Waardenburg syndrome: Novel mutations in a large Brazilian sample

Abstract

This paper deals with the molecular investigation of Waardenburg syndrome (WS) in a sample of 49 clinically diagnosed probands (most from southeastern Brazil), 24 of them having the type 1 (WS1) variant (10 familial and 14 isolated cases) and 25 being affected by the type 2 (WS2) variant (five familial and 20 isolated cases). Sequential Sanger sequencing of all coding exons of PAX3, MITF, EDN3, EDNRB, SOX10 and SNAI2 genes, followed by CNV detection by MLPA of PAX3, MITF and SOX10 genes in selected cases revealed many novel pathogenic variants. Molecular screening, performed in all patients, revealed 19 causative variants (19/49 = 38.8%), six of them being large whole-exon deletions detected by MLPA, seven (four missense and three nonsense substitutions) resulting from single nucleotide substitutions (SNV), and six representing small indels. A pair of dizygotic affected female twins presented the c.430delC variant in SOX10, but the mutation, imputed to gonadal mosaicism, was not found in their unaffected parents. At least 10 novel causative mutations, described in this paper, were found in this Brazilian sample. Copy-number-variation detected by MLPA identified the causative mutation in 12.2% of our cases, corresponding to 31.6% of all causative mutations. In the majority of cases, the deletions were sporadic, since they were not present in the parents of isolated cases. Our results, as a whole, reinforce the fact that the screening of copy-number-variants by MLPA is a powerful tool to identify the molecular cause in WS patients.

Biology of human melanocyte development, Piebaldism, and Waardenburg syndrome

“…The majority (> 60%) of WS2 cases are unexplained at the molecular level . Heterozygous MITF and SOX10 mutations each account for 15% of cases; SNAI2, EDNRB , and KITLG are rare and account for less than 5% . Proteins that activate or repress the expression of MITF‐M are potential gene candidates.…”

“…97 Heterozygous MITF and SOX10 mutations each account for 15% of cases; SNAI2, EDNRB, and KITLG are rare and account for less than 5%. 98,99 Proteins that activate or repress the expression of MITF-M are potential gene candidates. For instance, FOXD3, POU3F2, ALX3, TNF-α, and TGF-ß can reduce MITF-M levels; in contrast, genes involved in cAMP-CREB, Wnt, or MAPK signaling pathways can increase MITF expression.…”

Sequenciamento de nova geração e sua aplicação no estudo genético da síndrome de Waardenburg

“…(BERTOLOTTO et al, 1998;PINGAULT et al, 2010;TACHIBANA et al, 1996;TASSABEHJI;READ, 1994;YASUMOTO et al, 1994). (BOCÁNGEL et al, 2018;BONDURAND et al, 2007;FALAH et al, 2017;HEMMI et al, 2018;LI et al, 2019;STEVENSON et al, 2018). (2015) analisaram pacientes SW2 pesquisando mutações em KITLG e descreveram uma mutação em heterozigose fortemente candidata a explicar um caso familial de SW2.…”

“…Na SW2, tipo com menor taxa de detecção, explicam o quadro 15% das variantes patogênicas em MITF, 15% em SOX10, 5-6% em EDNRB e um valor pouco expressivo de alterações em KITLG e SNAI2 (único por mecanismo recessivo), somando então menos de 50% de detecção para o tipo 2 (BARAL et al, 2012;BONDURAND et al, 2007;ISSA et al, 2017;PINGAULT et al, 2010;READ;NEWTON, 1997;ZAZO SECO et al, 2015). São também causa da SW2, ainda que pouco expressivas, variações no número de cópias dos genes MITF e SOX10 (BOCÁNGEL et al, 2018;BONDURAND et al, 2007;HEMMI et al, 2018;LI et al, 2019;MILUNSKY et al, 2007;WILDHARDT et al, 2013). Duas variantes intrônicas no gene MITF foram relacionadas também à SW2, uma delas tanto em homozigose quanto em heterozigose (HADDAD et al, 2011;RAUSCHENDORF et al, 2019).…”

“…SW3, o que evidencia que mutações muito próximas podem levar a quadros clínicos distintos(HOTH et al, 1993). Estudos relacionados à detecção molecular da SW por meio da análise de variantes de número de cópias revelaram que deleções totais ou parciais do gene PAX3 contribuem com 10% dos diagnósticos moleculares quando não são encontradas variantes de ponto pela técnica de sequenciamento convencional em indivíduos clinicamente diagnosticados com SW1 ou SW3, sem que haja uma diferença na gravidade clínica entre pacientes portadores de deleções totais ou parciais(BOCÁNGEL et al, 2018; MILUNSKY, 2006 apud MILUNSKY et al, (2007MILUNSKY et al, 2007;WILDHARDT et al, 2013).…”