Objective: Lactose intolerance is a common cause of gastrointestinal complaints in adolescents and young adults, often leading to unnecessary dietary restriction and reduced calcium intake. Although lactase non-persistence (LNP) is genetically determined, symptom expression varies considerably. Variants at the LCT/MCM6 locus, particularly rs4988235 and rs3754686, are frequently used in genetic testing; however, their clinical utility remains uncertain, especially in populations with a high prevalence of LNP, such as Türkiye.
Materials and Methods: In this cross-sectional study, 209 individuals aged 12–25 years were evaluated. Lactose-related symptoms were assessed using a validated questionnaire (a score ≥7 defined symptomatic individuals). Consumption of raw milk and fermented dairy products was recorded using a standardized frequency scale. Genotyping of rs4988235 and rs3754686 was performed using TaqMan real-time PCR. Associations between genotype, symptom status, age at symptom onset, and dietary patterns were statistically analyzed.
Results: Among the participants, 116 (55.5%) were symptomatic and 93 (44.5%) were asymptomatic. Symptomatic individuals were significantly older (p<0.001). The genotype distributions of rs4988235 and rs3754686 did not differ between the groups and were not associated with age at symptom onset. Dairy consumption patterns were not correlated with symptom severity, although fermented dairy intake was slightly higher among symptomatic individuals (p=0.046).
Conclusion: Common LCT variants do not predict clinical lactose intolerance in adolescents. Routine genetic screening appears unlikely to improve diagnosis or management. Symptom-based assessment and functional testing should remain central to care, supporting appropriate nutritional guidance and avoiding unnecessary dietary restriction.