Noonan syndrome (NS) is a dominantly inherited genetic disorder with mutations in genes encoding components or regulators of the RAS/mitogen-activated protein kinase pathway. Its diagnosis is based on characteristic features, including typical facial features, a short stature, congenital heart disease, mild developmental delay, and cryptorchidism. Patients with NS sometimes develop autoimmune diseases, such as Hashimoto's thyroiditis and, rarely, systemic lupus erythematosus (SLE). We herein present a 29-year-old Japanese female with NS complicated by SLE and repeated severe hypoglycemia. The patient was diagnosed with SLE based on thrombocytopenia, nephritis, a positive antinuclear antibody titer (1:640), and a positive anti-dsDNA antibody. The patient was treated with a glucocorticoid, mycophenolate mofetil, and tacrolimus, which attenuated both SLE and hypoglycemia. Since insulin receptor antibody levels were higher to the upper normal range and decreased after treatment, hypoglycemia probably appeared to be attributed to type B insulin resistance syndrome (TBIRS). We herein present the first case of SLE in NS complicated by TBIRS. Although NS is a rare disease, we need to consider the complication of autoimmune diseases, including SLE.
Keywords: Noonan syndrome; RASopathy; hypoglycemia; systemic lupus erythematosus; type B insulin resistance syndrome.
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