Citrin deficiency (CD) is an autosomal recessive disorder caused by the absence or dysfunction of the mitochondrial transporter citrin, resulting from mutations in SLC25A13. The disease presents with age-dependent clinical manifestations: neonatal intrahepatic cholestasis caused by CD (NICCD), failure to thrive and dyslipidemia by CD (FTTDCD), and an adult-onset form (formerly called Type II citrullinemia, CTLN2, recently renamed to “adolescent and adult citrin deficiency,” AACD). The gene discussed is SLC25A13; the disease is neonatal intrahepatic cholestasis due to citrin deficiency.