Mosaic RASopathies: A review of disorders caused by somatic pathogenic variants in the genes of the RAS/MAPK pathway

KRIT1 in vascular biology and beyond

KRIT1 is a 75 kDa scaffolding protein which regulates endothelial cell phenotype by limiting the response to inflammatory stimuli and maintaining a quiescent and stable endothelial barrier. Loss-of-function mutations in KRIT1 lead to the development of cerebral cavernous malformations (CCM), a disease marked by the formation of abnormal blood vessels which exhibit a loss of barrier function, increased endothelial proliferation, and altered gene expression. While many advances have been made in our understanding of how KRIT1, and the functionally related proteins CCM2 and PDCD10, contribute to the regulation of blood vessels and the vascular barrier, some important open questions remain. In addition, KRIT1 is widely expressed and KRIT1 and the other CCM proteins have been shown to play important roles in non-endothelial cell types and tissues, which may or may not be related to their role as pathogenic originators of CCM. In this review, we discuss some of the unsettled questions regarding the role of KRIT1 in vascular physiology and discuss recent advances that suggest this ubiquitously expressed protein may have a role beyond the endothelial cell.

Calcified Sclero-Choroidal Choristomas in Mosaic RASopathies: A Description of a New Imaging Sign

PURPOSE

To evaluate the imaging and clinical features of unusual calcified lesions seen in the fundus of patients with mosaic RASopathy.

DESIGN

Single-center retrospective observational study.

SUBJECTS

Ten eyes with calcified fundus lesions in 7 patients with mosaic RASopathy.

METHODS

The lesions were evaluated with fundus photography, oral fundus fluorescein angiography, B-scan ultrasonography, magnetic resonance imaging (MRI), and computed tomography (CT) scan where available.

MAIN OUTCOME MEASURES

The imaging characteristics of calcified fundus lesions were assessed.

RESULTS

We found 7 patients with mosaic RASopathies, 5 men and 2 women (3 with linear sebaceous nevus syndrome, 3 with oculoectodermal syndrome, and 1 with encephalocraniocutaneous lipomatosis) with molecular confirmation in 5 cases, all 5 having KRAS-pathogenic variants. Calcified fundus lesions were identified in 10 eyes (bilateral in 3 patients), appearing as slightly elevated, creamy-yellow lesions around or adjacent to the optic nerve, extending supero-nasally; all but 2 of these lesions involved both the choroid and sclera, with 2 of them only involving the sclera at the time of examination. One case developed a choroidal neovascular membrane necessitating intravitreal bevacizumab injections. All 7 patients had B-scan ultrasonography, and the lesion appeared as a hyperechogenic area with an acoustic shadow posteriorly despite reduced gain. Five patients had MRI, and where fundus lesions were present, there was a focal defect in the sclero-choroidal layer. Four patients had a CT scan, and all 4 showed calcifications affecting both the posteromedial sclero-choroid and adjacent medial rectus muscle. Two of these patients had normal eye movements, 1 had a unilateral fixed adducted eye and a vestigial fibrous medial rectus muscle seen in imaging and intraoperatively, and the fourth had marked exotropia with a right gaze deficit affecting both eyes.

CONCLUSIONS

We propose that the lesions seen in this cohort are calcified sclero-choroidal choristomas and should be suspected in mosaic RASopathies when creamy-yellow lesions are seen in the fundus. If identified, the possibility of choroidal neovascularization should be considered during follow-up. In all cases where a CT scan was performed, a novel sign of sclero-muscular calcification involving the medial rectus muscle was seen.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Molecular Basis and Diagnostic Approach to Isolated and Syndromic Lateralized Overgrowth in Childhood

OBJECTIVE

To demonstrate a high-yield molecular diagnostic workflow for lateralized overgrowth (LO), a congenital condition with abnormal enlargement of body parts, and to classify it by molecular genetics.

STUDY DESIGN

We categorized 186 retrospective cases of LO diagnosed between 2003 and 2023 into suspected Beckwith-Wiedemann spectrum, PIK3CA-related overgrowth spectrum (PROS), vascular overgrowth, or isolated LO, based on initial clinical assessments, to determine the appropriate first-tier molecular tests and tissue for analysis. Patients underwent testing for 11p15 epigenetic abnormalities or somatic variants in genes related to PI3K/AKT/mTOR, vascular proliferation, and RAS-MAPK cascades using blood or skin DNA. For cases with negative initial tests, a sequential cascade molecular approach was employed to improve diagnostic yield.

RESULTS

This approach led to a molecular diagnosis in 54% of cases, 89% of cases consistent with initial clinical suspicions, and 11% reclassified. Beckwith-Wiedemann spectrum was the most common cause, with 43% of cases exhibiting 11p15 abnormalities. PIK3CA-related overgrowth spectrum had the highest confirmation rate, with 74% of clinically diagnosed patients showing a PIK3CA variant. Vascular overgrowth demonstrated significant clinical overlap with other syndromes. A molecular diagnosis of isolated LO proved challenging, with only 21% of cases classifiable into a specific condition.

CONCLUSIONS

LO is underdiagnosed from a molecular viewpoint and to date has had no diagnostic guidelines, which is crucial for addressing potential cancer predisposition, enabling precision medicine treatments, and guiding management. This study sheds light on the molecular etiology of LO, highlighting the importance of a tailored diagnostic approach and of selecting appropriate testing to achieve the highest diagnostic yield.