All the other patients with AD/CMRD, for which the gene defect has been established, exhibit mutations in the SAR1B gene (located on chromosome 5) which are believed to incapacitate the SAR1B protein in its role in COPII-dependent transport and result in the defect of secretion of chylomicrons in the intestine. The gene discussed is SAR1B; the disease is chylomicron retention disease.