A missense mutation in pstpip2 is associated with the murine autoinflammatory disorder chronic multifocal osteomyelitis

Abstract

Chronic recurrent multifocal osteomyelitis (CRMO) is an autoinflammatory disorder that primarily affects bone but is often accompanied by inflammation of the skin and/or gastrointestinal tract. The etiology is unknown but evidence suggests a genetic component to disease susceptibility. Although most cases of CRMO are sporadic, there is an autosomal recessive syndromic form of the disease, called Majeed syndrome, which is due to homozygous mutations in LPIN2. In addition, there is a phenotypically similar mouse, called cmo (chronic multifocal osteomyelitis) in which the disease is inherited as an autosomal recessive disorder. The cmo locus has been mapped to murine chromosome 18. In this report, we describe phenotypic abnormalities in the cmo mouse that include bone, cartilage and skin inflammation. Utilizing a backcross breeding strategy, we refined the cmo locus to a 1.3 Mb region on murine chromosome 18. Within the refined region was the gene pstpip2, which shares significant sequence homology to the PSTPIP1. Mutations in PSTPIP1 have been shown to cause the autoinflammatory disorder PAPA syndrome (pyogenic arthritis, pyoderma gangrenosum and acne). Mutation analysis, utilizing direct sequencing, revealed a single base pair change c.293T --> C in the pstpip2 gene resulting in a highly conserved leucine at amino acid 98 being replaced by a proline (L98P). No other mutations were found in the coding sequence of the remaining genes in the refined interval, although a 50 kb gap remains unexplored. These data suggest that mutations in pstpip2 may be the genetic explanation for the autoinflammatory phenotype seen in the cmo mouse.

Fig. 1

Phenotypic and histologic findings in the cmo mouse. (A) 4-month-old BALB/cAnPt-cmo female mouse from our colony with multiple tail kinks. (B) Severe hind foot deformities in a 5-month-old [(B6 × cmo)F1 × cmo] backcross animal that is homozygous cmo for the critical interval on chromosome 18. (C) 9-month-old cmo mouse with firm, erythematous left ear and a normal right ear. (D) Histologic sections of tail stained with H&E from a cmo (right) mouse revealing extensive osteomyelitis evident with areas of dead bone surrounded by an inflammatory infiltrate with a predominance of neutrophils. (E) Lymph node from a cmo mouse with subtle abnormalities including a population of large transformed cells with features of immunoblasts (arrow). (F) H&E stained section of a cmo spleen showing the red pulp with extensive extramedullary hematopoiesis. Although all 3 cell lineages are seen, this area demonstrates an abundance of megakaryocytes (arrows). (G) H&E stained sections from an erythematous, firm ear of a cmo mouse revealing a mixed infiltrate with a predominance of polymorphonuclear cells involving the dermis and epidermis (arrow). (H) H&E stained section demonstrating an inflammatory infiltrate destroying cartilage from the ear of a cmo mouse. (I) Higher power view of H reveals a neutrophilic microabscess invading the cartilage of the ear.

Fig. 2

Informative recombinant mice refine the interval to 1.3 Mb. Microsatellite marker name, cM location and base pair location are shown on the left. Next, the genotyping for the 6 most informative mice are displayed. The mouse number is above each column of genotypes. Mouse numbers preceded by an A represent affected (A) mice (1968, 2049, 2367, 2483), those preceded by a U are unaffected (U) mice (2409, 2456). The genotypes with a crosshatch = cmo homozygotes. Gray solid = B6/cmo F1. DNW = did not work. The candidate genes in the critical region are shown in the box to the far right (http://www.genome.ucsc.edu).

Fig. 3

Mutation in exon 5 of pstpip2 in cmo mice changes a highly conserved leucine to a proline at amino acid 98. The sequence of exon 5 of pstpip2 in a BALB/cByJ control, (cmo × B6)F1 and a cmo mouse showing the c.293T → C (L98P) mutation is shown in the left hand box. The box on the right shows conservation of the leucine 98 in pstpip2 across species.

Fig. 4

Pstpip1 and Pstpip2 share domain homology. Illustrations of murine Pstpip2 (top), human Pstpip2 (middle) and human Pstpip1(bottom) are shown. Domain locations are shown as an approximation and are not drawn exactly to scale. All contain an FCH domain and coil–coil (cc) domains but only Pstpip1 has an SH3 domain. The location of the cmo mutation is shown as a * located at the border of the FCH and coil–coil domains. The * shown in Human Pstpip1 demonstrates the location of the 2 mutations known to cause PAPA syndrome. Protein interactions are below each illustration. PTP PEST = PEST-type tyrosine phosphatase.