Genetic protection against AIDS
Some people do not become infected with the HI virus despite frequent contact with infected people. The reason is a mutation in the CCR5 receptor, which protects against the disease as soon as it is homozygous, i.e. in both chromosomes of the affected person. French researchers have now investigated the effect of a mutation occurring in only one chromosome in children. In 1996, scientists discovered that a specific mutation (delta 32) in the CCR5 receptor protects people from infection with AIDS if it is homozygous. If the mutation is limited to one of the chromosomes (heterozygous), those affected can be infected by HIV. So far there are no clear results on how exactly a heterozygous presence of the mutation affects the progression of the disease.
The examinations are difficult because the exact date of infection cannot usually be determined and multiple infections cannot be ruled out. Scientists from INSERM (the French National Institute for He alth and Medical Research) and the Ho^pital Bicetre report in the Journal of the American Medical Association (January 28 issue) a study that took these issues into account. The French researchers studied children who were infected by their mother as a fetus. In this way, the time of infection is known and other routes of infection can be ruled out.
512 children of mothers of European descent who were infected with HIV-1 were examined. Infected (n=276) and uninfected children (n=236) were screened for the delta 32 mutation. The proportion of heterozygotes was similar in both groups. This indicated that, as in adults, children heterozygous for the delta 32 mutation are not protected against HIV-1 infection.
Of the 152 infected children, 126 children had no mutation, while the remaining 26 were heterozygous. The progression of the disease was then compared in all those infected: severe clinical symptoms and the onset of a severe immune deficiency (measured by the drop in the number of CD4+ cells in the blood) occurred much later in heterozygous children.
These findings provide important arguments in the debate about the effect of the delta 32 mutation. Determining the genotype can also provide prognostic information for the children of HIV-1 infected mothers.
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