Natural history of MRAS‐related Noonan syndrome: Evidence of mild adult‐onset left ventricular hypertrophy and neuropsychiatric features

Gain of function pathogenic variants in MRAS have been found in a small subset of pediatric subjects presenting with Noonan syndrome (NS) associated with hypertrophic cardiomyopathy (HCM) and moderate to severe intellectual disability. These variants are considered to confer a high‐risk for the development of severe HCM with poor prognosis and fatal outcome. We report on the natural history of the first adult subject with NS carrying the recurrent pathogenic p.Thr68Ile amino acid substitution. Different from what had previously been observed, he presented with a mild, late‐onset left ventricular hypertrophy, and a constellation of additional symptoms rarely seen in NS. The present case provides evidence that HCM does not represent an obligatory, early‐onset and severe complication in subjects with MRAS variants. It also adds new data about late‐onset features suggesting that other unexpected complications might be observed in adult subjects providing anticipatory guidance for individuals of all age.

Usually, HCM has an early-onset, with a greater rate of congestive heart failure, left ventricular outflow obstruction, and earlier mortality with respect to other pediatric forms of HCM (Lioncino et al., 2022). NS has been associated with pathogenic variants in more than 12 genes encoding proteins with a role in the RAS-MAPK signaling pathway , and is mainly transmitted as an autosomal dominant trait with a high proportion of de novo mutations. Rare recessive forms associated with biallelic inactivating variants in LZTR1 and SPRED2 have been recently identified, as well (Johnston et al., 2018;Motta et al., 2021).
All of them had moderate to severe ID and showed severe HCM, which was fatal in two cases during the first months of life (Motta et al., 2020;Pires et al., 2021). Here, we describe the natural history of the first adult subject with the recurrent p.Thr68Ile substitution presenting with NS, who showed ID and developed mild late-onset left ventricular hypertrophy associated with a rare cardiac malformation (i.e., interatrial septal aneurism [IASA]) and mitral valve prolapse.
He also presented with additional clinical features previously unreported in MRAS-related NS and extremely rare in the overall NS population, which recommend a specific long-term follow-up.

| CLINICAL REPORT
The proband is a 40-year-old man, the first son of nonconsanguineous healthy parents. He has two healthy brothers and two sisters. The mother had five first-trimester miscarriages during her reproductive life. He was born at term by Cesarean section because of multiple umbilical cord wrapping around the neck, after an uneventful pregnancy. His birth weight was 3,300 g (À0.42 SD, 34 centile), birth length and occipital-frontal circumference (OFC) not being reported.
He had psychomotor delay: head control was achieved at 4 months, he sat autonomously at 8 months, walked alone at 15 months, and pronounced his first words at 4 years. At 5 years, slight abnormalities in the EEG pattern without clinical relevance were noted. He subsequently suffered from complex partial seizures at 14 years, for which he was pharmacologically treated with carbamazepine and partially controlled. At 7 years and 7 months, growth parameters were as follows: height 119 cm (À1.15 SD, 12th centile), weight 23.5 kg (À0.30 SD, 38th centile), and OFC 55 cm (+2 SD, 98th centile). At 14 years, right convex scoliosis, dorsal kyphosis, and pectus carenatum were documented. At 19 years, he developed psychiatric symptoms with easily provoked outburst, heteroaggressive and autoaggressive behavior, foul language, destructive and inappropriate social behavior, autistic closure with a diagnosis of schizophrenic psychosis, which was pharmacologically treated with multidrug therapy. At 20 years, a lipoma at the right forearm with axillary reactive lymph nodes was surgically removed.  (Higgins et al., 2017;Motta et al., 2020;Pires et al., 2021). The variant was validated by Sanger sequencing, which also confirmed its presence in genomic DNA extracted from cultured fibroblasts. Parental DNA specimens were not available for segregation analysis. Since the occurrence of the unusual psychiatric features, exome sequencing was also performed using DNA from peripheral blood leukocytes (Supplemental Methods of Appendix S1), which excluded the occurrence of additional clinically relevant variants in genes implicated in neurobehavioral and psychiatric disorders (Table S1).  (Liau et al., 2022). The Thr68Ile substitution is located in a region that does not directly interact with the ternary complex MRAS-SHOC2-PP1C, but has been demonstrated to maintain the GTPase in its active GTP-bound conformation and has been proved to promote a more stable translocation of the SHOC2-PP1C complex to the plasma membrane, leading to an enhanced activation of the MAPK pathway (Liau et al., 2022;Motta et al., 2020;Young et al., 2018). to confer a high-risk for the development of severe HCM with poor prognosis and fatal outcome. To the best of our knowledge, the present subject represents the first report of MRAS-related NS who shows mild cardiac involvement (IASA and mild mitral valve prolapse).

| DISCUSSION
IASA is an unusual CHD; it has rarely been seen in NS subjects, who show ventricular septum aneurysms more frequently (Otsuka et al., 2006). This finding has a relevant importance in long-term follow-up, being IASA associated with a higher risk for cerebrovascular events (Gallet et al., 1985). It is possible that other MRAS-related NS individuals may not have been evidenced with IASA due to their young age or premature death. Of note, the p.Thr68Ile change has been found twice in patients with HCM and other associated CHDs: atrial septum defect (ASD) and PVS (Higgins et al., 2017) and ASD with left ventriculum apical aneurism (LVAA) (Pires et al., 2021).
Among them, LVAA seems to be the most functionally related anomaly with IASA.
The present subject presented with complex partial seizures at tures combined with overgrowth of surrounding tissues, whose characterization may also include histological description ascribed to lipomas (Eijkelenboom et al., 2019). Most of the identified variants are known pathogenic substitutions with oncogenic behavior, mainly located at residues 12, 13, 61, and 146. In seven cases, a somatic duplication of 7-10 amino acid residues within the switch II region was identified. Previously, two unrelated subjects affected with mild CS and carrying an overlapping in-frame duplication (p.Glu63_Asp69dup) have been described (Lorenz et al., 2013;Xu, Wang, Lin, & Yu, 2015). A similar somatic and an addition germinal insertion in KRAS have been found in one VMOS and in one NS individual, respectively (Eijkelenboom et al., 2019). They are all located very near to or comprising the Thr58 residue, which is homologous to the Thr68 residue of MRAS. All these variants have been proved to act as weakly but constitutively activating substitutions determining an increased affinity for the RAS binding domain of RAF proteins.
Although it would have been interesting to more accurately classify the nature of the lesion that was histologically identified as lipoma, soft tissue MRI could not be performed in order to verify a possible vascularization. Unfortunately, residual specimens were not available for further analyses due to long time from the first evaluation.
The present report emphasizes the relevance of reaching a molecular diagnosis in adult patients in terms of generating new knowledge. The profiling of the natural history in rare diseases is also of great value in long-term follow-up and managing of concomitant diseases whose course might be exacerbated by the pre-existing genetic disorder, eventually improving their healthcare outcomes. In this specific case, the presence of IASA suggests a higher risk for cerebrovascular events, recommending high blood pressure accurate monitoring and treatment. Conceptualization, writing -original draft preparation; Data curation.