High Prevalence of Haemoglobin E in Three Populations of the Malda District, West Bengal, India
M .K . Das, B. Dey, M. Roy, B.N. Mukherjee
A n thropom etry and Human G en etics U n it, Indian Statistical Institute, Calcutta, India
Key Words. H aem oglobin E • P opulation study • In d ia
Abstract. High frequencies o f haem oglobin (H b) E were reported earlier from Assam in northeast India. In the presen t study one o f the three populations of the Malda dis
trict of W est Bengal, called the D eshi, was found to show one of the highest incidences o f the H b E gene (0.61) recorded so far. A fo u n d er effect a n d /o r local inbreeding may possibly explain this observation.
Some populations o f the Tibeto-B ur- m an-speaking Bodo ethnic g ro u p residing in Assam have shown the highest fre
quency (0.64) o f the haem oglobin E (H b E ) gene [Deka et al., 1988], so far, in the w orld. There are alternative h y p o theses regarding the origin, spread and m aintenance o f the gene in sou th east Asia and in northeast India. U ntil recently, the hypothesis o f the single Hb A -*■ H b E m u
tation an d its spread from southeast Asia was generally accepted. It was believed to be m aintained through an ad ap tiv e ad vantage in the m alarious environm ent [Flatz, 1967; Flatz et al., 1972; K ruatra- chue et al., 1969], but a higher incidence o f the gene (0.4-0.6) am ong the Bodo populations th an am ong th e p o p u latio n s
speaking A ustroasiatic or Thai languages - the K hasi a n d the Ahom (0.3-0.4), who could have carried the gene from Thai
lan d o r from Shahn in Burma - could noi be ex p la in ed by this hypothesis. T h e de
m o g rap h ic analyses of some Bodo popu
latio n s have suggested different selective m echanism s in Assam and in Thailand [D eka, 1981; Das and Deka, 1985; Deka et al., 1988]. O n the other hand, th e re ate rep o rts on two different mutations of H b E w ith tw o different DNA frame- w orks [A ntonarakis et al., 1982; Hun- drieser et al., 1988]. In this re p o rt the re
sults o f a study of the Hb E gene fre
quency in three endogam ous p o p u lations o f the n o rth e rn part of West Bengal, who are offshoots o f the Bodo group, are dis
cussed in the light o f this background know ledge.
Fig. 1. Map o f West Bengal, showing the distribution o f the populations under study.
Material and Methods
The Poliya, Deshi and Tiyor p op u lation s h a v e originated from the Koch ethnic group o f the n o rth ern part of the present West Bengal (fig. 1) and A s sam states who are described as one o f the m ost an- cient peoples of India [D alton, 1872]. The P oliya and the Deshi are Bengali-speaking pop u lation s and f o l
low village exogamy. The Tiyors speak ‘K hotta or mixed Hindi dialect’. There are two su b d iv isio n s o f the Poliya, known as Sadhu Poliya and Babu P o liy a ,
an d the D esh i are o n e o f the subcastes o f Sadhu P o
liya. The Sadhu P oliya are traditionally horticultur
ists, and the D esh i are settled agriculturists who claim a superior status. The Tiyor form a subcaste o f the R ajbanshi - a n e w n am e adopted by the K och [R isley, 1891; S an yal, 1965]. Their traditional occu p a tio n s are fishin g and p lyin g o f boats, though som e o f them are n ow en gaged as agricultural labourers.
B lood sam p les from 85 unrelated Sadhu Poliya, 103 D esh i and 95 T iyor, i.e. a total o f 283 apparently h ealthy in d ivid u als b elon gin g to both sexes, were
collected in E D T A by finger pricks from M arch to June 1987. The haem oglobin types w ere screened by electrophoresis on starch gel and o n cellu lo se acetate strips in parallel alon g with k n ow n co n tro l sam ples.
The differentiation betw een Hb E a n d H b A 2 w as ver
ified by th e an alysis o f glob in ch ain s in cellu lo se ace
tate paper using T ris-E D T A -borate w ith citrate-urea buffer at p H 6.0.
The results of this analysis in the three populations (table 1) show ed a very high incidence o f Hb E allele am ong the Deshi and the Poliya. A significant deviation
Table 1. Distribution o f Hb E in three p o p u la tions o f the M alda district, W est B engal
Population H aem oglobin type H b E gene frequency
X2 value N A A A E EE
Poliya 85 17 52 16 0.494 5.86
D eshi 103 17 46 40 0.612 0.47
Tiyor 95 73 20 2 0.126 0.44
from the genetic equilibrium was observed' in the Poliya sample (p = 0.15) with ar.
excess o f heterozygotes. In the Deshi sam
ple a very high frequency of the E gene was observed, but in the Tiyor sample the E frequency was low.
T he th ree populations show significant differences in their distribution of Hbf frequencies ( p < 0.001). Even the Deshi and the Poliya, who have close ethnic affinities, differ significantly (p < 0.03).
W hen the present data are compared witl those from some M ongoloid populations o f A ssam and West Bengal (table 2), the D eshi p o p u latio n does not differ signifi
cantly from the Bodo-Kachari and Rabat o f A ssam b u t the Poliya show a signifi
cantly low er Hb E gene frequency that th a t o f the Bodo-K achari population. The D eshi po p u latio n shows significant!) h igher H b E frequencies than that of tie A hom . O n the other hand, the Tiyor do n o t d iffer significantly from the Rajbanshi a n d M ech populations of northern Wesi B engal, possibly due to their admixture w ith the neighbouring caste populations
T ab le 2. %2 values o f c om p arison betw een P oliya, D esh i a n d T iyor with som e M ongoloid populations ci A ssam and W est Bengal (in parentheses H b E gene freq uencies)
P opulation P resent study
P oliya (0.494)
D esh i (0.612)
T iyor (0.126)
B odo-K achari (0.645) 9.062 0.528 _ Deka etal., 1988
A hom (0.403) 3 .312 19.158 40.221 Deka et al., 1988
Rabah (0.535) 2.728 2.732 _ Das and Deka, 1980
R ajbanshi (0.230) - - 7.222 Deka et al., 1988
R ajbanshi (0.103) - - 0.402 Mukherjeeetal.,1®
M ech (0.173) - - 0.759 Mukherjeeetal., W
The Deshi population of the M alda d is
trict, though living far away from the high frequency area for Hb E in Assam [D as and Deka, 1985; Deka et al., 1988], e x h ib its one of the highest know n incidences o f the Hb E gene in the world along with the Bodo-Kachari [Deka et al., 1988], w ith whom it has ancestral affinities. T here is, however, no evidence of a recent a d m ix ture between these populations. T he re
sults of the present study do not co n fo rm to the hypothesis of adaptation to m ala ria [Flatz, 1967; K ruatrachue et al., 1969] in view of the following facts: (1) a signifi
cant increase in Hb E am ong the D eshi compared to the ancestral p o p u latio n o f i the Poliya, who have lived in a sim ilar en-
^ tironment for a long time; (2) the fre
quency distributions of Hb E in successive age groups do not indicate any change, a l
though a malaria control program m e has been operating successfully since the 1950s, and (3) the Tiyor show a very low frequency of Hb E despite their com m on ancestry and similar geographical e n v ir
onment. Ethnohistorical inform ation a n d cultural comparisons indicate th at b o th the Poliya (including the Deshi) a n d the Tiyor populations are offshoots o f the Koch tribe, which again is a branch o f the Bodo group of population spread over the plains of Assam and the northern p a rt o f West Bengal.
The genotypic frequencies in the a g ri
cultural Deshi population which displays the highest E gene incidence do not a p p e a r to deviate from genetic equilibrium . T here is no suggestion that the Hb E p o ly m o r
phism is transitional in the Deshi a n d there is no clear-cut indication o f any se
lection m echanism operating in this p o p u lation. The caste endogam y in a lim ited area and a fo u n d er effect might have led to a greater increase in the Hb E frequency am ong the D eshi p o p u lation th an in the Poliya, who are widely dispersed in the adjacent districts o f M alda and West D inajpur.
This work is partly supported by the award o f a Research A sso cia tesh ip o f U G C to M .K .D .
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Prof. B .N . M ukherjee
A n thropom etry and Human Genetics Unit In d ian Statistical Institute
203 B.T. R oad
C a lcu tta -7 0 0 035 (India)