Serum diamine oxidase activity is associated with lactose malabsorption phenotypic variation.

Objectives 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). Design and methods 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. Results In total, 44 (36.4%) patients with a serum DAO activity < 10 U/mL showed higher H 2 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 ± 41.4 ppm, p = 0.184) and 120 min (mean: 98.9 ± 72.5 vs 67.9 ± 44.9 ppm, p = 0.012) during LHBT compared to 77 (63.6%) patients with a serum DAO activity ≥ 10 U/mL. Individuals with a serum DAO activity < 10 U/mL tended to report gastrointestinal symptoms during the LHBT more often ( p = 0.091). Conclusions Our findings suggest that patients with LM and a serum DAO activity level < 10 U/mL had higher end-expiratory H 2 levels and tended to be more symptomatic during the LHBT compared to LM patients with DAO activity levels ≥ 10 U/mL. [ABSTRACT FROM AUTHOR]