Recent in vitro studies using human cell lines showed that MCM10 is critical for human telomere replication and suggest that defective telomere maintenance caused both MCM10-associated natural killer (NK) cell deficiency and restrictive cardiomyopathy with hypoplasia of the spleen and thymus (Baxley et al., 2021; Mace et al., 2020). The gene discussed is MCM10; the disease is restrictive cardiomyopathy.