Summaries of selected genetics, genomics, and family history-related studies using NHANES data, 2001-2009

To assess how common asthma is in the U.S. and the association between family history of asthma and having asthma.

Researchers analyzed National Health and Nutrition Examination Survey data from 1999 to 2004 for 15,008 adults aged 20 years or older, excluding people with a history of respiratory problems.

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• About two out of 100 (or 2.3%) people had a high risk for asthma based on their family history, thirteen out of 100 (or 13.0%) had a moderate risk; and most people, about 85 out of 100 (or 84.7%), were at average risk
• About 38 out of 100 (or 37.6%) people in the high familial risk category had asthma, about 20 out of 100 (or 20.4%) people in the moderate familial risk category had asthma, and about 9 out of 100 (or 9.4%) people in the average familial risk category had asthma
• Among all risk factors evaluated, family history had the strongest association with developing asthma at any age; risk factors included age, sex, race/ethnicity, income, body mass index, smoking status, household smoking exposure and physical activity
• People with a moderate familial risk of asthma have a 2.4 times increased risk of lifetime asthma and whereas the risk among people with a high familial risk is 4.8 times higher, compared to people at average risk, after adjusting for other factors
• The findings showed that having a family history of asthma increases the risk for developing the disease, and that knowing family history for asthma can help identify people at highest risk

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To estimate how common (or prevalent) variants of folate-related genes are in the U.S. population, and to examine how these genes affect serum folate and homocysteine concentrations in the blood.

Abnormalities in the metabolism of folate and homocysteine are associated with disease and conditions (such as neural tube defects, dementia, cognitive function, osteoporosis, cancer, cardiovascular disease and stroke) that contribute significantly to morbidity and mortality among children and adults.

Researchers used the DNA samples from 6,793 participants in NHANES III (collected from 1991 to 1994) for this study. They genotyped these samples for four variants in genes coding for folate pathway enzymes: 5,10-methylenetetrahydrofolate reductase (MTHFR) C677T and A1298C, methionine synthase reductase (MTRR) A66G, and cystathionine-beta-synthase (CBS) 844ins68.

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• Across all race/ethnicity groups, people with the MTHFR 677 TTgenotype had a 22.1% lower serum folate and a 25.7% higher homocysteine concentration than people with the MTHFR 677 CC genotype
• Among people taking moderate daily amounts of folic acid, MTHFR 677 genotype had a smaller effect on homocysteine concentration Compared to people not taking folic acid supplements
• This study provides a better understanding of how genetic variants contribute to serum folate and homocysteine concentrations, and how the genetic effects might be modified by folic acid intakes
• Among race/ethnic groups, the prevalence of HFE mutations varied

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To estimate how common (or prevalent) two mutations of the Hemochromatosis (HFE) gene, which is crucial for iron metabolism, are in the U.S. population.

Researchers used the DNA samples from 5,171 participants in NHANES III (collected from 1992 to 1994) for this study.

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Learn about the HFE gene.

• This study provides an estimate of the percentage of people in the U.S. with two mutations that account for most cases of hereditary hemochromatosis among individuals of European descent
• In the total U.S. population:
  • 5.4% of people had at least one copy of the C282Y mutation
  • 13.5% of people had at least one copy of the H63D mutation
• In the total U.S. population:
  • 8.33% of people are heterozygous for C282Y (C282Y/wild type), while 0.26% of people are homozygous (C282Y/ C282Y)
  • 21.36% of people are heterozygous for H63D (H63D/wild type), while 1.89% of people are homozygous (H63D/ H63D)
  • 1.97% of people are heterozygous for both mutations (C282Y/H63D)
• Among race/ethnic groups, the prevalence of HFE mutations varied
  • C282Y heterozygosity (C282Y/wild type) was highest among non-Hispanic whites (9.54%), followed by Mexican Americans (2.75%), and non-Hispanic blacks (2.33%)
  • The prevalence of H63D heterozygosity (H63D/wild type) was also highest among non-Hispanic whites (23.55%), followed by Mexican-Americans (19.70%), and non-Hispanic blacks (5.55%)
• This study may inform decisions about screening for these HFE mutations in different U.S. subpopulations

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To examine the association between hereditary hemachromotosis (HFE) genotypes and transferrin saturation (an indicator of circulating iron) in the U.S. population by race and ethnic group, age, and sex.

Researchers used the DNA samples from 5,171 participants in NHANES III (collected from 1992 to 1994) for this study.

Learn about hemochromatosis.

Learn about the HFE gene.

• 77% of men and 51.9% of women homozygous for the C282Y gene mutation had high transferrin saturation
• People aged 50 years or older who are homozygous for the H63D mutation had a stronger association with high transferrin saturation than younger persons (aged 12-49 years)
• Among Mexican Americans, H63D heterozygosity was associated with high transferrin saturation
• Among race/ethnic groups, the prevalence of HFE mutations varied
• This study provides a better understanding of the genetic contribution to iron overload and shows that the association between HFE genotype and high transferrin saturation differs by sex, age, and race/ethnic group

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To assess how common osteoporosis is in the U.S., the association between family history of osteoporosis and having osteoporosis, and the likelihood that women at high familial risk of osteoporosis report preventive behaviors.

Researchers analyzed National Health and Nutrition Examination Survey data from 1999 to 2004 for 8,073 women aged 20 years or older

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• Eight out of 100 (or 7.94%) adult women reported being diagnosed with osteoporosis
• Twenty out of 100 (or 19.8%) adult women said that they have a family history of osteoporosis; family history was significantly and independently associated with osteoporosis
• Women with a family history of osteoporosis were:
  • 2.4 times more likely to have osteoporosis than women without such history
  • 8.5 times more likely to have osteoporosis when two or more relatives were affected, for women aged 35 years or older
  • more likely to report preventive behavior such as, taking calcium supplements, vitamin D, or both; increased physical activity; and estrogen use
• This study showed that people with a family history of osteoporosis have an increased risk for developing the disease, particularly for women aged 35 and older. Along with other risk factors, family history is an important and independent risk factor for osteoporosis

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