ERCC4 and XFE progeroid syndrome: Ercc1 hypomorphic mice (Ercc1d/−), expressing one Ercc1 null allele and one mutant Ercc1 allele carrying a 7 amino acid deletion at the C-terminus of the protein, better mimic the human XFE progeroid syndrome caused by reduced expression of ERCC1-XPF, and develop healthy until early adulthood, after which rapid, progressive, premature aging occurs [29].