IMPE Abstracts

Background and object: C-type natriuretic peptide (CNP) and its receptor Atrial natriuretic peptide receptor 2 (NPR2) are expressed in the hypertrophic region of the growth plate and are major regulators of endochondral ossification. CNP-NPR2 stimulates the synthesis of chondrocytes and cartilage matrix and promotes growth plate development. Heterozygous loss-of-function variants in NPR2 gene cause short stature with nonspecific skeletal abnormalities (OMIM#616255), accounting for about 2~6% of ISS. rhGH treatment is beneficial for short-stature patients with NPR2heterozygous variants. However, data on the ISS as a result of the NPR2 gene variants remain relatively limited. Besides, related genotype-phenotype and Growth hormone therapy efficacy correlations require functional and clinical analysis, which include age, treatment dose, and duration. Here, we aimed to analyze and identify pathogenic variants in NPR2gene and explore the therapeutic response to recombinant growth hormone (rhGH).

Methods: NPR2 was sequenced in two Chinese Han patients with ISS via next generation sequencing, and in vitro functional experiments, homology modeling and molecular dynamics simulation analysis or transcript analysis of variants was performed to examine putative protein changes and pathogenicity of the variants. Two patients received rhGH therapy for two years.

Results: Two NPR2 heterozygous variants were identified in unrelated cases: c.1579C>T, p. Leu 527P he in patient 1, and c.2842dup C,p. His948Profs*5 in patient 2. Functional studies showed that both NPR2 variants, His948Profs*5 failed to produce cGMP in the homozygous state. Furthermore, we verified that the stimulatory effect of ATP on CNP-dependent guanylyl cyclase activity was almost unresponsive in Leu527Phe variant of NPR2, which has not been previously reported. The age of both patients at the start of treatment was 4.5 and 6.5 years old, and their height increased by 1.59 ± 0.1 SDS after 2 years of treatment. No significant side-effects were noted during the course of treatment.

Conclusion: In conclusion, we report 2 cases of novel pathogenic mutations in the NPR2 gene. The Leu527Phe variant in KHD that significantly decreases the stimulatory effect of ATP on CNP-dependent guanylyl cyclase activity, resulting in loss-of-function. This study enriches our knowledge of the NPR2 gene mutation spectrum. GH therapy may be an effective approach to improve height in patients with heterozygous mutations in the NPR2 gene, particularly those located in the cytosolic compartment.