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Examination of lactose intolerance by DNA sequencing
JAVŮRKOVÁ, Petra
Lactose intolerance is one of the most common food intolerances. It is caused by decrease of lactase enzyme in the small intestine epithelium, which leads to insufficient lactose metabolism and its accumulation. Lactase loss may be congenital, primary or secondary. The first two types are genetically conditioned. Large interest of this issue in the last few years has led to identification of single nucleotide polymorphisms (SNPs) which are associated with lactose intolerance. Within European population, two most significant polymorphisms keep occurring: C/T-13910 and G/A-22018. Owing to the fact, these are practically the only ones that are examined in European population. Each SNP is identified by NCBI and has its own identification number (ID), by which it can be identified and traced in gene databases, professional publications, etc. Polymorphism C/T-13910 is coded as rs4988235 and G/A-22018 as rs182549. While the impact of homozygous and heterozygous genotypes in both polymorphisms on individuals is widely known, there is very little information about the combined genotype in the professional literature. In the practical part of the bachelor thesis I focused beside other analysis on individuals who are homozygous only in one of the polymorphisms. All patients were firstly selected based on preliminary results obtained by PCR-RFLP method and then re-examined by another independent method, known as sequencing. The final compilation consisted of 20 samples with different genotypes, in half of which combined genotypes were presented. Based on comparison of sequencing results and PCR-RFLP results, some discrepancies were found in 20 % of presented samples. After comparing both mentioned diagnostic approaches in the discussion, I have evaluated the sequencing method more reliable. On the other hand, sequencing method is more demanding in terms of laboratory equipment and is also more expensive than the PCR-RFLP method. For this reason, sequencing is not used for routine diagnosis of lactose intolerance.
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