The more recent study did statistical tests to demonstrate that the samples were moderately homogeneous. In both cases, the effect sizes were small, but the samples were not corrected for population stratification. 9 The same report also examined data from 1,862 Caucasian American women, and found that light-eyed women reported significantly more alcohol than dark-eyed women. A study of 10,860 Caucasian adult male inmates in the Georgia state prison system found that 42% of light-eyed inmates had alcohol abuse problems while the fraction of dark-eyed inmates with alcohol abuse problems was 38%. This is not the first association to be made between eye color and alcohol use. 8 What the study found was a higher statistical correlation between lighter eye color and alcoholism than between brown eye color and alcoholism, and the correlation was markedly higher for blue eyes. Is Pale Eye Color Associated with Elevated Risk of Alcoholism?Ī recently published study looked at over 1,200 people who were either diagnosed alcoholics or were similar in age, sex, and ethnic background (European descent) but were not alcoholics although they did occasionally consume alcohol. G-protein coupled metabotropic glutamate receptor Succinate dehydrogenase complex assembly factor Neuronal nicotinic acetylcholine receptor Rather, as with other complex traits such as BMI or cancer risk, risk is the result of the cumulative effect of multiple variants with modest individual impact. The individual association of each of these genes with the risk of alcohol dependency is relatively weak. Many of these genes encode proteins important for neurotransmitter signaling, receptors activated by drugs and enzymes required for alcohol metabolism (See Table 1). Genome-wide association studies and candidate gene analyses have identified many gene variants significantly associated with alcohol dependency. A 2006 Centers of Disease Control study estimated the cost of excessive alcohol consumption to be $223.5 billion, reflecting a toll on workplace productivity, health care expense, criminal justice expenses and from motor vehicle crashes ( ).Īlcohol use disorder has an estimated heritability of 40–60%, 3 – 6 with complex underlying genetics. Excessive alcohol consumption kills about 88,000 people in the U.S. 2 In 2012, approximately 11.2 million adult men, 5.7 million adult women and 855,000 persons aged 12– 17 had AUD in the U.S. In 2013, alcohol dependency was formally reclassified together with alcohol abuse as “alcohol use disorder (AUD).”Įxcessive alcohol use is the third leading modifiable cause of death in the United States. So the parts of the world where descendants of that founder individual are most common have the highest frequency of blue eyes where those descendants are rare, darker eye colors are the dominant eye color.Ĭontinued use despite knowledge of alcohol-related physical or psychological harm. 1 The evidence suggests that all people with blue eyes carry this same variant. About 6,000–10,000 years ago, probably in the area of the Black Sea, a single individual was born with a mutation that programs reduced OCA2 gene expression and blue eyes. As our ancestors migrated out of Africa, some found their way into Europe. The current genetic evidence suggests that the first humans had brown eyes. However, as many as seven other genes can impact melanin deposition, resulting in shades of blue and green and explaining why two blue-eyed parents can have green-eyed children.Įye colors other than brown only occur in individuals of European descent. 1 The more OCA2 activity in the iris melanocytes, the darker the eye color. The OCA2 gene on human chromosome 15 has a major impact on eye color by producing a protein that controls melanin formation and processing. Most Americans are taught that eye color is a single-gene trait - that a brown-eye gene variant is dominant over the blue-eye variant. Right: melanosomes (colored ovals) increase in number and melanin content in (top) blue eye melanocytes, (middle) hazel eye melanocytes and (bottom) brown melanocytes. Left : representations of the pupil (black) and surrounding iris color in (top) blue eyes, (middle) hazel eyes and (bottom) brown eyes. Eye color is determined by the number and melanin content of melanosomes within the melanocytes of the anterior iris stroma.
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