Identification of Codon 146 KRAS Variants in Isolated Epidermal Nevus and Multiple Lesions in Oculoectodermal Syndrome: Confirmation of the Phenotypic Continuum of Mosaic RASopathies

Mosaic RASopathies concept: different skin lesions, same systemic manifestations?

BACKGROUND

Cutaneous epidermal nevi are genotypically diverse mosaic disorders. Pathogenic hotspot variants in HRAS, KRAS, and less frequently, NRAS and BRAF may cause isolated keratinocytic epidermal nevi and sebaceous nevi or several different syndromes when associated with extracutaneous anomalies. Therefore, some authors suggest the concept of mosaic RASopathies to group these different disorders.

METHODS

In this paper, we describe three new cases of syndromic epidermal nevi caused by mosaic HRAS variants: one associating an extensive keratinocytic epidermal nevus with hypomastia, another with extensive mucosal involvement and a third combining a small sebaceous nevus with seizures and intellectual deficiency. Moreover, we performed extensive literature of all cases of syndromic epidermal nevi and related disorders with confirmed pathogenic postzygotic variants in HRAS, KRAS, NRAS or BRAF.

RESULTS

Most patients presented with bone, ophthalmological or neurological anomalies. Rhabdomyosarcoma, urothelial cell carcinoma and pubertas praecox are also repeatedly reported. KRAS pathogenic variants are involved in 50% of the cases, especially in sebaceous nevi, oculoectodermal syndrome and encephalocraniocutaneous lipomatosis. They are frequently associated with eye and brain anomalies. Pathogenic variants in HRAS are rather present in syndromic keratinocytic epidermal nevi and phacomatosis pigmentokeratotica.

CONCLUSION

This review delineates genotype/phenotype correlations of syndromic epidermal nevi with somatic RAS and BRAF pathogenic variants and may help improve their follow-up.

Encephalocraniocutaneous Lipomatosis: A Case Report

ABSTRACT

Encephalocraniocutaneous lipomatosis (ECCL) is a rare congenital syndrome and subclassification of oculoectodermal syndrome. Encephalocraniocutaneous lipomatosis may be associated with postzygotic mutations. However, absence of an identifiable mutation does not preclude a diagnosis of ECCL. Encephalocraniocutaneous lipomatosis commonly causes skin, eye, and central nervous system anomalies. Diagnosis can be made through genetic sequencing or standardized clinical criteria. One clinically apparent major criterion for the diagnosis of ECCL is nevus psiloliparus (NP), a fatty nevus with overlying nonscarring alopecia. In this case, a 50-day-old female infant with uncomplicated birth history presented to dermatology clinic for evaluation of 2 superficial cranial masses that had been present since birth without regression or evolution. One of the masses was located within the hairline and demonstrated overlying nonscarring alopecia, suspicious of NP. Because of concern for ECCL, brain magnetic resonance imaging was ordered and revealed 2 intracranial lipomas. Genetic testing was inconclusive. Excision of the masses was performed at the request of the parents for cosmetic purposes. Histologic evaluation of the surgical specimens confirmed the diagnosis of NP and ECCL. A suspected NP should raise concern for ECCL and prompt further evaluation for systemic involvement. In particular, patients with suspected ECCL should be screened for ocular and CNS involvement. Early identification and diagnosis are important for prognostication because patients with ECCL are at increased risk of developing neoplasms of the head and neck and may require more frequent screening examinations.

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

Mosaic RASopathies are a heterogeneous group of diseases characterized by the presence at birth or early onset of congenital anomalies, cutaneous and vascular anomalies, segmental overgrowth, and increased cancer risk. They are caused by somatic pathogenic variants of the genes belonging the RAt Sarcoma Mitogen-activated protein kinase (RAS/MAPK) pathway causing its hyperactivation. Here, we review the clinical and molecular characteristics of this heterogeneous group of diseases, including the possibilities of molecular diagnosis and new therapeutic perspectives.