CBLN1 and obesity due to melanocortin 4 receptor deficiency: They constructed ceramide synthase 5 or Cers6 knockout mice and found that only knockout of Cers6 could regulate CER (d18:1/16:0) in mitochondria and mitochondria-associated membrane structures, and ultimately improved obesity-related insulin resistance, while ceramide synthase 5 deficiency showed no improvement (32).