The study, published in PLoS Pathogens, explains how two enzymes enable the cell's surface to remodel itself in order to thwart the immune system of carrier tsetse flies.

African trypanosomiasis has long been endemic in regions of Sub-Saharan Africa. The fatal parasitic disease is known to largely affect humans and livestock. The disease currently affects roughly 60 million people in 36 African nations. Bloodstream trypanosomes thwart their host's immune response by periodically switching their major surface protein, the variant surface glycoprotein (VSG). In this study, researchers looked at how trypanosomes shed their VSG to survive within the tsetse fly's midgut. By experimenting with enzyme gene deletion, Grandgenett et al. could test the parasite's survival rate.

This study addresses a key issue in the pathogenesis of African Trypanosomiasis: how the surface coat of the parasite is "shed" to facilitate immune evasion. Much previous work has been aimed at addressing this question and this work is the clearest identification of molecules involved in this process.

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Because these tests trace only one bloodline, however, they exclude most ancestors. Moreover, they cannot pinpoint where these ancestors lived. "Each test examines less that one percent of the test-taker's DNA and sheds light on only one ancestor each generation," the study says.

A third option, known as AncestryByDNA, or admixture testing, is more promising in that it examines non-sex chromosomes inherited from both parents, chromosomes that contain DNA segments from all ancestors. To a limited extent, this test can track the geographical movements of ancestors by examining single nucleotide polymorphisms (SNPs), some of which influence such traits as skin color and resistance to regional diseases. That said, the same SNPs may be found among several populations around the world, and thus can produce false leads.

"Worldwide patterns of human genetic diversity are weakly correlated with racial and ethnic categories because both are partially correlated with geography," the study says.

Moreover, the success of genetic matching depends largely on the number of samples in a company's database. "Even databases with 10,000 to 20,000 samples may fail to capture the full array of human genetic diversity in a particular population or region," the study says.

Furthermore, the study says, AncestryByDNA tests rely on "ancestry informative markers" (AIMs), which show genetic differences between what are assumed to be four biologically distinct populations: Africans, Europeans, East Asians and Native Americans.

But "the AIMs that characterize 'Africans,' for example, were chosen on the basis of a sample of West Africans. Dark-skinned East Africans might be omitted from the AIMS reference panel of 'Africans' because they exhibit different gene variants," the study points out.

The AncestryByDNA test also reads certain markers found in people from the Middle East, India and the Mediterranean region to be diagnostic of Native American ancestry, for which there is no historical, archeological or genetic evidence, according to the study.

Indeed, the article gives very little credence to these tests, which it concludes "cannot pinpoint the place of origin or social affiliation of even one ancestor with exact certainty."

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