Journal of Applied Sciences & Environmental Management, Vol. 5, No. 1, June, 2001, pp. 79-81

A Comparison of Measured and Predicted Haemoglobin Genotype in a Nigerian Population in Bonny, Rivers State, Nigeria

*¹ NWAFOR    A;    ²BANIGO B.  M.

¹DEPARTMENT OF HUMAN PHYSIOLOGY  COLLEGE  OF  HEALTH SCIENCES  AND  ²DEPARTMENT   OF  MEDICAL    LABORATORY  SCIENCES   RIVERS  STATE  UNIVERSITY   OF  SCIENCE  AND  TECHNOLOGY,  PORT  HARCOURT
*Corresponding author

Code Number: ja01013

ABSTRACT

Cellulose acetate  electrophoresis    technique    has  been used  to estimate  haemoglobin  genotype  and    the  predicted  values   from the  estimate  in accordance with the population genetics  studies (Fleming  and Lehman 1982)  were  evaluated  in 850  subjects  (386 males  and  464  females)  selected  randomly  from  Bonny,  in Rivers  State,  Nigeria  of  ages between  3 and  77  years.  There was  significant differences  (P < 0.001)  between  the  measured  and  the  predicted  haemoglobin  genotype  values   suggesting  that  the  predicted  cannot be  substituted  for the   measured.  Two  further  haemoglobinopatheis,  HbSC  and  HbCC  were  predicted  to be  the  expected haemoglobin  genotype  of  newborn  into the  population  in the  next  decade  suggesting    that  the  incidence  of  abnormal  haemoglobin  in the  population  may  arise  from the  complex  interaction between the genetic constitution of the individual and some unidentified  environmental   factors. @ JASEM

The  percentage of person with one of  two types of haemoglobin genes – normal haemoglobin (HbAA) and abnormal  haemoglobin (sickle cell trait, HbAS,  sickle cell disease HbSS etc)  in a  community is an indication of Health  awareness  of  its  population.  Knowledge  and  care  of   whether  one is a  carrier  or   a  sickler  or  have  normal haemoglobin is therefore the  responsibility  of the  person  and  the  entire    community.           Available reports indicate important    differences in the distribution of  haemoglobin genotypes between Causcasians and  Africans  (Schnelder  et  al  1976,  Graham  1988,  Reid  and  Famodu,  1988,  Fleming  and  Lehman  1982).  The  most  prominent  feature is the prevalence  of  sickle  cell  trait/sickle  cell disease among Africans than Caucasians and this correlates with falciparium malaria parasite transmission theory (Allison, 1964).  There  is  however,  a  limited  number  of  information  of  studies  which  described  the  distribution  of  haemoglobin  genotypes  among Nigerian  population,  in particularly,  for a ethnic group in the swampy  environment  of the  Niger  Delta.  The   present report is, therefore, a study  designed  to find  out the  frequency  of  haemoglobin  genotype  in the  population  of  Bonny  ethnic  group  in the  Niger  Delta  from which  further  information  about  the  pattern  of distribution of normal and abnormal haemoglobin genotypes for  Nigerian  may  emerge. The    Hardy-Weinbery law  (Fleming  and   Lehman, 1982)  has  been  used  to predict  the  expected distribution of haemoglobin  genotype  of  newborn  into the  population   in the  next  decade. 

MATERIALS AND METHODS

Subjects were selected randomly and drawn among Bonny ethnic   groups located   on an island south  of  Nigeria  in the  Niger  Delta  at  the estuary  of the  Alantic  Ocean, and  a  former  seaport  during  the  slave  trade era. Currently, it  is  one  of the  largest  of  oil  exporting  terminals    in African  and  also  the  site  of  Nigeria  liquefied  Natural  Gas  Plants.  A  total  of  850  subjects  (386  males and  464  females)  with age  range  of  to 77 years  were  used  in the  determination of  haemoglobin  genotype.

Blood samples were collected by  venopucture    in  adults  and  by  finger  or  heel pricking  in  children  into  EDTA  anti-coagulant   bottles.  The  sickling  test  were  carried    out  at  a  slightly   acidic pH  of  6.8  (Fleming  and  Lehman, 1982)  to observe  the  presence  of  sickle  cells  under reduced  oxygen  tension.  The  electrophoretic  method    described  by  Fleming  and  Lehman  (1982)  and  Graham (1988)  was  used  as  a  confirmatory  test.   

For the study of the haemoglobin  electrophoresis, a small quantity of  haemolysate  of  venous  blood  from each  subject  was  placed on the  cellulose membrane and  carefully  introduced into the electrophoretic tank  containing  Tris-EDTA-Borate  suffer  89  as    described  by  Fleming and Lehman, (1982). The  electrophoresis  was  then  allowed  to  run  for  15  to  20  minutes  at  an  emf  of  160V. The results   were  read  immediately.  Hamolysates  from blood  samples  of  known  haemoglobin (BDH & Sigma, London) were run  as   controls.

RESULTS AND DISCUSSION         

The percentage of  the various  haemoglobin  genotypes  obtained  in  this  study  are  shown  in  Table  1.  Of  the  850  subjects  screened, 73%  are  HbAA, 22%  HbAS  and  4%  are  HbSS.  From  population  genetics  studies   (Fleming  and  Lehman, 1982), if  the  incidence  of sickle  cell  trait (HbAS)  is  known,  the  proportion of  infants  which   would  be  born  into  the  population  with each  haemoglobin genotype HbAA,  HbAS,  HbSS  etc  could    be  predicted.  When  the   percentage  genotype  of the  population  are  expressed  as  a  proportion  of  1.0 (Fleming  and  Lehman, 1982)  the  gene  frequencies  would  be  HbAA = 73,  HbAS = 72,  HbSS,  = 4,  HbAC = 1.

HbA = 73 + 11 + 0 + 0.5 = 84.5 
HbS = 0  + 11 + 4 + 0.0 =  15.0 
HbC = 0 + 0 + 0 + 0.5   =   0.5

Given  that  a,  s and  c  represent HbA, HbS and   HbC respectively  and  further  expressing  them  as  a  proportion  of  1.0,  gives  HbA = a = 0. 845, HbS = s = 0.15  and  HbC = c = 0.005. And   according  to Hardy-Weinbery law (Fleming and Lehman, 1982)  the  distribution  of  genotype  of  the  newborn  into the  population   in the  next  decade  would  be  obtained  as  follows:

(a + s + c)² = a² + 2as + s² + 2ac + 2sc + c²   = 1.0

Column 4 of  table 1 shows  the  predicted  values of the various haemoglobin  genotypes  and showed a  further two  haemoglobinopathies  being introduced  into the  population as a  result of  gene  recombination.  The predicted HbAS  values  was significantly higher  than  the  measured  value.  On the  other hand,  the  measured  valued  for  HbSS was  significantly   higher  than  the    predicted   value  (P > 0.001).

Table 2 shows the frequency of  haemoglobin  genotype in males  and females. The  percentage  of  females  that  are  HbAA,  HbAS  and  HbSS  are  more    than the corresponding  percentage of  males. This  represents differences of  44.3%, 17.0%  and  26.5%  respectively  (P>0.001). The  ratio  of  HbAA to HbAS  was  3:1,  HbAA  to  HbSS, 20:1  AND  HbAA  to HbAC 78:1.  The   ratio  of  HbAS  to  HbSS  was  6:1, and  HbAS  to HbAC 24:1  and  the  ratio   of   HbSS to  HbAC  was  4:1.

From our  study, the predicted values  of  the  abnormal  haemoglobin  genotype  sickle  cell  anaemia (HbSS)  was  less  than  the    measured  values  with  a  mean  difference  of  121.5%  and  both  measured  and  the  predicted    values  were  lower  than  the  range   30  to  46%  generally  reported  for  Africans  (Allison  1964, Richard 1975,  Lewis 1970).  In  the   U.S.A.  9%  of  the  black population  are   HbSS (Richard, 1975).  A   possible  explanation   for   this  significant observed  low incidence  in  HbSS might  be  attributed to environmental  factors which include: Improved socio-economic conditions, better nutrition, blood type compatibility, absence and / or presence  of  malaria  parasite  infection,  all of  which  tend  to  influence the  importance  that  a  person   places  on his  health,  and  the  degree  of  care  that  he  may  seek  to protect   it.  Alternatively,  the    lower  the  socio-economic   and  the  educational  level  and the difficulty of seeking medical  advice  and  care  of  people  of  rural   dwellers,  to say,  might  influence  the  incidence  of  abnormal  haemoglobin  in  the  population.  Furthermore there was significant differences (P < 001) between the  predicted  and  the measured    haemoglobin  genotype.  This  might   suggest  that  the  predicted  values might be are over / or under simplication of   the result. However, two further haemoglobinopethis HbSC and HbCC were predicted using the  population  genetic  equation of  (Fleming  and  Lehman 1982)  to be  the  expected haemoglobin  genotype  of  new  born  into  the    population  in the  next decade.  This   might    suggest  that  the   incidence  of  the  abnormal  haemoglobin  in the  population  may arise  from  a  complex interaction  between  the  genetic   constitution  of  the  individual and some unidentified  environmental  factors.

The  observed   high   incidence  of  HbAA  and  HbAS in the population, though  the    frequency  of  HbAA  being  significantly  higher  than  that for HbAS, is in  agreement with previous reports  that  the  normal  haemoglobin  (HbAA),  range  from 55  to 75%  (Fleming  and Lehman, 1982), and  the  sickle  cell  trait  (HbAS)  20  to  30%  in  Nigeria (Reid  and  Famodu, 1988)  and  20 to  40%  in Africa (Fleming  and  Lehman, 1982).  The    present   study  has for the first  time also  established  the ratio  for  each  of the  haemoglobin  genotypes.

The study  also  showed  percentage  distribution  of  persons  for  haemoglobin  genotype  by  sex  and found that there were significance  difference  between  males  and  females  in  the  distribution  of  HbAA, HbAS and HbSS (P<0.001). The difference might be  a  reflection  that  females  generally  are    known  to  be  home  bound  than  males,  but  the  main reason  for  this  disparity   between  the  number  of  males  and  females examined  was  that  men  are  less  likely  to be at  home  during  the  day  time  and  perhaps  another  reason  may  simply  be  increased  frequency  of  clinic  attendance  by  females  compared  to males.

It  is  note  worthy  to highlight  problems   encountered  and this was the belief and  attitude  of  the  people   towards  the use  of  blood.    It  was  difficult to  convince  the  people  that  their  blood  was  not  being used for    ritual  purposes  rather  for the    determination of the  state  of  their  well  being.  Our  experience  suggests  that  mass  literacy  campaign   was  required    to educate  people  on the  need  to donate  blood  as  well have  their  blood  examined  because  ignorance  of the  importance  of this  study (as  well as proper matching, HIV/AIDS) could  lead  to genetic incompatibility in marriages involving    individuals carrying  the sickle  cell  trait  an / or  suffering from sickle cell anaemia and  consequently a  congential abnormal  offsprings.

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