Since PXE is an autosomal recessive disorder, and the heterozygous carriers of the mutations or the mice heterozygous for the SNP polymorphism do not show evidence of mineralization, these results suggest that the critical level for the expression of the mineralization phenotype is somewhere between 25% and 50% of the normal level of ABCC6. The gene discussed is ABCC6; the disease is Pseudoxanthoma elasticum.