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Practical Applications
Pleiotropy is instrumental in the study of several genes and their expression. By researching relationships between multiple phenotypic traits and a single gene, scientists can glean a better understanding of the frequency and other properties of this phenomenon.

In Research
Geneticists’ primary research goals are to link pleiotropic genes to each of their phenotypic traits and to determine any relationships between which genes in a genome are pleiotropic and why. To that end, the most frequently used mechanism is reverse genetics. By studying the effects of a single mutated gene on the phenotype of a specimen, researchers can measure the extent of that gene’s pleiotropy. One such study, which measured pleiotropy levels across yeast cells with individual deletion mutations, found that one in three yeast genes had a significant relationship with more than one trait. Another common research method, QTL (Quantitative Trait Locus), links genetic variation with statistical changes in continuous quantitative traits like height and weight. QTL studies can find some pleiotropic genes that reverse genetics studies fail to see, but they still fail to find statistically significant gene-to-trait relations in the majority of cases.

In Medical Practice
When treating patients, an understanding of pleiotropic genes lends itself to much more accurate diagnoses. Because single mutations can cause distinctive change in seemingly unrelated body systems, specific combinations of symptoms can lead doctors to diagnose diseases directly related to one gene’s mutation. The PTEN gene, when mutated, can cause Cowden Syndrome (CS) and, more broadly, PTEN hamartoma tumor syndrome (PHTS). The diagnosis process confers many telltale signs of pleiotropy. Because the process is different for adults and children, a developmental change in PTEN use is expected. In children, PTEN mutation causes symptoms in any of four seemingly unrelated systems: a mental disorder, dermatological features, vascular malformations, and gastrointestinal polyps. Because researchers discovered the relation between all these symptoms and the PTEN gene, doctors can now diagnose PHTS with much higher confidence as a pleiotropic gene disorder.