Recently, UC Berkeley announced their “Bring Your Genes to Cal” Project, offering personalized genetic testing for all incoming freshmen.
The program allowed incoming students, on a voluntary and anonymous basis, to submit DNA samples, with the promise that they would receive their personal results of tests for three common genetic variants.
The program had IRB approval, so concerns about human subjects protection had apparently been satisfied. From the project FAQ:
We decided to invite you to participate in this voluntary limited genetic test in the hope that it would provoke you to think more deeply about the rapidly increasing role of DNA analysis in decisions involving your health and medical care. Also, you will get a sense of the types of information that analysis of your genome can reveal.
John Hawks was not impressed. The genes in question code for metabolic enzymes used to break down lactose (milk sugar), alcohol, and folic acid. Sounds benign enough – three genes related to health and nutrition.
Great plan! I’m sure that your lactose intolerant students will shocked to discover that they’re lactose intolerant! OMG! That explains the milkshakes! Likewise, I’m sure that the health impacts of alcohol consumption will get your 18-year-old freshmen to booze less on the weekends! And that folate metabolism test, well, that will get them used to supplements, won’t it?
From an anthropological genetics perspective, however, testing for these genes could have unintended consequences, because the frequencies of these genes vary by population.
For example, lactose intolerance results from low activity of lactase, an enzyme that is active in human infants, but is silenced in most human adults. Some populations which have a long history of dairy consumption, however, maintain activity of the lactase gene throughout adulthood.
From the map, most adults in East Asia, Central and South America have silenced lactase genes.
The second gene codes for alcohol dehydrogenase (ALDH2), an enzyme which converts alcohol to acetaldehyde. Individuals who have the ALDH2*2 allele have the less active form of the enzyme, and thus metabolize alcohol more slowly. The chart below shows changes in blood acetaldehyde levels over time after consumption of alcohol or a placebo. There is a significant difference between acetaldehyde elimination in individuals who are homozygous for the ALDH2*1 allele versus those that have one copy of the ALDH2*2 allele.
The low activity allele is much more common among Asian populations.
…[H]alf of certain Asians, including Chinese, Japanese, and Korean persons, have a deficiency of the low-Km mitochondrial aldehyde dehydrogenase (ALDH2) isoenzyme….A deficiency of ALDH2 results from inheritance of the mutant ALDH2*2 allele, a dominant mutation that exerts its effect both by reducing enzyme activity and increasing the turnover of this activity. After ingestion of alcohol, the faces of Asians with one or both alleles of ALDH2*2 become visibly flushed. Asians who are homozygous for ALDH2*1 generally lack visible alcohol-induced flushing or experience only a mild flush response (Wall et al. 1997:376).
The third gene codes for methylenetetrahydrofolate reductase (MTHFR), an enzyme which helps break down folic acid. A mutation at a single base in the MTHFR gene results in reduced enzyme activity, and can cause elevated levels of the potentially toxic amino acid homocysteine, particularly in populations with low dietary folate intake. As with the previous two genes, MTHFR frequencies show worldwide variation. A comparative study found frequencies of the reduced activity allele (677T) highest in Mexican populations, while populations with the lowest frequencies are found in Africa.
The issue with these three gene is not that they are uninformative, but that they may reveal too much.The project FAQ states:
It is indirectly possible to get some information about ethnoracial identity, since at least one of the genes involved (for lactose intolerance) is distributed differently across ethnoracial groups.
All of these genes provide indirect information about ancestry, not just “specific genes that are linked to particular metabolic conditions.” Suppose a student whose parents are of European ancestry discovers from the “Bring Your Genes to Cal” project that they have the ALDH2*2 allele. Not only does it mean that they will have an adverse physiological response to consuming alcohol, but that the student’s ancestry could be called into question. Potentially, these tests could reveal more information than either the student or the school are prepared for.
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Guéant-Rodriguez RM, Guéant JL, Debard R, Thirion S, Hong LX, Bronowicki JP, Namour F, Chabi NW, Sanni A, Anello G, Bosco P, Romano C, Amouzou E, Arrieta HR, Sánchez BE, Romano A, Herbeth B, Guilland JC, & Mutchinick OM (2006). Prevalence of methylenetetrahydrofolate reductase 677T and 1298C alleles and folate status: a comparative study in Mexican, West African, and European populations. The American journal of clinical nutrition, 83 (3), 701-7 PMID: 16522920
Wall TL, Peterson CM, Peterson KP, Johnson ML, Thomasson HR, Cole M, & Ehlers CL (1997). Alcohol metabolism in Asian-American men with genetic polymorphisms of aldehyde dehydrogenase. Annals of internal medicine, 127 (5), 376-9 PMID: 9273829
