Complicated ventricular arrhythmia and hematologic myeloproliferative disorder in RIT1‐associated Noonan syndrome: Expanding the phenotype and review of the literature

Abstract

Background

Noonan syndrome is an autosomal dominant disorder secondary to RASopathies, which are caused by germ‐line mutations in genes encoding components of the RAS mitogen‐activated protein kinase pathway. RIT1 (OMIM *609591) was recently reported as a disease gene for Noonan syndrome.

Methods and Results

We present a patient with RIT1‐associated Noonan syndrome, who in addition to the congenital heart defect, had monocytosis, myeloproliferative disorder, and accelerated idioventricular rhythm that was associated with severe hemodynamic instability. Noonan syndrome was suspected given the severe pulmonary stenosis, persistent monocytosis, and “left‐shifted” complete blood counts without any evidence of an infectious process. Genetic testing revealed that the patient had a heterozygous c.221 C>G (pAla74Gly) mutation in the RIT1.

Conclusion

We report a case of neonatal Noonan syndrome associated with RIT1 mutation. The clinical suspicion for Noonan syndrome was based only on the congenital heart defect, persistent monocytosis, and myeloproliferative process as the child lacked all other hallmarks characteristics of Noonan syndrome. However, the patient had an unusually malignant ventricular dysrhythmia that lead to his demise. The case highlights the fact that despite its heterogeneous presentation, RIT1‐associated Noonan syndrome can be extremely severe with poor outcome.

Abstract

RIT1 is one of the most recent genes identified in association with Noonan Syndrome. In this report, we present a patient with RIT1‐associated Noonan syndrome, who had pulmonary valve stenosis, monocytosis, myeloproliferative disorder, and hemodynamically significant ventricular dysrhythmias. Genetic testing revealed that the patient had a heterozygous c.221 C>G (pAla57Gly) mutation in the RIT1 gene.