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Legius syndrome, commonly referred to as SPRED1-related neurofibromatosis type 1-like syndrome, is a rare autosomal dominant disorder characterized by café-au-lait macules, freckling, lipomas, macrocephaly, and heterogeneous neurodevelopmental manifestations, including a different degree of learning difficulties. Although a partial clinical overlap exists with neurofibromatosis type 1 (NF1), Legius syndrome is distinguished by its genetic etiology and the absence of neurofibromas, indicating an inherent lack of tumor risk. The SPRED1 gene encodes the Sprouty-related protein with an EVH1 domain 1 (SPRED1), a negative regulator of the RAS-MAPK signaling pathway with a crucial role in cellular growth and development. Despite various genetic variants and genomic deletions associated with Legius syndrome, the full genetic spectrum of this condition remains elusive. In this study, we investigated the underlying genetic etiology in a cohort of patients presenting with typical manifestations of Legius syndrome using a custom Next Generation Sequencing (NGS) panel and Multiplex Ligation-Dependent Probe Amplification (MLPA) for NF1 and SPRED1. We identified 12 novel SPRED1 damaging variants segregating with the phenotype in all families. These rare variants affect conserved residues of the protein and are predicted damaging according to in silico tools. No clear genotype-phenotype correlations could be observed in the current cohort and previously reported patients, underscoring the heterogeneous genotype spectrum of this condition. Our findings expand the understanding of SPRED1 variants causing Legius syndrome and underscore the importance of comprehensively characterizing the genetic landscape of this disorder. Despite the absence of clear genotype-phenotype correlations, elucidating the genetic etiology of Legius syndrome is pertinent for facilitating accurate diagnosis, genetic counseling, and therapeutic interventions., (© 2024 The Author(s). American Journal of Medical Genetics Part A published by Wiley Periodicals LLC.)

Background : Plexiform neurofibromas (pNFs) are benign neoplasms, primarily originating from Schwann cells, posing challenges in patients with type 1 neurofibromatosis (NF1) due to pain, disfigurement, compression of vital structures and potential for malignancy. Selumetinib, a MEK1/2 inhibitor, has shown promising results in treating inoperable pNFs, with clinical trials demonstrating tumor volume reduction and improved patient-reported outcomes. Despite its efficacy, dermatologic toxicities may impact the quality of life and treatment adherence. Evaluating the frequency and spectrum of such effects is crucial for effective management. Methods : In a four-year retrospective and prospective study, pediatric NF1 patients with symptomatic, inoperable plexiform neurofibromas (pNFs) were treated with selumetinib. Eligibility criteria included significant morbidity, pNF size exceeding 3 cm or surgical inoperability, and performance status >70%. Hematological, liver, lung and cardiac assessments established baseline health. Selumetinib, orally administered at 25 mg/m 2 twice, was administered for two years unless a response warranting extension occurred. Cutaneous AEs were documented and graded by severity according to CTCAE v5.0, with evaluations every three to six months. The impact on symptoms and pNF size was systematically recorded, and biopsies characterized histopathological features in those patients requiring surgery. Results : Twenty patients were enrolled, with an average age at therapy initiation of 11.6 years. Cutaneous side effects were common, with all patients experiencing at least one and a median of two per patient. Xerosis, paronychia and acneiform rash were prevalent. Notably, pre-pubertal individuals were more susceptible to xerosis. Acneiform rash had a higher incidence in older patients and those with skin phototypes II and III. Successful management involved tailored approaches, such as clindamycin for acneiform rash and topical agents for paronychia. Hair abnormalities, including color changes and thinning, occurred, with female patients at higher risk for the latter. Paronychia presented challenges, necessitating various interventions, including surgical approaches. AEs led to treatment suspension in 20% of patients, with tumor rebound observed in 75%. Conclusions : According to our experience, successful management of selumetinib-induced cutaneous AEs requires tailored strategies including surgery. AEs might indirectly determine pNF regrowth due to therapy suspension. We thus emphasize the pivotal role of addressing cutaneous reactions for effective selumetinib management in pediatric patients., Competing Interests: The authors declare no conflicts of interest.