The basic helix-loop-helix (bHLH) superfamily of transcription factors have been implicated in a wide range of cellular functions such as proliferation, differentiation, tumorigenesis, and circadian rhythms. In a previous siRNA-based screen, bHLH family member e41 (BHLHE41) had been identified as a putative regulator of neuronal differentiation; however, its function remains largely elusive. To this end, using the CRISPR-Cas9 system, we established an isogenic Neuro2a (N2a) cell line with biallelic targeting of Bhlhe41 gene (Bhlhe41). In undifferentiated N2a cells, complete knockout of Bhlhe41 resulted in marked proliferation inhibition, together with accumulation of apoptotic cells. Furthermore, retinoic acid (RA)-induced neurite outgrowth and expression of neuronal markers are significantly weakened in Bhlhe41 cells. We also showed that the activity of ERK1/2 signaling, a key regulator of neuronal differentiation, is likewise impaired in knockout cells. Together, these results suggest that Bhlhe41 plays critical roles in regulating cell death and neurite outgrowth in N2a cells.

Rationale: Polyglandular autoimmune syndromes (PAS) are a heterogeneous group of rare diseases characterized by the association of at least 2 organ-specific autoimmune disorders, concerning both the endocrine and nonendocrine organs. Type III is defined as the combination of autoimmune thyroid disease and other autoimmune conditions (other than Addison disease), and is divided into 4 subtypes. We describe a patient with Hashimoto thyroiditis, adult-onset Still disease, alopecia, vasculitis, antineutrophil cytoplasmic antibody (ANCA)-mediated crescentic glomerulonephritis, and hyperparathyroidism. Co-occurrence of these 5 diseases allowed us to diagnose PAS type IIIc. The rare combination of these different diseases has not been reported before. Patient concerns: A 51-year-old woman was admitted in April, 2019 after the complaint of an enlarged thyroid. She was diagnosed with Hashimoto thyroiditis at the age of 36. At age 40, she was diagnosed with an adult-onset Still disease. Three months before admission, she experienced renal insufficiency. After admission, she was diagnosed with hyperparathyroidism. Diagnosis: Renal biopsy revealed renal vasculitis and crescentic nephritis. Antineutrophil cytoplasmic autoantibody showed that human perinuclear ANCA and myeloperoxidase ANCA were positive. Therefore, the patient was diagnosed with vasculitis and ANCA-mediated crescentic glomerulonephritis. After admission, parathyroid single-photon emission computed tomography/computed tomography fusion image demonstrated the presence of hyperparathyroidism. Interventions: The patient was treated with high-dose methylprednisolone pulse therapy (0.1 g/d) for vasculitis and ANCA-mediated crescentic glomerulonephritis, calcium and vitamin D3 (600 mg/d elemental calcium [calcium carbonate] and 2.5 μg/d active vitamin D3) for hyperparathyroidism, and levothyroxine sodium (50 ug/d) for Hashimoto thyroiditis. Outcomes: Up to now, serum thyroid-stimulating hormone, total triiodothyronine, total thyroxine, free triiodothyronine, and free thyroxine were within the normal ranges. Patient's renal function did not deteriorate. Lessons: We report a patient with Hashimoto thyroiditis, adult-onset Still disease, alopecia, vasculitis, ANCA-mediated crescentic glomerulonephritis, and hyperparathyroidism, which is a very rare combination. We present this case as evidence for the coexistence of several different immune-mediated diseases in the clinical context of a PAS IIIc.