Functional validation of novel MKS3/TMEM67 mutations in COACH syndrome

So-Hyun Lee,Myeong-Kyu Kim,Jung Ha Kim,Nacksung Kim,Yoo-Duk Choi,Kee Oh Chay,Min Jung Kim,Hua Cai,Tai-Seung Nam,Changsoo Kim,Kun-Hee Kim,Seok-Yong Choi,Wenting Li,Woong Yoon,Hyon E Choy

doi:10.1038/s41598-017-10652-z

So-Hyun Lee, Myeong-Kyu Kim + Show 13 more

Open Access

https://doi.org/10.1038/s41598-017-10652-z

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Abstract

COACH syndrome is an autosomal recessive developmental disorder, a subtype of Joubert syndrome and related disorders, characterized by cerebellar vermis hypoplasia, oligophrenia, ataxia, coloboma, and hepatic fibrosis. Although mutations in TMEM67 (transmembrane protein 67)/MKS3 (Meckel-Gruber syndrome, type 3) were reported to cause COACH syndrome, this causality has not verified by functional studies. In a 20-year-old Korean man, we found cerebellar ataxia, isolated elevation in serum γ-glutamyl transpeptidase (γ-GTP) activity, oligophrenia, the molar tooth sign (MTS) in the brain MR images and congenital hepatic fibrosis (CHF). Two novel compound heterozygous mutations were found in TMEM67 in the patient: i) missense mutation (c.395 G > C and p.Gly132Ala) in exon 3, and ii) deletion in exon 26 (c.2758delT and p.Tyr920ThrfsX40). Western blotting showed that the p.Tyr920ThrfsX40 mutation accelerates turnover of the TMEM67 protein. Although wild-type human TMEM67 RNA rescued phenotypes of zebrafish embryos injected with anti-sense oligonucleotide morpholinos against tmem67, the two human TMEM67 RNAs individually harboring the two mutations did not. Finally, Wnt signaling, but not Hedgehog signaling, was suppressed in tmem67 morphants. To the best of our knowledge, this is the first report verifying the causality between COACH syndrome and TMEM67, which will further our understanding of molecular pathogenesis of the syndrome.

Highlights

Joubert syndrome (JBTS), first described in 1969 by Joubert and colleagues[1], is a rare neurodevelopmental disorder with a complex mid-hindbrain malformation characterized by the “molar tooth sign” (MTS) on axial brain magnetic resonance (MR) images[2, 3]
Korean Mini-Mental Status Examination (K-MMSE) was performed and the score was 29, which is within normal limits
What is the molecular mechanism by which mutations in the same gene cause various genetic diseases? Physical location of the mutations in the Transmembrane Protein 67 gene (TMEM67) protein may not account for the difference in phenotypes based on the following reasons

Summary

Introduction

Joubert syndrome (JBTS), first described in 1969 by Joubert and colleagues[1], is a rare neurodevelopmental disorder with a complex mid-hindbrain malformation characterized by the “molar tooth sign” (MTS) on axial brain magnetic resonance (MR) images[2, 3]. One type of JSRD with neurological signs of JBTS and congenital hepatic fibrosis (CHF) is called the COACH syndrome (Cerebellar vermis hypoplasia, Oligophrenia, Ataxia, Coloboma, and Hepatic fibrosis; Online Mendelian Inheritance in Man [OMIM] # 216360)[3, 5, 6]. Human TMEM67 has 995 amino acid residues and harbors four kinds of domains: a signal peptide, a cysteine-rich repeat region, three transmembrane domains and a coiled-coil domain, from N- to C-terminus (Fig. 1a)[11, 12]. Mutations were identified throughout the TMEM67 gene in COACH syndrome patients[7]. We report two novel mutations (p.Gly132Ala and p.Tyr920ThrfsX40) in TMEM67 in a Korean patient with clinical manifestations of JBTS and CHF

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