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.

The pathophysiology of bilateral and multifocal Wilms tumors: What we can learn from the study of predisposition syndromes

Approximately 5% of patients with Wilms tumor present with synchronous bilateral disease. The development of synchronous bilateral Wilms tumor (BWT) is highly suggestive of a genetic or epigenetic predisposition. Patients with known germline predisposition to Wilms tumor (WT1 variants, Beckwith Wiedemann spectrum, TRIM28 variants) have a higher incidence of BWT. This Children's Oncology Group (COG)-International Society for Pediatric Oncology (SIOP-) HARMONICA initiative review for pediatric renal tumors details germline genetic and epigenetic predisposition to BWT development, with an emphasis on alterations in 11p15.5 (ICR1 gain of methylation, paternal uniparental disomy, and postzygotic somatic mosaicism), WT1, TRIM28, and REST. Molecular mechanisms that result in BWT are often also present in multifocal Wilms tumor (multiple separate tumors in one or both kidneys). We identify priority areas for international collaborative research to better understand how predisposing genetic or epigenetic factors associate with response to neoadjuvant chemotherapy, oncologic outcomes, and long-term renal function outcomes.

An update on congenital melanocytic nevus syndrome: A case report and literature review

Congenital melanocytic nevus syndrome (CMNS) is a rare condition characterized by pigmented skin lesions that are usually present at birth and are associated with an increased risk of neurological abnormalities and malignant melanoma. It mostly results from a post-zygotic NRAS mutation of neural-derived crest cells, leading to uncontrolled cell growth. Because of the increased knowledge of the genetics underlying CMNS, targeted therapy becomes a promising treatment option. We present a case of CMNS in a newborn. Physical examination at birth showed a giant congenital melanocytic nevus, extending from the occipital to the lower lumbar region. A magnetic resonance imaging scan revealed multiple cerebral and cerebellar parenchymal lesions. Genetic analysis of the cutaneous lesions showed the presence of an NRAS Q61R mutation. The patient was treated with dermabrasion to reduce the color intensity of the nevus. However, this was complicated by recurrent wound infections and laborious wound healing. At the age of 1 year, the patient had an age-appropriate psychomotor development, without neurological deficits.