The therapeutic value of visual-perceptual training and its effect on scholastic achievement.

colonial times_ Atthough there are great inter-tribal variations in SGT, the HbS gene has been reported from nearly all subSaharan African countries including the neighbouring ocean islands, except the mainly Cushite Ethiopia and Somalia.io'o Recent studies have shown the gene to be present in tribes in which it was originally found to be absent 30 years ago." This type of change in the HbS spread is allributalble to increased and improved inter-ethnic communication and resultant intermarriage.12 Although SCT and SCD have been reported in some Mediterranean white populations,lo.'3 the current HbS prevalence is unknown in South African whites. The HbS prevalence in the non-white South African population ranges from 0% to 5%...·10,1....1S South Africa is becoming a forceful democratic muttiracial nation. As has been seen in Kenya12 and e1sewhere,I.1.1!>-ll increased and improVed inter-ethnic relationships resulting from such major changes may also resutt in an increase in intermarriage. This may lead to the introduction of lI1e HbS gene into tribes or races that did not have it. Although the impact of such changes will remain limITed for a considerable length of time before manifesta~onof frank SGD, we should be aware of the trend, not only in South Africa but also in oll1er parts of Africa where HbS was known to be absent in some ethnic groups. When possible within the framework of various national health priorities, fresh surveys are recommended for reassessment of HbS frequency and the prevalence of SGD in various African countries.