Molecular and in silico analyses validates pathogenicity of homozygous mutations in the NPR2 gene underlying variable phenotypes of Acromesomelic dysplasia, type Maroteaux

Abstract Homozygous and/or heterozygous loss of function mutations in the natriuretic peptide receptorB ( NPR2) have been reported in causing acromesomelic dysplasia, type Maroteaux with variable clinical features and idiopathic short staturewith nonspecific skeletal deformities. On the other hand, gain of function mutations in the same gene result in overgrowth disorder suggesting that NPR2and its ligand, natriuretic peptide precursor C(CNP), are the key players of endochondral bone growth. However, the precise mechanism behind phenotypic variability of the NPR2mutations is not fully understood so far. In the present study, three consanguineous families of Pakistani origin (A, B, C) with variable phenotypes of acromesomelic dysplasia, type Maroteaux were evaluated at clinical and molecular levels. Linkage analysis followed by Sanger sequencingof the NPR2gene revealed three homozygous mutations including p.(Leu314 Arg), p.(Arg371*), and p.(Arg1032*) in family A, B and C, respectively. In silico structural and functional analyses substantiated that a novel missense mutation [p.(Leu314 Arg)] in family A allosterically affects binding of NPR2homodimer to its ligand (CNP) which ultimately results in defective guanylate cyclaseactivity. A nonsense mutation[p.(Arg371*)] in family B entirely removed the transmembrane domain, protein kinase domainand guanylate cyclasedomains of the NPR2resulting in abolishing its guanylate cyclaseactivity. Another novel mutation [p.(Arg1032*)], found in family C, deteriorated the guanylate cyclasedomain of the protein and probably plundered its guanylate cyclaseactivity. These results suggest that guanylate cyclaseactivity is the most critical function of the NPR2and phenotypic severity of the NPR2mutations is proportional to the reduction in its guanylate cyclaseactivity.