Mutations in the RNA component of RNase mitochondrial RNA processing might cause Omenn syndrome.
BACKGROUND
Omenn syndrome is a variant of severe combined immunodeficiency disease, which most prominently presents with erythroderma, eosinophilia, and susceptibility to various pathogens. Mutations in the nucleases of recombination activating genes 1 and 2 (RAG1/RAG2) or Artemis were found in some, but not all, patients with Omenn syndrome. We identified 2 patients who presented with clinical features consistent with Omenn syndrome but had no mutations in RAG or Artemis. Both patients also had cartilage-hair hypoplasia (CHH).


OBJECTIVE
We sought to define the molecular basis and characterize the features of severe combined immunodeficiency and Omenn syndrome in these patients.


METHODS
We have studied humoral and cellular immunity using standard assays. T-cell repertoire was investigated by quantitating Vbeta families. The RNase mitochondrial RNA processing (RMRP) RNA gene was sequenced by using standard techniques.


RESULTS
Sequence analysis of the RMRP RNA gene showed that each patient had an insertion-duplication on one allele and a point mutation on the other allele. These point mutations were novel, and they might be related to the unusual presentation of Omenn syndrome in addition to CHH in these patients. Indeed, analysis of the thymus showed residual mature T lymphocytes. This leaky thymus might be responsible for the skewed release of some T-cell clones into the circulation, which might trigger the phenotype of Omenn syndrome.


CONCLUSIONS
We have demonstrated that mutations in the RMRP RNA gene might be associated with Omenn syndrome.


CONCLUSIONS
This discovery will aid clinicians in the early recognition and treatment of CHH-associated Omenn syndrome.
Roifman
Chaim M
CM
Division of Immunology and Allergy and Program of Infection, Immunity, Injury and Repair, The Hospital for Sick Children and The University of Toronto, Ontario, Canada. chaim.roifman@sickkids.ca
Gu
Yiping
Y
Cohen
Amos
A
D001483:Base Sequence; D016026:Bone Marrow Transplantation; D004247:DNA / Q000235:genetics; D004722:Endoribonucleases / Q000235:genetics* / Q000378:metabolism; D005260:Female; D006801:Humans; D007223:Infant; D009154:Mutation; D012313:RNA / Q000235:genetics*; D012323:RNA Processing, Post-Transcriptional; D016511:Severe Combined Immunodeficiency / Q000201:enzymology* / Q000235:genetics* / Q000276:immunology / Q000628:therapy; D013577:Syndrome; D013601:T-Lymphocytes / Q000276:immunology
D012313:RNA; D004247:DNA; D004722:Endoribonucleases; C058330:mitochondrial RNA-processing endoribonuclease