Novel GUCY2C variant causing familial diarrhea in a Mennonite kindred and a potential therapeutic approach

Abstract

Guanylate cyclase 2C (GC‐C), encoded by the GUCY2C gene, is implicated in hereditary early onset chronic diarrhea. Several families with chronic diarrhea symptoms have been identified with autosomal dominant, gain‐of‐function mutations in GUCY2C. We have identified a Mennonite patient with a novel GUCY2C variant (c.2381A > T; p.Asp794Val) with chronic diarrhea and an extensive maternal family history of chronic diarrhea and bowel dilatation. Functional studies including co‐segregation analysis showed that all family members who were heterozygous for this variant had GI‐related symptoms. HEK‐293 T cells expressing the Asp794Val GC‐C variant showed increased cGMP production when stimulated with Escherichia coli heat‐stable enterotoxin STp (HST), which was reversed when 5‐(3‐Bromophenyl)‐5,11‐dihydro‐1,3‐dimethyl‐1H‐indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidine‐2,4,6(3H)‐trione (BPIPP; a GC‐C inhibitor) was used. In addition, cystic fibrosis transmembrane conductance regulator (CFTR) activity measured with SPQ fluorescence assay was increased in these cells after treatment with HST, indicating a crucial role for CFTR activity in the pathogenesis of this disorder. These results support pathogenicity of the GC‐C Asp794Val variant as a cause of chronic diarrhea in this family. Furthermore, this work identifies potential candidate drug, GC‐C inhibitor BPIPP, to treat diarrhea caused by this syndrome.

A Potential Treatment of Congenital Sodium Diarrhea in Patients With Activating GUCY2C Mutations

“…De novo GCC mutations that result in elevated constitutive GCC enzymatic activity and in abnormally increased sensitivity to stimulation by GCC ligands cause the severe and potentially lethal disease, CSD ( 7 ). Inherited GCC mutations that result in only increased ligand sensitivity cause a less severe diarrheal phenotype ( 6 , 8 ). We reported in this study a novel GCC mutation in a patient with PN-dependent CSD.…”

“…Two different classes of compounds that specifically inhibit GCC were developed, BPIPP ( 11 ) and SSP2518 ( 10 ), but no approved GCC-targeting treatments exist ( 4 ). BPIPP was recently shown to reverse the effect of the GCC mutation p.Asp794Val in vitro ( 8 ). We showed in this study that SSP2518-mediated inhibition of GCC normalizes the basal and stimulated levels of cGMP and significantly reduces CFTR-dependent chloride secretion in organoids with distinct GCC mutations.…”

“…One type of congenital enteropathy, the classical form of congenital sodium diarrhea (CSD), is caused by gain-of-function mutations in GUCY2C, encoding GCC (6)(7)(8), or by loss-offunction mutations in NHE3 (9). Such GCC mutations result in polyhydramnios and severe diarrhea from birth onward, generally requiring long-term parenteral nutrition (PN) (7).…”

Clinical course and therapeutic trial for a case of congenital secretory diarrhea due to novel GUCY2C variant

“…A limited number of activating variants have thus far been reported and confirmed via functional studies in the literature (Fiskerstrand et al, 2012;Muller et al, 2016;Wolfe et al, 2021). The variant identified in our patient is a novel de novo variant at a highly conserved residue that is nearby in linear sequence and the 3-dimensional crystal structure to several well-characterized gain-of-function variants confirmed utilizing Human Embryonic 293 (HEK-293) cells (Figure S1) (Fiskerstrand et al, 2012;Muller et al, 2016;Wolfe et al, 2021). Our patient's elevated stool chloride, sodium, and alkaline pH appear consistent with downstream actions of GC-C on CFTR and NHE3 which has been reported in several wellcharacterized GUCY2C variants (Muller et al, 2016).…”

“…Despite profuse diarrhea, activating variants also demonstrate overall delayed gut transit time with prominent dilation of bowel (von Volkmann et al, 2016;von Volkmann et al, 2017). A limited number of activating variants have thus far been reported and confirmed via functional studies in the literature (Fiskerstrand et al, 2012;Muller et al, 2016;Wolfe et al, 2021). The variant identified in our patient is a novel de novo variant at a highly conserved residue that is nearby in linear sequence and the 3-dimensional crystal structure to several well-characterized gain-of-function variants confirmed utilizing Human Embryonic 293 (HEK-293) cells (Figure S1) (Fiskerstrand et al, 2012;Muller et al, 2016;Wolfe et al, 2021).…”