Serum diamine oxidase activity is associated with lactose malabsorption phenotypic variation

Recently, an intermediate lactose intolerance (LI) phenotype based on the lactase gene (LCT) C/T_-13910 polymorphism was proposed. However, a multifactorial genesis of LI phenotypic variation including endogenous and exogenous factors cannot be ruled out. Therefore, this study was conducted to investigate a possible association between serum diamine oxidase (DAO) and LI phenotypes in individuals with lactose malabsorption (LM).

A total of 121 ambulatory patients with LM were included in this retrospective study. The lactose hydrogen breath test (LHBT) and serum DAO activity measurements were performed on the same day. A thorough anamnesis with respect to gastrointestinal symptoms was carried out at the initial consultation.

In total, 44 (36.4%) patients with a serum DAO activity <10U/mL showed higher H₂ levels after 60 (mean: 53.7±57.6 vs 34.5±31.7 parts per million [ppm], p=0.116), 90 (mean: 70.3±57.5 vs 52.7±41.4ppm, p=0.184) and 120min (mean: 98.9±72.5 vs 67.9±44.9ppm, p=0.012) during LHBT compared to 77 (63.6%) patients with a serum DAO activity ≥10U/mL. Individuals with a serum DAO activity <10U/mL tended to report gastrointestinal symptoms during the LHBT more often (p=0.091).

Our findings suggest that patients with LM and a serum DAO activity level<10U/mL had higher end-expiratory H₂ levels and tended to be more symptomatic during the LHBT compared to LM patients with DAO activity levels ≥10U/mL.