In a study of 11 idiopathic cases of infantile arterial calcification, this variant was reported homozygously in one case and heterozygously in combination with L579F (in cis) and a frameshift (in trans) in another. Counting alleles, this is a case+: 3, case-: 19. If we use the combined data from dbSNP, control+: 8, control-: 190. This has p=0.08.
The footnote to Table 3 states: “The mutation reported in this paper (c.2320C>T [p.Arg774Cys]) has since been shown to be a polymorphism (rs28933977) with a minor allele frequency of 5%.”
These authors follow up on the homozygous case from Rutsch et al, a Turkish family, and find the patient is also homozygous for E266V. The father is homozygous for the E266V variant as well but has a later onset phenotype, developing an aortic root dissection at the age of 28 yrs.