POLD1 and mandibular hypoplasia-deafness-progeroid syndrome: Once we confirmed the heterozygous c.1812_1814delCTC variant in MSC from MDPL patients (i.e., BRY, LRX and PX) by Sanger sequencing of POLD1 gene, we evaluated DNA polymerase δ protein expression levels by Western blot analysis to assess the phenotype of POLD1 p.Ser605del variant at protein level in different patients (Figure 3A).