Promotion Effects of Smoking in Polyp Development in Monozygotic Twins with Atypical Colorectal Polyposis

<jats:p>Smoking is a known risk factor for the development of colorectal polyps. Even in familial adenomatous polyposis and serrated polyposis syndrome, smoking is a risk factor of the development of polyps. Here, we report a case of monozygotic twins with atypical colorectal polyposis showing lots of hyperplastic polyps and adenomas and describe how the polyposis developed differently in the brothers based on the presence or absence of smoking. The case was of a set of monozygotic male twins, and the twins were in their 50s. The younger brother smoked 40 cigarettes a day since he was 16 years old. The older brother had smoked about 25 cigarettes a day since he was 16 years old but stopped smoking after he was diagnosed with polyposis. As we previously reported, we managed to remove polyps as much as possible from both twins without surgery. The median number of removed polyps (IQR: 25–75%) per colonoscopy for 20 years was 9.0 (3.5–14.8) in the older brother and 20.5 (7.5–35.5) in the younger brother. There was a significant difference between the twins (p &#x3c; 0.01). Additionally, genetic tests found that the twins carried a rare missense variant of BRCA2, and this variation has not been previously reported. In conclusion, these monozygotic twins with atypical colorectal polyposis showing a new variant of BRCA2 suggest that smoking is related to the development of colorectal polyps. Further analysis will be required for the identified BRCA2 variant in possible involvement in the development of atypical polyposis. </jats:p>