Gamma-glutamyl carboxylase (GGCX) mutations have been reported in patients with a pseudoxanthoma elasticum (PXE)-like phenotype, loose redundant skin, and multiple vitamin K-dependent coagulation factor deficiencies. We report on the clinical findings and molecular results in 13 affected members of two families who had a uniform phenotype consisting of (PXE)-like skin manifestations in the neck and trunk, loose sagging skin of the trunk and upper limbs, and retinitis pigmentosa confirmed by electroretinographies in 10 affected individuals. There were no coagulation abnormalities. Molecular investigations of the ATP-binding cassette subfamily C member 6 did not yield causative mutations. All 13 affected family members were found to be homozygous for the splice-site mutation c.373+3G>T in the GGCX gene. All tested parents were heterozygous for the mutation, and healthy siblings were either heterozygous or had the wild type. We suggest that the present patients represent a hitherto unreported phenotype associated with GGCX mutations. Digenic inheritance has been suggested to explain the variability in phenotype in GGCX mutation carriers. Consequently, the present phenotype may not be explained only by the GGCX mutations only but may be influenced by variants in other genes or epigenetic and environmental factors.