Pathogenic STX3 variants affecting the retinal and intestinal transcripts cause an early-onset severe retinal dystrophy in microvillus inclusion disease subjects

Andreas R Janecke,Rüdiger Adam,Xiaoqin Liu,Valeria Strauß,Thomas Müller,Elizabeth Sánchez ,Klaus Rohrschneider,Naveen K Mittal ,Badr Alsaleem,Martha Schatz ,Siham Al-Sinani ,Ruth Heidelberger,Johanna C Escher ,Majid Alfadhel,Anuradha Ganesh,Fathiya Al Murshedi,Sumanth Punuru,Sana Al Zuhaibi,Ujwala S Saboo,Fowzan S Alkuraya,Martin W Laaß ,Roberto Adachi,Arne Viestenz,Lukas A Huber,Roger Janz

doi:10.1007/s00439-021-02284-1

Abstract

Biallelic STX3 variants were previously reported in five individuals with the severe congenital enteropathy, microvillus inclusion disease (MVID). Here, we provide a significant extension of the phenotypic spectrum caused by STX3 variants. We report ten individuals of diverse geographic origin with biallelic STX3 loss-of-function variants, identified through exome sequencing, single-nucleotide polymorphism array-based homozygosity mapping, and international collaboration. The evaluated individuals all presented with MVID. Eight individuals also displayed early-onset severe retinal dystrophy, i.e., syndromic—intestinal and retinal—disease. These individuals harbored STX3 variants that affected both the retinal and intestinal STX3 transcripts, whereas STX3 variants affected only the intestinal transcript in individuals with solitary MVID. That STX3 is essential for retinal photoreceptor survival was confirmed by the creation of a rod photoreceptor-specific STX3 knockout mouse model which revealed a time-dependent reduction in the number of rod photoreceptors, thinning of the outer nuclear layer, and the eventual loss of both rod and cone photoreceptors. Together, our results provide a link between STX3 loss-of-function variants and a human retinal dystrophy. Depending on the genomic site of a human loss-of-function STX3 variant, it can cause MVID, the novel intestinal-retinal syndrome reported here or, hypothetically, an isolated retinal dystrophy.

Highlights

A severe form of hereditary diarrhea called microvillus inclusion disease (MVID, OMIM 251850) (Vogel et al 2016) was described in five individuals with biallelic mutations of the syntaxin 3 gene (STX3, OMIM 600876) by us and by others (Alsaleem et al 2017; Julia et al 2019; Wiegerinck et al 2014)
Given that our mRNA expression analysis of human retina showed that STX3A corresponds to only about 1% of total STX3 mRNA (Fig. 1m), the observed STX3 signal in human retina most likely corresponds almost exclusively to STX3B, as it does in the mouse retina (Curtis et al 2008)
We report here that individuals with MVID and with biallelic STX3 loss-of-function variants that affect both STX3A and STX3B transcript isoforms display visual impairment consistent with an early-onset severe retinal dystrophy (EOSRD)

Summary

Introduction

A severe form of hereditary diarrhea called microvillus inclusion disease (MVID, OMIM 251850) (Vogel et al 2016) was described in five individuals with biallelic mutations of the syntaxin 3 gene (STX3, OMIM 600876) by us and by others (Alsaleem et al 2017; Julia et al 2019; Wiegerinck et al 2014). STX3 is required for the proper trafficking of vesicles to and fusion with the apical membrane in mammalian epithelial cells (Low et al 1998; Vogel et al 2015) indicating that the lack of STX3A in epithelial cells causes MVID. We have characterized another transcript, syntaxin 3B, generated by differential splicing and highly expressed in the retinas of mice and fish, where syntaxin 3A mRNA is only expressed at very low levels (Curtis et al 2008, 2010). Our study demonstrates that STX3 is essential for the function of the mammalian retina and that human variants affecting STX3B are associated with retinal dysfunction

Materials and methods

Discussion

Findings

Data and code availability