Heterozygous Mutations in OAS1 Cause Infantile-Onset Pulmonary Alveolar Proteinosis with Hypogammaglobulinemia

Abstract

Pulmonary alveolar proteinosis (PAP) is characterized by accumulation of a surfactant-like substance in alveolar spaces and hypoxemic respiratory failure. Genetic PAP (GPAP) is caused by mutations in genes encoding surfactant proteins or genes encoding a surfactant phospholipid transporter in alveolar type II epithelial cells. GPAP is also caused by mutations in genes whose products are implicated in surfactant catabolism in alveolar macrophages (AMs). We performed whole-exome sequence analysis in a family affected by infantile-onset PAP with hypogammaglobulinemia without causative mutations in genes associated with PAP: SFTPB, SFTPC, ABCA3, CSF2RA, CSF2RB, and GATA2. We identified a heterozygous missense variation in OAS1, encoding 2,'5'-oligoadenylate synthetase 1 (OAS1) in three affected siblings, but not in unaffected family members. Deep sequence analysis with next-generation sequencing indicated 3.81% mosaicism of this variant in DNA from their mother's peripheral blood leukocytes, suggesting that PAP observed in this family could be inherited as an autosomal-dominant trait from the mother. We identified two additional de novo heterozygous missense variations of OAS1 in two unrelated simplex individuals also manifesting infantile-onset PAP with hypogammaglobulinemia. PAP in the two simplex individuals resolved after hematopoietic stem cell transplantation, indicating that OAS1 dysfunction is associated with impaired surfactant catabolism due to the defects in AMs.

Keywords: 2′,5′-oligoadenylate synthetase 1; OAS1; PAP; alveolar macrophage; hypogammaglobulinemia; pulmonary alveolar proteinosis.

Figure 1

OAS1 Variants in Three Families with PAP and Evolutionary Conservation and Variations in OAS1 (A–C) Genetic analysis for OAS1 variation. Sanger sequencing demonstrated variations of (A) c.227C>T (p.Ala76Val) in family A, (B) c.326G>A (p.Cys109Tyr) in family B, and (C) c.592C>G (p.Leu198Val) in family C. Black arrows show the positions of the variations. (D) Schematic representation of OAS1 mutations. Black circles indicate the variants identified in this study. Blue and red triangles indicate metal binding sites (Asp75, Asp77, and Asp148) and ATP binding sites (Ser63, Lys213, and Gln229), respectively. Green and yellow boxes show the nucleotidyltransferase (NTP_transf_2) domain and 2′,5′-oligoadenylate synthetase 1, domain 2, and C terminus (OAS1_C) domain, respectively, predicted using the SMART program (see Web Resources). (E) Evolutionary conservation of Ala76, Cys109, and Leu198 amino acids in human OAS1. These amino acids are highlighted in green. Six orthologous sequences were aligned using the multiple sequence alignment program, Clustal Omega (see Web Resources).

Figure 2

Impact of the Identified Variants on Protein Structure (A) Mapping of the mutations on the crystal structures of a double-stranded RNA (dsRNA)-bound form of human oligoadenylate synthetase 1 (hOAS1) and an apo form of porcine OAS1 (pOAS1) (PDB: 4ig8 and 1px5, respectively). The superimposed structures of the dsRNA-bound (cyan) and apo (green) forms of OAS1 are presented as ribbon diagrams. The stick model is shown in gray. The altered residues are shown as van der Waals spheres in blue and dark green in the dsRNA-bound and apo forms, respectively. The substrate analog, 2′-deoxy ATP (dATP), and magnesium ions are shown as orange sticks and purple balls, respectively. Close-up views around the mutation sites are shown separately for the dsRNA-bound and apo forms. In the close-up views, some side chains of the hydrophobic residues around the mutation sites are shown as translucent spheres. (B) The free energy changes associated with each variant in a dsRNA-bound form of hOAS1 and apo form of pOAS1 by the FoldX software are shown.