In agreement with this, we later identified a germline missense mutation of MDM4, encoding a major negative regulator of p53, in a familial syndrome of neutropenia and defective telomere maintenance, and we could correlate p53 activation with decreased RTEL1 expression and short telomeres in the most affected family member as well as in mice carrying the same Mdm4 mutation (Toufektchan et al., 2020). The gene discussed is MDM4; the disease is neutropenia.