NGS Gene Panel Analysis Revealed Novel Mutations in Patients with Rare Congenital Diarrheal Disorders

Three patients with new mutations in the EPCAM variant gene for congenital tufting enteropathy and a mutation review in China: a case report

Background

Congenital tufting enteropathy (CTE) is a rare cause of intractable congenital diarrhea in children, always resulting in parenteral nutrition (PN) dependency. We aimed to report novel mutations in Chinese patients and to illustrate the clinical, histopathological, and molecular features of CTE in China.

Case Description

We report three cases of CTE diagnosed with whole-exome sequencing (WES) and MOC31 [a monoclonal antibody of epithelial cell adhesion molecule (EPCAM)] immunohistochemistry. The main manifestations in the three patients were watery diarrhea and growth retardation. Upper endoscopy in three patients revealed villous atrophy of the duodenal mucosa. Histological examination revealed villus abnormalities and two patients with focal tufting. All of the three patients revealed a complete absence of EPCAM expression through MOC31 immunohistochemistry. Five novel mutations, including c.319delG, c.505_507delGAG, c.491+1G>C, c.60del (p.F20Lfs*17), and c.353G>A, in EPCAM were identified through molecular analysis. In our review, there were 18 different mutations in 11 patients from nine studies, with 12 mutations reported only once. In China, 73% of the patients were compound heterozygotes, and most of the pathogenic variants were in exon 3. All patients presented with congenital diarrhea and needed PN because of growth retardation, even when diarrhea was improved. Of the 11 patients, 3 (27%) died.

Conclusions

CTE is rare and fatal, and lacks characteristic changes during endoscopy. Patients with CTE require early diagnosis via histological examination and genetic detection to improve survival.

Nonsense mutation in the novel PERCC1 gene as a genetic cause of congenital diarrhea and enteropathy

Congenital diarrheas and enteropathies (CODEs) constitute a heterogeneous group of individually rare disorders manifesting with infantile-onset chronic diarrhea. Genomic deletions in chromosome 16, encompassing a sequence termed the 'intestine-critical region (ICR)', were recently identified as the cause of an autosomal recessive congenital enteropathy. The regulatory sequence within the ICR is flanked by an unannotated open reading frame termed PERCC1, which plays a role in enteroendocrine cell (EEC) function. We investigated two unrelated children with idiopathic congenital diarrhea requiring home parenteral nutrition attending the Irish Intestinal Failure Program. Currently 12 and 19-years old, these Irish male patients presented with watery diarrhea and hypernatremic dehydration in infancy. Probands were phenotyped by comprehensive clinical investigations, including endoscopic biopsies and serum gastrin level measurements. Following negative exome sequencing, PCR and Sanger sequencing of the entire coding region and intron boundaries of PERCC1 were performed for each proband and their parents. In both patients, serum gastrin levels were low and failed to increase following a meal challenge. While no deletions involving the ICR were detected, targeted sequencing of the PERCC1 gene revealed a shared homozygous c.390C > G stop gain variant. We report clinical and molecular findings in two unrelated patients harboring a shared homozygous variant in PERCC1, comprising the first description of a point mutation in this gene in association with CODE. That both parenteral nutrition dependent children with unexplained diarrhea at our institution harbored a PERCC1 mutation underscores the importance of its inclusion in exome sequencing interpretation.

UNC45A-related osteo-oto-hepato-enteric syndrome in a Chinese neonate

Unexplained diarrhea and cholestasis are common clinical phenotypes in newborns, indicating there is only a little common genetic basis for these conditions. However, it has been reported that defects in the UNC45A gene can lead to osteo-oto-hepato-enteric syndrome. However, to date, only 10 patients with this syndrome have been reported in 2 studies; therefore, there is still a lack of analysis regarding the correlation between disease phenotype and genotype. Trio-whole exome sequencing was conducted using DNA samples from a newborn with congenital diarrhea and cholestasis from a Chinese Han family. The UNC45A variants were verified using Sanger sequencing. In addition, we applied a crystal structure model to analyze the potential hazards associated with the variants. The plasmids were constructed in vitro and transfected into human 293T cells for Western blot (WB) analysis. After the mutant protein was fused with the Green Fluorescent Protein label, intracellular localization was observed using laser confocal microscopy. The gene detection results showed that the UNC45A gene of the newborn examined in the present study harbored the compound heterozygous variants p.Arg819Ter, and p.Leu237Pro; this was confirmed via Sanger sequencing. Analysis of the Leu237Pro crystal structure model suggested that this variant may decrease local structural stability and affect protein function. The Western blot and laser confocal microscopy observation results suggested that the Leu237Pro mutation leads to reduced protein expression, while the Arg819Ter mutation completely inhibits the expression of the protein. The compound heterozygous variants of UNC45A (p.Arg819Ter and p.Leu237Pro) may be pathogenic factors of congenital diarrhea and cholestasis in this neonatal patient. Therefore, UNC45A deficiency should be considered when intractable diarrhea and cholestasis occur in newborns.