• Inflammatory protein biomarkers aid complex diagnosis of rare genetic disease

    A five-year old child infected by SARS-CoV-2 developed severe symptoms of arthralgia (joint pain) and thromobocytopenia (abnormally low platelet count), revealing significant dysregulation of their immune system. This condition, called Haploinsufficiency of Suppressor of Cytokine Signaling (SOCS1) is accompanied by excessive B-cell activity, an increase of a type of white blood cell called eosinophils, and high levels of IgE antibodies. The Olink® Target 48 Cytokine panel was used to confirm up-regulation of multiple interferon (IFN)-inducible genes, comparable to dysregulation observed in systemic lupus erythematosus (SLE).

    An autoimmune diagnostic odyssey

    Imagine the diagnostic odyssey of parents with a sick child: severe joint pain and inflammation of the tendons (called enthesitis), occurring three months after a mild case of SARS-CoV-2 infection. This 5-year-old child had difficulty walking, severe pain with limited motion of the legs and hips, and swelling of the wrists and finger joints.

    Muscle strength was normal, and a battery of clinical tests showed moderate increase in eosinophils but otherwise normal blood cell counts. After ruling out many potential diagnoses, the attending physicians at both University of Michigan and Boston Children’s Hospital settled on ‘juvenile idiopathic arthritis’ with an unknown cause.1

    Standard therapy for arthritis (a drug called naproxen) did not help, and a drop in the platelet count (called mild thrombocytopenia) initiated another round of diagnostic assessments. Testing for parasites was negative, along with metabolic disorders. Genetic testing for eosinophil disorders and a skin biopsy to test for esosinophilic fasciitis were also negative. Worsening buildup of synovial fluid in the tendons (called tenosynovitis) was detected through MRI, which led the treating physicians to perform a bone marrow biopsy to look for cancer.

    The genetic karyotyping and flow cytometry analysis of bone marrow for malignancy also came up negative. The bone marrow biopsy did reveal low cellularity, however, at 50%.

    After hospital admission, additional symptoms developed, including wet purpura (blood blisters), epistaxis (nosebleeds),hematuria (blood in the urine), melena (black, tar-colored stools). Remarkably at one point the platelet count reached 0 K/µL. An oral corticosteroid, prednisone, was administered along with immunoglobulins but the patient did not improve.

    Additional tests of bone marrow revealed no signs of malignancy, and the physicians reasoned there was some underlying rheumatologic disorder and treated the patient with a combination of rituximab and romiplastin. Rituximab is a treatment for rheumatoid arthritis, targeting the CD20 protein found on B lymphocytes, while romiplostim is a standard treatment for chronic immune thrombocytopenia, an autoimmune disorder where platelets are destroyed by the immune system.

    Dysfunctioning SOCS1 haploinsufficiency: a rare disease unmasked by COVID infection

    The patient’s platelet count recovered in a matter of days and they were discharged from hospital. In the ensuing weeks, additional genetic testing revealed a deletion of one 5-megabase section of chromosome 16, that included the seven genes in the table below.

    Gene Dominant or Recessive Condition
    SOCS1 Dominant Autoinflammatory syndrome, familial
    GRIN2A Dominant Epilepsy, with speech disorder
    EMP2 Recessive Nephrotic syndrome, Type 10
    CIITA Recessive Bare lymphocyte syndrome, Type II
    LITAF Dominant Charcot-Marie-Tooth disease, Type 1C
    ERCC4 Recessive Fanconi anemia, complementation group Q
    PARN Dominant Pulmonary fibrosis and/or bone marrow failure

    Careful analysis by the treating physicians ruled out all of the listed genes except SOCS1, leading them to suspect this was a case of SOCS1 haploinsufficiency, where a mutation (or a single-copy deletion) leads to incomplete penetrance of a trait (in this case a dominant disorder).

    SOCS1 is a known negative regulator of type I and type II interferon (IFN) signaling by inhibiting activation of Janus kinase (JAK). Through SOCS1 haploinsufficiency, IFN signaling is abnormally high.

    A multiomic analyses leads to an IFN Signature

    To demonstrate IFN signaling, RNA sequencing of peripheral blood mononuclear cells (PBMCs) demonstrated that IFN-inducible genes were upregulated in the proband compared to unaffected family members. These findings were confirmed through surface marker analysis by flow cytometry, as well as upregulation of circulating cytokines by the Olink Target 48 Cytokine Panel.2 The 10 significantly up-regulated cytokines regulated by the JAK pathway are IL-1beta, IL-6, IL-7, IL-10, IL-18, IL-27, IFN-gamma, TNF, GM-CSF, and VEGF-A.

    A critical JAK-STAT pathway leads to successful treatment

    With a likely diagnosis in-hand, the patient was started on a JAK inhibitor called tofacitinib, an FDA-approved JAK1/JAK3 inhibitor for treatment of juvenile idiopathic arthritis. Within a month, the patient’s joint pain and inflammation improved and platelet counts remained normal, even though the patient’s B-cell population recovered after cessation of treatment with rituximab.

    At the time of publication, the patient had taken the JAK inhibitor for 10 months without disease flare or adverse side effects.

    In their discussion the authors note “our case highlights a need to utilize a multidisciplinary approach and consider comprehensive genetic evaluations in those with atypical ITP (idiopathic thrombocytopenia). Inborn errors of immunity are increasingly recognized to manifest with varying clinical and laboratory manifestations. Collectively, the prevalence of these monogenic conditions may be as high as 1 in every 1200 to 2000 individuals.”3

     

    References

    1. Michniacki TF, Lee PY et al. SOCS1 Haploinsufficiency Presenting as Severe Enthesitis, Bone Marrow Hypocellularity, and Refractory Thrombocytopenia in a Pediatric Patient with Subsequent Response to JAK Inhibition. J Clin Immunol. 2022 1-12. https://link.springer.com/article/10.1007/s10875-022-01346-x
    2. https://www.olink.com/products-services/target/48-cytokine-panel/
    3. Chinn IK, Orange JS. Immunodeficiency Disorders. Pediatr Rev. 2019 40(5):229-242. doi:1542/pir.2017-0308

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