In 2005, about 20 percent (82,600 million gallons per day (Mgal/d)) of total national water withdrawals (about 410,000 Mgal/d) came from groundwater sources. (All 2010 water use information is from the report Estimated use of water in the United States in 2010.) Very little saline groundwater was used in 2005.
The MTHFR nucleotide at position 677 in the gene has two possibilities: C (cytosine) or T (thymine). C at position 677 (leading to an alanine at amino acid 222) is the normal allele. The 677T allele (leading to a valine substitution at amino acid 222) encodes a thermolabile enzyme with reduced activity.
MTHFR mutations are common. The mutations can be âheterozygousâ meaning they occur only on one strand or âalleleâ of the chromosome, or they can be âhomozygousâ, occurring on both alleles. The frequency of a heterozygous C677T mutation is common, occurring in about 35% of the population.n abnormal change in gene structure, called a mutation, of the MTHFR gene can cause a disruption of the MTHFR enzymeâs normal function of breaking down homocysteine.