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Objectives: Our study aims to determine the age of onset of adult-type hypolactasia in Sardinians, and to establish the age at which genotyping of the C/T-13910 variant can be used reliably in the diagnosis of lactose malabsorption., Patients and Methods: A lactose breath hydrogen test was given to 383 randomly selected patients, from 3 to 19 years old., Results: The C/C-13910 genotype was found in 90% of patients; the frequency of the positive lactose breath hydrogen test increased with age and reached a prevalence of 85% at 9 years., Conclusions: In Sardinians, adult-type hypolactasia becomes phenotypically evident in all individuals older than 9 years, suggesting that this should be considered the minimum age at which the genetic test for lactase nonpersistence should be applied.

Objective: Recently, the C/T-13910 polymorphism on chromosome 2q21 in North-European populations has been found completely associated with lactase activity and its genetic typing proposed as first-stage screening test for adult hypolactasia. However, the C/T-13910 variant in some sub-Saharan African groups is not a predictor of lactase persistence. In this work, we wanted to verify if in the Mediterranean island of Sardinia, located in Southern Europe, the C/T-13910 polymorphism may be useful or not for the diagnosis of adult type hypolactasia., Design: Validation study of a genetic testing for adult type hypolactasia in Sardinians., Setting: Brotzu Hospital and Microcitemico Hospital, Cagliari, Italy., Subjects: The sample consisted in 84 Sardinian individuals (63 women and 21 men; range 20-73 years) selected from a group of 832 patients., Methods: Genetic testing was compared to an improved test obtained by a combination of different breath hydrogen tests and clinical assessment., Results: We found that all 49 individuals with lactose malabsorption, demonstrated by a combination of different breath hydrogen tests and clinical assessment, carried the C/C-13910 genotype associated with lactase non-persistence, 23 individuals with lactose normal absorption carried the C/T-13910 genotype associated with lactase persistence and only one person with the above phenotype showed a discordant C/C-13910 genotype. The genetic testing showed very high sensitivity, specificity, positive and negative predictive values of 100, 95.8, 98 and 100%, respectively., Conclusions: Sardinians, unlike some ethnic groups in sub-Saharan Africa, show the same genetic association of hypolactasia with the C/T-13910 variant as other North-European populations. The genetic testing for the C/T-13910 variant may contribute to improving the diagnosis of adult type hypolactasia.