Mice with Bmp6 deficiency[12], Hjv deficiency [13]–[14], or hepatocyte-specific Hjv[15] or Smad4[16] deletion all have severely reduced Hamp1 expression and a phenotype that closely resembles Hamp1-deficient mice [1]; therefore, the Bmp6/Hjv/p-Smad1/5/8 pathway clearly plays a key role in Hamp1 regulation [17]. Here, HJV is linked to hyperinsulinemic hypoglycemia, familial, 4.