02%) children had some form of consanguineous relationship and a family history of at least one disorder from ID, epilepsy, cerebral palsy, and mental illness. Among consanguineous parents, 46 (47.42%) children had a family history of ID, 27 (27.83%) had epilepsy, 10 (10.30%) had cerebral palsy, and 14 (14.43%) had mental illness. Out of the total ID population, 17.55% had a history of ID, 10.30% had epilepsy, 3.81% had cerebral palsy, and 5.35% had mental illness [Table 1 and Figures 1-6].

Table 1 Family history of intellectual disability, epilepsy, cerebral palsy, and mental illness in consanguineous marriages in total sample population of intellectual disability (n=262)

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Figure 1

History of intellectual disability and epilepsy

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Figure 2

History of intellectual disability

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Figure 3

History of intellectual disability, epilepsy, and mental illness

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Figure 4

History of intellectual disability in third and fourth generations

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Figure 5

History of epilepsy, and mental illness

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Figure 6

History of intellectual disability and cerebral palsy

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DISCUSSION

The consanguineous pattern in tribal and nontribal (Hindu) population in our study is consistent with other studies.[11] Like Muslim population, marriages between brother's and sister's children and children of real sisters and real brothers were also found in tribal and nontribal population. Like Muslim population, the preference for the first cousin marriages was observed in Hindus.[2223] The marriage between the children of brother and sister is common in Hindus. However, marriage between the son of sister and her brother's daughter is preferred in Central and North India, whereas marriage between son of brother with his sister's daughter is common in southern states of India. The rate of consanguineous marriages is relatively higher in South India.[1724] Like Hindus and Muslims, consanguineous marriages are equally common in tribal population. Consanguineous marriage equally occurs between son and daughter of brother and sister without any preference in subtribes, such as Bheil, Bhilala, and Barela in Barwani district. Other researchers also found a similar pattern in subtribe Baiga in the state of Madhya Pradesh.[25] Compared to nontribal parents of ID children, the age differences between tribal parents (husbands and wives) were observed higher. In addition, polygamy in tribal males was observed which was rarely noticed in nontribal males. A few marriages between one male with two real sisters were also observed in tribal population. A higher rate of consanguineous marriages in rural nontribal and tribal populations was found consistent with other researchers.[26]

CONCLUSION

Our study demonstrates an association between consanguinity and family history of ID in tribal and nontribal populations from India. Further research employing a case–control design in consanguineous and nonconsanguineous families is needed to better understand the association between ID and family history. There is also a need to create public awareness related to ill effects of consanguinity and its association with ID.