MEK Inhibition in a Newborn with RAF1-Associated Noonan Syndrome Ameliorates Hypertrophic Cardiomyopathy but Is Insufficient to Revert Pulmonary Vascular Disease

Abstract

The RAF1:p.Ser257Leu variant is associated with severe Noonan syndrome (NS), progressive hypertrophic cardiomyopathy (HCM), and pulmonary hypertension. Trametinib, a MEK-inhibitor approved for treatment of RAS/MAPK-mutated cancers, is an emerging treatment option for HCM in NS. We report a patient with NS and HCM, treated with Trametinib and documented by global RNA sequencing before and during treatment to define transcriptional effects of MEK-inhibition. A preterm infant with HCM carrying the RAF1:p.Ser257Leu variant, rapidly developed severe congestive heart failure (CHF) unresponsive to standard treatments. Trametinib was introduced (0.022 mg/kg/day) with prompt clinical improvement and subsequent amelioration of HCM at ultrasound. The appearance of pulmonary artery aneurysm and pulmonary hypertension contributed to a rapid worsening after ventriculoperitoneal shunt device placement for posthemorrhagic hydrocephalus: she deceased for untreatable CHF at 3 months of age. Autopsy showed severe obstructive HCM, pulmonary artery dilation, disarrayed pulmonary vascular anatomy consistent with pulmonary capillary hemangiomatosis. Transcriptome across treatment, highlighted robust transcriptional changes induced by MEK-inhibition. Our findings highlight a previously unappreciated connection between pulmonary vascular disease and the severe outcome already reported in patients with RAF1-associated NS. While MEK-inhibition appears a promising therapeutic option for HCM in RASopathies, it appears insufficient to revert pulmonary hypertension.

Keywords: MEK-inhibitor; Noonan syndrome; RASopathies; hypertrophic cardiomyopathy; therapeutics; transcriptomics.

Figure 1

Treatment time course. The picture shows changes in nt-pro-BNP, Left Ventricular Outflow (LVO) gradient and septal thickness at ultrasound before and after treatment initiation and related to the major clinical events in our patient.

Figure 2

Evolution over time of hypertrophic cardiomyopathy (HCM). Pre-treatment US (first column) shows severe HCM at M-mode Left Ventricle (Mm-LV, first row), short-axis LV (second row) and LV outflow track obstruction (CW-Doppler, third row), few days before treatment start. The best result under treatment is shown in the middle column: Mm-LV in first row, short-axis LV (second row) and LV outflow track obstruction (third row) demonstrated a consistent reduction of LV thickness and improvement of LV outflow track obstruction. The third column shows cardiac US three days before death: pulmonary artery dilatation is evident in the first row (2D), the rapid worsening of HCM, both in terms of LV thickness and obstruction are depicted in the last 2 rows (short-axis LV and CW-Doppler, respectively).

Figure 3

Gross pathology findings. Autopsy showed typical Noonan syndrome (NS) features with low-set posteriorly rotated ears, high anterior hairline with wide forehead and narrow temples, mild hypertelorism, downslanting palpebral fissures, broad nose, full tip with deeply grooved philtrum (a), pterigium colli, short webbed neck (b), severe obstructive HCM (c,e), dilation of pulmonary artery trunk and branches (d).

Figure 4

Histology showed a complete disarray of both gross and fine cardiac and pulmonary anatomy. Heart microscopy showed disorientation of muscle fibers and hypertrophic myocells with enlarged ovoid nucleus (a), left ventricle fibrotic and necrotic areas of myocells (long-standing infarction) and limited neighboring areas of more recent ischemic damage (b). Picture of the lungs with arterial hypertension, chronic stasis and alveolar damage: pulmonary capillary hemangiomatosis with peripheral arterioles with stenotic lumen for muscular tunic hypertrophy, intimal tunic thickening, hilar pulmonary vessels of increased caliber and with hypertrophic wall, thickened and hypervascularized interalveolar septa, alveolar lumens with exudate and foamy histiocytes containing hemosiderin (c), and increased thickness of the interalveolar septum with hypercapillarization (d). The capillaries (colored in brown with immunohistochemical staining CD31) were markedly increased in with a chaotic distribution (hemangiomatosis) with most of them not reaching the alveolar surface (e).

Figure 5

GSEA analysis of trametinib-driven pathway signature dynamics in the PBMC transcriptome. All signatures display a consistently negative Enrichment Score, below the −1.5 significance threshold value, indicating overall down-modulation by trametinib over the entire treatment period. (A) Modulation of signatures related to the EGFR/RAS/RAF/MEK pathway. These include the PTPN11 RASopathy signature, highlighted by the black dashed line. (B) Modulation of signatures associated with additional pathways, including the YAP/TAZ pathway signature highlighted by the red dashed line.