Testing subject GM09276 from Coriell cell repositories, an index kindred with carboxypeptidase N deficiency, researchers found three variants in CPN1-G178D. Two of these, this variant and another causing a frameshift, they implicated in causing the disease in a recessive manner. They found this variant in one out of 256 control chromosomes. The authors hypothesize that this variant (G178D) causes reduced function rather than a total loss as the subject had 20% of normal enzyme activity.
They don’t report studying any other cases nor other family members, possibly those samples weren’t available. According to Coriell, GM09276 was 73 years old at time of sampling, had “Angioedema, about 40 attacks per year; urticaria on a few occasions during childhood; long-standing ragweed hay fever and asthma; proband and a sister have approximately 20% of normal carboxypeptidase N activity in serum”.