A Hereditary Enteropathy Caused by Mutations in the <i>SLCO2A1</i> Gene, Encoding a Prostaglandin Transporter

<div><p>Previously, we proposed a rare autosomal recessive inherited enteropathy characterized by persistent blood and protein loss from the small intestine as chronic nonspecific multiple ulcers of the small intestine (CNSU). By whole-exome sequencing in five Japanese patients with CNSU and one unaffected individual, we found four candidate mutations in the <i>SLCO2A1</i> gene, encoding a prostaglandin transporter. The pathogenicity of the mutations was supported by segregation analysis and genotyping data in controls. By Sanger sequencing of the coding regions, 11 of 12 other CNSU patients and 2 of 603 patients with a diagnosis of Crohn’s disease were found to have homozygous or compound heterozygous <i>SLCO2A1</i> mutations. In total, we identified recessive <i>SLCO2A1</i> mutations located at seven sites. Using RT-PCR, we demonstrated that the identified splice-site mutations altered the RNA splicing, and introduced a premature stop codon. Tracer prostaglandin E2 uptake analysis showed that the mutant SLCO2A1 protein for each mutation exhibited impaired prostaglandin transport. Immunohistochemistry and immunofluorescence analyses revealed that SLCO2A1 protein was expressed on the cellular membrane of vascular endothelial cells in the small intestinal mucosa in control subjects, but was not detected in affected individuals. These findings indicate that loss-of-function mutations in the <i>SLCO2A1</i> gene encoding a prostaglandin transporter cause the hereditary enteropathy CNSU. We suggest a more appropriate nomenclature of “chronic enteropathy associated with <i>SLCO2A1</i> gene” (CEAS).</p></div

Pedigrees of the families with chronic nonspecific multiple ulcers of the small intestine.

<p>The segregation of the <i>SLCO2A1</i> mutations c.1461+1G>C (splice site, family A), c.940+1G>A (splice site, families B and C), c.664G>A (G222R, family D), and c.1807C>T (R603X, family D) is indicated. Squares represent male family members, circles represent female family members, black symbols represent clinically affected family members, and slashes represent deceased family members. Arrows indicate individuals whose DNA was analyzed by whole-exome sequencing. WT denotes wild-type.</p

Clinical images of an individual with chronic nonspecific multiple ulcers of the small intestine (patient A-V–2).

<p>(A, B) Retrograde ileoscopy shows active circular and oblique multiple ulcers with mucous exudates in the ileum. (C, D) A barium follow-through examination with compression shows multiple circular barium flecks (C), eccentric deformities, and strictures (D) in the ileum. (E, F) Radiographs of the hands and tibiofibulae show no obvious abnormalities such as cortical thickening of the metacarpals and periosteal hyperostosis.</p

Genetic and functional analyses of <i>SLCO2A1</i> gene mutations.

<p>(A) RT-PCR and sequencing analysis of <i>SLCO2A1</i> mRNA with homozygous c.940+1G>A mutation. A splicing mutation form (deletion of the whole exon 7) of <i>SLCO2A1</i> mRNA was expressed in the biopsy specimen from the affected siblings with the homozygous c.940+1G>A mutation (patients 6 and 7). PBMCs denotes peripheral blood mononuclear cells. (B) The mutant SLCO2A1 protein shows loss-of-function for PGE2 transport. Data represent means ± SD (<i>n</i> = 3). Statistical analyses were performed using a repeated-measures Dunnett’s multiple-comparison test. *<i>p</i> < 0.0001. (C) Immunohistochemical and immunofluorescence staining using antibodies against SLCO2A1 and VE-cadherin reveals that SLCO2A1 is expressed on the cellular membrane of vascular endothelial cells in the small intestinal mucosa in the control subject, but is not detected in the affected individuals. (D) The truncated form of the SLCO2A1 protein shows altered intracellular localization. Expression vectors for GFP-SLCO2A1 and GFP-ΔSLCO2A1 fusion proteins were transfected into HEK293 cells. GFP-SLCO2A1 protein is localized on the cellular membrane (arrows), while GFP-ΔSLCO2A1 accumulates in the cytosol.</p