Recurrent Mutations in the Basic Domain of TWIST2 Cause Ablepharon Macrostomia and Barber-Say Syndromes

Abstract

Ablepharon macrostomia syndrome (AMS) and Barber-Say syndrome (BSS) are rare congenital ectodermal dysplasias characterized by similar clinical features. To establish the genetic basis of AMS and BSS, we performed extensive clinical phenotyping, whole exome and candidate gene sequencing, and functional validations. We identified a recurrent de novo mutation in TWIST2 in seven independent AMS-affected families, as well as another recurrent de novo mutation affecting the same amino acid in ten independent BSS-affected families. Moreover, a genotype-phenotype correlation was observed, because the two syndromes differed based solely upon the nature of the substituting amino acid: a lysine at TWIST2 residue 75 resulted in AMS, whereas a glutamine or alanine yielded BSS. TWIST2 encodes a basic helix-loop-helix transcription factor that regulates the development of mesenchymal tissues. All identified mutations fell in the basic domain of TWIST2 and altered the DNA-binding pattern of Flag-TWIST2 in HeLa cells. Comparison of wild-type and mutant TWIST2 expressed in zebrafish identified abnormal developmental phenotypes and widespread transcriptome changes. Our results suggest that autosomal-dominant TWIST2 mutations cause AMS or BSS by inducing protean effects on the transcription factor's DNA binding.

Barber–Say syndrome and Ablepharon–Macrostomia syndrome: An overview

“…Gorlin et al [1990] suggested BSS and AMS to be allelic entities due to the substantial phenotypic overlap. This was confirmed by an international collaborative study as it demonstrated that both disorders can be caused by heterozygous mutations in TWIST2 [Marchegiani et al, 2015]. TWIST2 is located at 2q37.3, encodes for a bHLH protein that binds to E-box DNA motifs as a heterodimer with other similar proteins, and is considered to act as a negative regulator of transcription.…”

“…The term ablepharon is therefore in fact a misnomer, but for historical reasons we suggest to keep the term AMS unchanged. The anterior parts of the eyelids vary in their underdevelopment from being extremely small in AMS to minor reduction in size in BSS, to even less marked expression in a coloboma in a mosaic patient and absence of eyelashes only of the medially lower lid [Marchegiani et al, 2015]. The underdeveloped anterior lamella causes ectropion, causing in turn lagophtalmus, which may need surgical correction [McCarthy and West, 1977;David et al, 1991;Price et al, 1991;Cruz et al, 1995;Ferraz et al, 2000;Stevens and Sargent, 2002;Brancati et al, 2004;Martins et al, 2010;Roche et al, 2010;Rohena et al, 2011;Feinstein et al, 2015;Marchegiani et al, 2015].…”

“…The occurrence in two generations suggested autosomal dominant inheritance [Dinulos and Pagon, 1999;Roche et al, 2010]. In total 19 patients have been published as having BSS [Barber et al, 1982;David et al, 1991;Martinez Santana et al, 1993;Sod et al, 1997;Mazzanti et al, 1998;Dinulos and Pagon, 1999;Cort es et al, 2000;Ng and Rajguru, 2006;Tenea and Jacyk, 2006;Haensel et al, 2009;Martins et al, 2010;Roche et al, 2010;Suga et al, 2014;Marchegiani et al, 2015;Singh et al, 2016].…”

“…TWIST2 regulates mesenchymal stem cell differentiation and influences chondrogenic and dermal tissues. The authors suggested that TWIST2 mutations alter DNA-binding activity of TWIST2, and, thus, can have a dominant-negative and a gain-of-function effect [Marchegiani et al, 2015]. All 10 patients with AMS had the same E75K missense mutation in TWIST2, and the 11 patients with BSS had one of two missense mutations, both also involving codon 75 (E75Q and E75A), and 1 patient had a 6-bp duplication at codons 77 and 78.…”

Barber-Say Syndrome and Ablepharon-Macrostomia Syndrome: A Patient's View

“…The authors of 13 publications responded. Three BSS individuals [Barber et al, 1982;Dinulos and Pagon, 1999;Tenea and Jacyk, 2006] and 1 AMS individual [Stevens and Sargent, 2002] were lost to followup, so we gathered questionnaires from 10 BSS individuals and 2 AMS individuals [David et al, 1991;Mazzanti et al, 1998;Stevens and Sargent, 2002;Brancati et al, 2004;Haensel et al, 2009;Martins et al, 2010;Roche et al, 2010;Marchegiani et al, 2015;Singh et al, 2016]. The questionnaire was written in English, and in case a participant was unable to read and write English, local persons acted as interpreters.…”