27
Prevalence and pattern of inheritance abnormalities
PREVALENCE AND PATTERN OF INHERITANCE OF ABNORMALITIES RESULTED FROM CONSANGUINEOUS MARRIAGES IN BAGMARA (RAJSHAHI), BANGLADESH
Md. Anisur Rahman*
Department of Zoology, University of Rajshahi, Rajshahi-6205, Bangladesh
*Correspondence: e-mail:
Abstract: The present study assessed the current prevalence of abnormal characters and their pattern of inheritance resulting from first cousin marriages in Bagmara, Rajshahi, Bangladesh. Four types of consanguineous marriages (first cousin) such as marriage between son and daughter of sister and sister, brother and sister, sister and brother and brother and brother were studied in 31 families. Son and daughter or daughter and son marriages were studied for the expression of abnormalities among the children they produced from 20 families of distant relations. Results revealed that first cousin marriages showed expressivity of certain abnormalities i.e., baldness (1.25%), cleft lip (2.50%), deaf and dumb (3.75%), mental retardation (1.25%), polydactyly (3.75%), and squint eyes (2.50%) among the children of consanguineous couples whereas paralysis (2.08%) was found in only one individual in all the children of distant couples. The prevalence of abnormalities in marriage between son and daughter of sister and sister was 22.22%, brother and sister 15.00%, sister and brother 12.00% and brother and brother 11.76%. Children from consanguineous marriages had a higher percentage (15.00%) of abnormalities than that of the distant relations' marriages (2.08%). In both cases, however, the abnormalities showed autosomal recessive pattern of inheritance.
Keywords: Consanguineous marriage, first cousin, abnormalities, inheritance pattern
mvivskt Avgv‡`i mgv‡R cvwievwiK e¨e¯’vq wbKU AvZ¥xq weevn GKwU ¸i“Z¡c~Y© we‡eP¨ welq| eZ©gvb Aa¨qbwUi D‡Ïk¨ wQj cÖ_g KvwRb weev‡ni d‡j D™¢yZ A¯^vfvweK ˆewkó¨vejxi PjwZ we¯—vi Ges Zv‡`i mÂvi‡Yi aiY wbY©q Kiv| 31wU cwiev‡i Pvi ai‡bi wbKU AvZ¥xq weevn (cÖ_g KvwRb)-Lvjv‡Zv fvB-‡evb, gvgv‡Zv fvB I dzdv‡Zv †evb, dzdv‡Zv fvB I gvgv‡Zv †evb Ges PvPv‡Zv fvB-†evb Aa¨qb Kiv nq| `~i AvZ¥xq‡`i weev‡ni d‡j mš—vb‡`i g‡a¨ A¯^vfvweKZvi cÖKvk Rvbvi Rb¨ 20wU cwievi Aa¨qb Kiv nq| djvd‡j cÖ_g KvwRb weev‡ni d‡j wbKU AvZ¥xq RywU‡`i mš—vb‡`i g‡a¨ KwZcq A¯^vfvweKZv, †hgb gv_vq UvK (1.25%), KvUv †VuvU (2.50%), g~K I ewai (3.75%), gvbwlK Aemv` (1.25%), eûAv½yjx (3.75%) Ges †Uiv †PvL (2.50%) †`Lv hvq Ges `~i m¤ú‡K©i RywU‡`i mš—vb‡`i g‡a¨ ïaygvÎ GKR‡bi c¨vivjvBwmm (2.08%) ˆewkó¨wU †`Lv hvq| Lvjv‡Zv fvB-†ev‡bi g‡a¨ weevn n‡j mš—vb‡`i g‡a¨ A¯^vfvweKZvi we¯—vi nq 22.22%, gvgv‡Zv fvB I dzdv‡Zv †evb n‡j 15.00%, dzdv‡Zv fvB I gvgv‡Zv †evb n‡j 12.00% Ges PvPv‡Zv fvB-†evb n‡j 11.76%| wbKU AvZ¥xq weev‡ni d‡j mš—vb‡`i g‡a¨ (15.00%) `~i m¤ú‡K©i AvZ¥xq‡`i weev‡ni d‡j mš—vb‡`i (2.08%) †P‡q AwaK A¯^vfvweK ˆewkó¨ cÖKvwkZ nq Ges Dfq †¶‡Î A¯^vfvweKZv¸wj A‡Uv‡Rvgvj cÖ”Qbœ ˆewkó¨ wn‡m‡e mÂvwiZ nq|
27
Prevalence and pattern of inheritance abnormalities
Introduction
A marriage is said to be consanguineous (Latin. con- shared and sanguis- blood) when the union is between two people, genetically related by descent, from a common ancestor. In all human societies such as primitive or geographically isolated, the mating between parents and children and brothers and sisters (incest) is prohibited. The children of consanguineous marriages have genetic disorders, like physical deformities,heart disease,mental retardation, deafness,perinatal mortality, andblindness(Auburn Hospital Report 2006). First cousin marriage means that the mating between individuals who are not full sibs but have common grand parents.
The abnormalities are descended from the nature of genes viz., autosomal dominant, autosomal recessive or sex linked recessive of their ancestors. The relatives share a higher proportion of their genes than do unrelated people and this is why related parents will both be carriers of the same recessive gene, and therefore their children are at a higher risk of a genetic disorder or abnormality. The risk is greater when the parents are close relatives but lower for more distant relatives such as second cousins (Kingston 2002). Two unaffected people (carriers) who each carries one copy of the mutated gene have a 25% chance with each pregnancy of having a child affected by the disorders e.g. cystic fibrosis, sickle-cell anemia, wet versus dryearwax (Griffiths et al. 2012).
Consanguineous couples and their offspring account for approximately 10% of the global population (Teeuw et al. 2010). The prevalence of consanguinity varies widely within and between populations and communities, depending on ethnicity, religion, culture and geography and this close relations are available in emigrant communities from highly consanguineous countries and regions such as Pakistan, Turkey, North Africa and Lebanon, now resident in Europe, North America and Australia (Schulpen et al.2006; Hamamy et al.2011).
Bangladesh is a densely populated country of about 160 million people where 90% inhabitants are Muslims (The World Factbook 2014). From the very beginning the people of this area were influenced by the religious thoughts and cultures. The thought of all other religions except Islam discouraged the people of this area to marry close relatives. We know the closer the biological relationship between parents, the greater is the probability that their offspring will inherit identical copies of one or more detrimental recessive genes resulting abnormalities. It has been reported by several workers (Bittles et al.1991; Tadmouri et al.2009; Bittles and Black 2010; Hamamy et al.2011) that consanguineous unions lead to increased expression of autosomal recessive disorders and the cousin marriages provide excellent opportunities for the transmission of characters from parents to offspring (Sandridge
et al.2010). Since cousin mating is very common in our society, the present study therefore was designed to elucidate the prevalence of abnormalities resulting from first cousin consanguineous marriages and their pattern of inheritance found in a population at Bagmara Thana in Rajshahi District. The findings have been compared with the offspring of distant relatives' marriages.
Materials and Methods
In order to collect and analyze information about the patients and their families, a special questionnaire, that included family history, marriage type, information on child development and phenotypical abnormalities, was applied during the survey.
Study area
Five villages with 505 individuals under Bagmara Thana in Rajshahi District were selected for the study of abnormalities in consanguineous (first cousin) and distant marriages. Families were randomly chosen among all the villagers for both types of relation.
Types of mating
There were four types of first cousin marriages such as sons and daughters of sister and sister, those of brother and sister, sister and brother and brother and brother. For distant marriages, couples consisting of sons and daughters or vice-versa were considered.
Case-control study
A case-control study was conducted in the present survey. Cases were defined as consanguineous couples that had children with abnormalities and controls as distant couples that had no affected children. There were 31 case couples and 20 control couples in the investigation.
Abnormalities in children
Parents having children that bore genetic defects were asked for their marriage types individually. Families were surveyed for the incidence of genetic diseases where 31 partners were closely related and 20 distantly related. Seven abnormal characters mentioned below were studied and recorded properly.
Bald head: It is known as “androgenetic alopecia” and is the most prevalent type of hair loss in males.
Cleft lip: A cleft lip is an opening extending through the upper lip resulting from the abnormal facial development duringgestation. It may be in the midline (center) or left and/or right side of the lip.
Deaf and dumb: Deafness is the impaired hearing and dumbness is the lacking of the power of speech of human, meaning unable to hear and speak.
Mental retardation: It is a developmental disorder characterized in varying degrees by a subnormal ability to learn, a substantially low IQ, and impaired social adjustment.
Paralysis: It is aloss of muscle functionin part of the body which can be partial or complete, temporary or permanent, and localized or generalized.
Polydactyly: It is a condition where an individual has more than five digits per hand or foot.
Squint eyes: The medical term for squint eyes is strabismus where the eyes do not look in the same direction.
Photography
Photographs of the abnormal persons were taken by using a cell phone camera (Nokia C2, 2MP).
Results
Among 80 children from 31 consanguineous marriages 12 children had various abnormalities. Whereas from 20 families where marriages occurred between the unrelated persons, only one child out of 48 children was abnormal. The total percentage of abnormalities found in the offspring was 15.00 for consanguineous and 2.08 for distant marriages (Table 1).
The expression of abnormalities
There were six abnormalities i.e. bald head, cleft lip, deaf and dump, mental retardation, polydactyly and squint eyes (Fig. 1) resulting from cousin mating and their frequencies were 1.25%, 2.50%, 3.75%, 1.25%, 3.75% and 2.50% respectively (Table 1). Only one child with paralysis (2.08%) was recorded from distant couples (Table 1 and 2).
Marriages between sons and daughters of two sisters having common parents
Table-2 shows the defects occurred in the offspring caused by the consanguineous marriages between son and daughter of two sisters. From seven families there were 18 children and four of them were abnormal with bald head, cleft lip, deaf and dump and mental retardation. The percentage of abnormality was 22.22.
Marriages between sons and daughters of brother and sister having common parents
Table-2 shows the abnormalities occurred in the offspring caused by the consanguineous marriage between son and daughter of brother and his sister who had common grandparents. 20 children from eight families were recorded and of them three were abnormal for different abnormal characters such as deaf and dumb, polydactyly, and squint eyes. Due to close mating the percentage of the abnormalities was 15.
Marriages between sons and daughters of sister and her brother having common parents
Abnormalities occurred in the offspring by such marriages between son and daughter of sister and her brother is shown in Table 2. Nine families were detected to have three children among 25 with abnormality like cleft lips, polydactyly and squint eyes. The estimated percentage of these defects was 12.
Marriages between sons and daughters of two brothers having common parents
Abnormalities occurred in the offspring caused by the consanguineous marriages between son and daughter of two brothers were studied in seven families and are shown in the Table 2. There were 17 children and among them two were genetically defected bearing deaf and dump and polydactyly characters. The percentage of the defects was 11.
Marriages between son and daughter or vice-versa of unrelated parents
The abnormalities occurred in the offspring caused by the marriage between unrelated persons or distant relations are shown in Table 2. 20 families of the type were studied and 48 children were recorded from those families out of which one child was abnormal i.e. paralyzed body. So the percentage of defect was 2.08.
Discussion
The consanguineous marriage rates vary widely between and within different countries, with religious, ethnic, and local or tribal traditions. In Christianity, the Orthodox churches prohibit consanguineous marriage (Bittles et al. 2001). A similar degree of non-uniformity exists in Hinduism where marriages are prohibited between biological kin for approximately seven generations on the male side and five generations on the female side (Kapadia 1958). The Sikh religion forbids consanguineous marriage, although some minority Sikh groups appear to exercise flexibility in the observance of this proscription (http://www.consang.net/index.php/
Summary).
Most of the people are Muslim in our country and the first cousin marriages are very common and customary. Such marriages take place for a strong family tradition or the maintenance of family structure and property, for the strengthening of family ties or financial advantages relating to dowry or bride wealth payments or the ease of marital arrangements and a closer relationship between the wife and her in-laws or for greater marriage stability and durability as described earlier by several workers (Bittles 1994; Hussain and Bittles 1999).
The recessive traits can be expressed only in homozygous conditions and the frequency of the recessive gene expression increases in the way of consanguineous marriages. The mating couples being carriers will not display any signs that they are carriers, and so may be unaware that they carry the mutated genes. Homozygosity of recessive genes from carrier parents expresses its harmful effects as abnormalities to the children and they are regarded as the genetic defects. As relatives share a proportion of their genes, it is much more likely that related parents will be carriers of an autosomal recessive gene, and therefore their children are at a higher risk of an autosomal recessive disorder or the abnormal phenotypic characters and sometimes it may cause the death of the offspring (Ober et al. 1999). Consanguinity is also an important risk factor in susceptibility to infectious diseases in humans (Lyons et al. 2009). The risk is greater in mating relationships where the parents are close relatives, but for more distant relatives, for example, second cousins, the risk is lower (Kingston 2002). In the present study it was found that no parents were affected by such abnormalities but some of their offspring showed the presence of genetic defects. Thus the abnormalities under study showed autosomal recessive fashion for their transmission.
The products of such close marriages tend to produce an increase in various genetic disorders such as birth defects, mental retardation, deafness and blindness (Jayasekara 1995) and they lead to increased expression of autosomal recessive disorders (Bittles et al.1991; Tadmouri et al.2009; Bittles and Black 2010; Hamamy et al.2011). First cousins are predicted to share 12.5% (1/8) of their characters and thus, on average, their progeny will be homozygous at 6.25% (1/16) of gene loci (Bennett et al.2002). The present study revealed that the first cousin marriages produced 15% abnormalities which are consistent with aforesaid researchers output.
The present results revealed that there were highest percentages (22.22 %) of genetic abnormalities in the consanguineous marriages occurred between son and daughter or daughter and son of two sisters (Table 2). There were bald head, cleft lip, deaf and dump and mental retardation as abnormal characters (Fig. 1) under study. Marriage between son and daughter of brother and his sister had deaf and dumb, polydactyly and squint eyes abnormalities and it showed a 15% abnormality whereas son and daughter of sister and her brother showed cleft lip, polydactyly, and squint eyes with 12% prevalence. 11.76% abnormality found as deaf and dumb and polydactyly from marriage between son and daughter of two brothers. However, there was only a single case of paralysis (2.08%) from mating between son and daughter or daughter and son of unrelated marriages.