DAO His645Asp - The Third Piece of the DAO Puzzle
The His645Asp | Histidine to aspartic acid at position 645 variant (rs1049793) is the third major functional variant in the
AOC1 gene encoding diamine oxidase. This missense mutation replaces histidine with
aspartic acid at position 645, which sits near the enzyme's catalytic domain.
The Mechanism
Position 645 is in a region of the DAO protein that contributes to substrate
binding and catalytic turnover. The aspartic acid substitution | Histidine is positively charged at physiological pH while aspartic acid is negatively charged, dramatically changing local electrostatics (G allele) alters
the local charge distribution, potentially affecting how efficiently the enzyme
captures and degrades histamine molecules. Like the other DAO structural variants,
this change reduces the enzyme's overall effectiveness. Ayuso et al. | Ayuso P et al. Genetic variability of human diamine oxidase. Pharmacogenet Genomics, 2007
showed that heterozygous carriers had 34% reduced DAO activity and homozygous carriers
had 49% reduced activity compared to non-carriers.
Combined DAO Status
The three major AOC1 variants (rs2052129, rs10156191, and rs1049793) together
determine your overall DAO capacity. Research has demonstrated that these variants
are partially independent - you can carry risk alleles at one position but not
others. This means your total DAO function is best assessed by looking at all
three variants together, rather than any single one in isolation.
Population Variation
This variant shows substantial population differences. The G allele frequency is
approximately 30% in Europeans but reaches 49-54% in East Asian, South Asian, and
African populations. This means reduced DAO activity at this position is more
common in non-European populations.
Practical Guidance
The dietary strategies for managing reduced DAO function are consistent regardless
of which specific variant is responsible: minimize high-histamine foods, prioritize
freshness, and consider DAO supplementation with meals when consuming foods that
are known histamine triggers. Importantly, histamine intolerance symptoms can wax
and wane depending on your total histamine load | Your histamine load is the sum of all histamine from diet, gut bacteria, allergic reactions, and internal production at any given time from food, environment, stress,
and hormonal fluctuations.
All genotypes
Normal DAO at this position
Normal DAO enzyme at this structural position. About 50% of Europeans have this genotype.
One DAO structural variant
You carry one variant that may reduce DAO activity by approximately 34%. About 40% of Europeans share this genotype.
Reduced DAO activity at this position
Two variants reducing DAO activity at this position by approximately 49%. About 10% of Europeans have this genotype, though it is more common in East Asian and African populations.