A radioimmunoassay with polyclonal antibodies against wild-type atrial natriuretic peptide (ANP), mutant ANP (mANP), and B-type natriuretic peptide (BNP) shows levels of circulating mANP that are 5 to 10 times higher than the levels of ANP in two family members with the NPPA mutation (in Subject III-2 during chronic atrial fibrillation and in Subject III-6 during normal sinus rhythm). In the affected subjects, plasma ANP and BNP levels are normal. Low-level cross-reactivity of the polyclonal anti-mANP antibody was observed in samples from unaffected subject (Subject III-5) and in five control subjects (three female [F] and two male [M]).

Squares indicate male subjects, and circles female subjects. Black denotes affected subjects, and white unaffected subjects; gray indicates that the status of the subject is unknown. A slash through the symbol indicates that the subject is deceased. The gene for atrial natriuretic peptide (NPPA) is located at 1p36-p35. Markers that were tested for this region of chromosome 1 are listed in order from the p-terminal end of the chromosome, with map locations according to the Web site of the National Center for Biotechnology Information (www.ncbi.nlm.nih.gov) and given in megabases and centimorgans. A common c.454C→T polymorphism in exon 3 of wild-type NPPA is included, along with the NPPA mutation (NPPA mut). The haplotypes for these markers are shown in columns beneath family members who underwent genetic evaluation; the disease-associated haplotypes are boxed. Two subjects (III-7 and III-9) inherited portions of the disease haplotype, but not the disease gene, as a result of recombination events.

In Panel A, a representative monophasic action potential (MAP) is shown at baseline and after a 40-minute perfusion with 100 nM of wild-type atrial natriuretic peptide (ANP). MAP duration at 90% repolarization (MAPD₉₀) was not significantly changed by ANP. In Panel B, a representative MAP after a 40-minute perfusion with the mutant form of ANP (mANP) shows a shortening of MAPD₉₀ from 47 to 41 msec. In Panel C, mANP (N = 8 hearts) and wild-type ANP (N = 10 hearts) perfusion for 40 minutes shows a significant decrease in MAPD₉₀ for mANP as compared with the baseline value (9±2 msec, P = 0.005) but not for wild-type ANP (0.7±1.7 msec, P = 0.87). The difference in the change in MAPD₉₀ between mANP and wild-type ANP was also significant (P = 0.008). In Panel D, mANP (N = 7 hearts) and wild-type ANP (N = 6 hearts) perfusion for 40 minutes resulted in a trend toward a reduction in the effective refractory period (ERP), as compared with the baseline value, for mANP (7.1±2.4 msec, P = 0.08) but not for wild-type ANP (P = 0.43). The difference in the change in ERP between mANP and wild-type ANP was significant (P = 0.03). The T bars denote standard errors.