Mosaic BRAF fusions are a recurrent cause of congenital melanocytic naevi targetable by MEK inhibition

Among children with multiple congenital melanocytic naevi (CMN), 25% have no established genetic cause, of which many develop a hyperproliferative and severely pruritic phenotype resistant to treatment. Gene fusions have been reported in individual cases of CMN. Here, we study 169 CMN patients, 38 of whom were double wild-type for NRAS/BRAF mutations. Nineteen of these 38 patients had sufficient tissue to undergo RNAseq, which revealed mosaic BRAF fusions in 11/19 patients and mosaic RAF1 fusions in 1/19. Recurrently, fusions involved the loss of the 5’ regulatory domain of BRAF or RAF1 but preserved the kinase domain. We validated all cases and detected the fusions in two separate naevi in 5/12 patients, confirming clonality. The absence of the fusion in blood in 8/12 patients indicated mosaicism. Primary culture of BRAF-fusion naevus cells from 3/12 patients demonstrated highly increased MAPK activation, despite only mildly increased BRAF expression, suggesting additional mechanisms of kinase activation. Trametinib quenched MAPK hyperactivation in vitro and treatment of two patients caused rapid improvement in bulk tissue, improving bodily movement, and reducing inflammation and severe pruritus. These findings offer a genetic diagnosis to an additional group of patients and trametinib as a treatment option for the severe associated phenotypes

Clinical spectrum of MTOR-related hypomelanosis of Ito with neurodevelopmental abnormalities.

PURPOSE: Hypomelanosis of Ito (HI) is a skin marker of somatic mosaicism. Mosaic MTOR pathogenic variants have been reported in HI with brain overgrowth. We sought to delineate further the pigmentary skin phenotype and clinical spectrum of neurodevelopmental manifestations of MTOR-related HI. METHODS: From two cohorts totaling 71 patients with pigmentary mosaicism, we identified 14 patients with Blaschko-linear and one with flag-like pigmentation abnormalities, psychomotor impairment or seizures, and a postzygotic MTOR variant in skin. Patient records, including brain magnetic resonance image (MRI) were reviewed. Immunostaining (n = 3) for melanocyte markers and ultrastructural studies (n = 2) were performed on skin biopsies. RESULTS: MTOR variants were present in skin, but absent from blood in half of cases. In a patient (p.[Glu2419Lys] variant), phosphorylation of p70S6K was constitutively increased. In hypopigmented skin of two patients, we found a decrease in stage 4 melanosomes in melanocytes and keratinocytes. Most patients (80%) had macrocephaly or (hemi)megalencephaly on MRI. CONCLUSION: MTOR-related HI is a recognizable neurocutaneous phenotype of patterned dyspigmentation, epilepsy, intellectual deficiency, and brain overgrowth, and a distinct subtype of hypomelanosis related to somatic mosaicism. Hypopigmentation may be due to a defect in melanogenesis, through mTORC1 activation, similar to hypochromic patches in tuberous sclerosis complex

Understanding the Molecular and Genetic Basis of Complex Syndromes of Diabetes Mellitus

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A novel 3' untranslated region mutation in the SLC29A3 gene associated with pigmentary hypertrichosis and non-autoimmune insulin-dependent diabetes mellitus syndrome.

BackgroundPigmentary hypertrichosis and non-autoimmune insulin-dependent diabetes mellitus (PHID) is one of the rare H syndrome diseases mainly characterized by hyperpigmentation, hypertrichosis, sensorineural hearing loss, cardiac complications, developmental delay, and diabetes mellitus (DM). Mutations in the coding regions of the SLC29A3 gene that encodes for an equilibrative nucleoside transporter (ENT3) have been reported to cause the phenotypic spectrum of the H syndrome. Disease-causing mutations in the untranslated regions (UTRs) of the SLC29A3 gene have not been previously described in the literature. The aim of the study is to describe and assess the pathogenicity of a novel 3'UTR mutation in the SLC29A3 gene associated with the PHID phenotype in two Turkish patients

Functional assessment of variants associated with Wolfram syndrome

Wolfram Syndrome (WS) is a heterogeneous multisystem neurodegenerative disorder with two allelic variations in addition to a separate subtype known as WS type 2. The wide phenotypic spectrum of WS includes diabetes mellitus and optic atrophy which is often accompanied by diabetes insipidus, deafness, urological and neurological complications in combination or in isolation. To date, the understanding of the genotype phenotype relationship in this complex syndrome remains poorly understood. In this study we identified and explored the functionality of rare and novel variants in the two causative WS genes WFS1 and CISD2 by assessing the effects of the mutations on the encoded proteins Wolframin and ERIS, in a cohort of 12 patients with autosomal recessive WS, dominant WS and WS type 2. The identified pathogenic variants included missense changes, frameshift deletions and insertions in WFS1 and an exonic deletion in CISD2 which all altered the respective encoded protein in a manner that did not correlate to the phenome previously described. These observations suggest the lack of genotype phenotype correlation in this complex syndrome and the need to explore other molecular genetic mechanisms. Additionally, our findings highlight the importance of functionally assessing variants for their pathogenicity to tackle the problem of increasing variants of unknown significance (VUS) in the public genetic databases

Mosaic BRAF fusions are a recurrent cause of congenital melanocytic naevi targetable by MEK pathway inhibition.

Among children with multiple congenital melanocytic naevi (CMN), 25% have no established genetic cause, of which many develop a hyperproliferative and severely pruritic phenotype resistant to treatment. Gene fusions have been reported in individual cases of CMN. Here, we study 169 CMN patients, 38 of whom were double wild-type for NRAS/BRAF mutations. Nineteen of these 38 patients had sufficient tissue to undergo RNAseq, which revealed mosaic BRAF fusions in 11/19 patients and mosaic RAF1 fusions in 1/19. Recurrently, fusions involved the loss of the 5' regulatory domain of BRAF or RAF1 but preserved the kinase domain. We validated all cases and detected the fusions in two separate naevi in 5/12 patients, confirming clonality. The absence of the fusion in blood in 8/12 patients indicated mosaicism. Primary culture of BRAF-fusion naevus cells from 3/12 patients demonstrated highly increased MAPK activation, despite only mildly increased BRAF expression, suggesting additional mechanisms of kinase activation. Trametinib quenched MAPK hyperactivation in vitro and treatment of two patients caused rapid improvement in bulk tissue, improving bodily movement, and reducing inflammation and severe pruritus. These findings offer a genetic diagnosis to an additional group of patients and trametinib as a treatment option for the severe associated phenotypes

Correction to: Clinical spectrum of MTOR-related hypomelanosis of Ito with neurodevelopmental abnormalities

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