Hypertrophy of lymphoid organs is a possible phenotypic characteristic of R420W mutation of the cardiac ryanodine receptor gene: A study using a knock-in mouse model

• Mice with R420W mutation of RyR2 exhibit hypertrophy of lymphoid organs.
• Phenotypic changes may imply existence of hereditary arrhythmia diseases.
• Phenotypic changes may suggest the presence of the R420W mutation.
• Sudden unexplained death cases with mutation may show such findings at autopsy.
• Mouse model resembles the previously termed “status thymicolymphaticus”.

Cardiac ryanodine receptor gene (RyR2) mutations sometimes result in sudden cardiac death due to fatal arrhythmias. N-terminal R420W mutation of RyR2 is known to show similar phenotypes to arrhythmogenic right ventricular cardiomyopathy and to cause juvenile sudden death. We previously reported two sudden death cases with the same R420W mutation. Interestingly, the cases showed hypertrophy of lymphoid organs such as the thymus and mesenteric lymph nodes. The present study examined whether R420W mutation of RYR2 causes hypertrophy of lymphoid organs by generating a mouse model carrying the mutation. Homozygous (RyR2R420W/R420W) mice showed significant increases in thymus and spleen weights but not in kidney, heart, and brain weights compared with wild-type mice. The mice also showed remarkable hypertrophy of mesenteric lymph nodes. Immunohistochemical study revealed that RyR2 protein was prominently expressed in epithelial cells of the thymic medulla in the thymus. These findings show that mice with R420W mutation of RyR2 exhibit hypertrophy of lymphoid organs. Sudden unexplained death cases with the mutation may display such findings at autopsy.