Doris Huerta

Possible positive selection for an arsenic-protective haplotype in humans

Background: Arsenic in drinking water causes severe health effects. Indigenous people in the South American Andes have likely lived with arsenic-contaminated drinking water for thousands of years. Inhabitants of San Antonio de los Cobres (SAC) in the Argentinean highlands generally carry an AS3MT (the major arsenic-metabolizing gene) haplotype associated with reduced health risks due to rapid arsenic excretion and lower urinary fraction of the monomethylated metabolite. Objectives: We hypothesized an adaptation to high-arsenic living conditions via a possible positive selection for protective AS3MT variants and compared AS3MT haplotype frequencies among different indigenous groups. Methods: Indigenous groups we evaluated were a) inhabitants of SAC and villages near Salta in northern Argentina (n = 346), b) three Native American populations from the Human Genome Diversity Project (HGDP; n = 25), and c) five Peruvian populations (n = 97). The last two groups have presumably lower historical exposure to arsenic. Results: We found a significantly higher frequency of the protective AS3MT haplotype in the SAC population (68.7%) compared with the HGDP (14.3%, p < 0.001, Fisher exact test) and Peruvian (50.5%, p < 0.001) populations. Genome-wide microsatellite (n = 671) analysis showed no detectable level of population structure between SAC and Peruvian populations (measure of population differentiation FST = 0.006) and low levels of structure between SAC and HGDP populations (FST < 0.055 for all pairs of populations compared). Conclusions: Because population stratification seems unlikely to explain the differences in AS3MT haplotype frequencies, our data raise the possibility that, during a few thousand years, natural selection for tolerance to the environmental stressor arsenic may have increased the frequency of protective variants of AS3MT. Further studies are needed to investigate this hypothesis.

POLIMORFISMO GENÉTICO DE LA APOLIPOPROTEÍNA E EN UNA POBLACIÓN PERUANA

Objetivos. Determinar las frecuencias genotipicas y alelicas del gen APOE en una muestra poblacional peruana. Materiales y metodos. Estudio transversal analitico en 189 trabajadores voluntarios, aparentemente sanos, del Instituto Nacional de Ciencias Neurologicas en Lima, Peru, divididos en cinco grupos segun departamento de origen y ascendencia en dos generaciones. El ADN genomico fue amplificado mediante PCR-RFLP. Se realizo la deteccion de los fragmentos resultantes por electroforesis en gel de poliacrilamida al 12 %. Resultados. El alelo e3 es el mas frecuente en todos los grupos (93,9 %), con bajas frecuencias de los alelos e4 (5 %) y e2 (1,1 %). El anαlisis de heterocigosidad (H) en cada grupo muestra una diversidad intermedia entre 10 y 20 %. Las diversidades genιticas poblacional (Ht) e intrapoblacional (Hs), son 14,4 y 14,3 % respectivamente, sugiriendo proximidad genetica entre los grupos estudiados para el polimorfismo ApoE. Conclusiones. Las frecuencias alelicas del gen ApoE encontradas muestra que el alelo e3 tiene una de las frecuencias mas altas y, el alelo e4, una de las mas bajas respecto a otros grupos poblacionales del mundo, con posibles implicancias en el riesgo para enfermedades neurologicas, cardiovasculares y otras en nuestro pais.

Chaos control: The problem of a bouncing ball revisited

The problem of a body bouncing on a periodically oscillating surface is revisited to demonstrate chaos control. When the bouncing body is magnetic, it is possible to modify its behavior by adding a magnetic driving force. The mechanism of chaos control may be understood by means of a mechanical analysis which shows that the main result of applying the driving force is to shift the bifurcation diagram in such a way that chaotic behavior is replaced by periodic behavior and vice versa. A simple experiment is presented, along with a numerical simulation, that provides insight into chaos control.