A Prevalent <scp><i>TMEM260</i></scp> Deletion Causes Conotruncal Heart Defects, Including Truncus Arteriosus

Conotruncal heart defects are severe congenital malformations of the outflow tract, including truncus arteriosus (TA) and double-outlet right ventricle (DORV). TA is a severe congenital heart disease (CHD) in which the main arterial outflow tract of the heart fails to separate. We recently reported TMEM260 (NM_017799.4), c.1617del (p.Trp539Cysfs*9), as a major cause of TA in the Japanese population (TMEM260 Keio-Tohoku variant) comparable to the prevalence of the 22q11.2 deletion syndrome, which accounts for 12%-35% of TA. However, no other major causes of TA have not been identified. Here, we report a family that included a TA patient and a DORV patient, harboring the compound heterozygous variants of TMEM260, a 7066-bp deletion encompassing exons 6-7 and c.1393C > T, p.(Gln465*). The allele frequency of the 7066-bp deletion was particularly high in the Japanese population (0.17%). Based on the allele frequency of this deletion and c.1617del (0.36%) in the Japanese population, TMEM260 variants might be associated with more than half of the Japanese patients with TA. This study showed that TMEM260 pathogenic variants might be the most common cause of TA in the Japanese population and could explain the wide spectrum of phenotypes associated with TMEM260-related CHD, including DORV, demonstrating the usefulness of genetic testing in Japanese patients with TA.