Hypomorphic splice site IL2RG variants associated with Cryptosporidium liver disease

Abstract

BackgroundX-linked severe combined immunodeficiency (X-SCID) is caused by mutations in IL2RG encoding for the common gamma chain (γc). This disease is typically fatal within the first year without immune reconstitution. We present two patients with IL2RG variants leading to a phenotype of Cryptosporidium-related sclerosing cholangitis. MethodsMedical history and laboratories were reviewed for two patients with IL2RG variants at c.270G. For one patient, we examined cDNA, γc expression, TCR repertoire, cytokine signaling, in vitro B-cell plasmablast differentiation, and in vitro T-cell differentiation of peripheral blood CD34+ cells. ResultsTwo unrelated male patients (17 and 21 years old) were identified with liver disease, recurrent childhood pneumonia and resultant bronchiectasis. P1 has persistent warts. Elevated transaminases in P1 led to liver imaging and biopsy consistent with sclerosing cholangitis. Stool PCR was positive for Cryptosporidium. P2 was diagnosed at age 6 with cryptogenic cirrhosis. He underwent orthotopic liver transplant at age 19; diarrhea and cholestatic liver disease developed 4 months post-transplant, and cryptosporidium was found in stool and liver. Cryptococcus meningitis also developed on immunosuppression. Both patients were hemizygous for an IL2RG variant resulting in p.W90C (P1:c.270G>T; P2:c.270G>C). P1 had mildly reduced CD4+ lymphocytes, CD4+ and CD8+ central/ effector memory T-lymphocytes, memory B-lymphocytes, and normal NK counts. P1 cDNA revealed a leaky splicing defect with a mix of exons 2–4 skipping along with full-length transcript encoding p.W90C. Cells from heterozygous mother expressed wild-type sequence suggesting skewed X-inactivation. Surface protein expression and distribution of TCR V-Beta repertoire was largely normal. IL-2-mediated STAT5 phosphorylation was impaired in T- and NK-cells. P1’s B-lymphocytes proliferated in response to in vitro IL-21/CD40L co-stimulation but failed to differentiate into CD27+CD38+ plasmablasts (< 1%). In vitro T-cell differentiation showed impaired survival of developing thymocytes, despite capability of maturing intoTCRaB+ CD3+ T cells. ConclusionsWe present two patients hemizygous for IL2RG variants leading to milder clinical phenotype compared to classic X-SCID. Consistent with other diseases of impaired IL-21 signaling, there was significant Cryptosporidium-related liver disease in addition to clinical manifestations of hypomorphic IL-2 signaling defect. Further work is necessary to address restoring IL-21 signaling to improve liver disease.