Citrin deficiency can manifest in newborns as neonatal intrahepatic cholestasis caused by citrin deficiency (NICCD), in older children as failure to thrive and dyslipidemia caused by citrin deficiency (FTTDCD), and in adults as recurrent hyperammonemia with neuropsychiatric symptoms in citrullinemia type II (CTLN2). Often citrin deficiency is characterized by fondness for protein-rich and/or lipid-rich foods and aversion to carbohydrate-rich foods. NICCD: Children younger than age one year have growth retardation with transient intrahepatic cholestasis, hepatomegaly, diffuse fatty liver and parenchymal cellular infiltration associated with hepatic fibrosis, variable liver dysfunction, hypoproteinemia, decreased coagulation factors, hemolytic anemia, and/or hypoglycemia. Although NICCD is generally not severe and symptoms often resolve by age one year with appropriate treatment, some infants succumb to infection and liver cirrhosis and others require liver transplantation. FTTDCD: Around age one to two years, many children with citrin deficiency develop the food preferences mentioned. Some have growth retardation, hypoglycemia, and fatigue as well as hyperlipidemia, pancreatitis, fatty liver, and hepatoma. One or more decades later, some individuals with NICCD or FTTDCD develop CTLN2. CTLN2: Onset is sudden and usually between ages 11 and 79 years. Manifestations are recurrent hyperammonemia with neuropsychiatric symptoms including nocturnal delirium, aggression, irritability, hyperactivity, delusions, disorientation, restlessness, drowsiness, loss of memory, flapping tremor, convulsive seizures, and coma; death can result from brain edema. Symptoms are often provoked by alcohol and sugar intake, medication, and/or surgery. Affected individuals may or may not have a prior history of NICCD or FTTDCD.
The diagnosis of citrin deficiency is suspected from clinical and biochemical findings (in general, increased blood or plasma concentration of ammonia, plasma or serum concentration of citrulline and arginine, plasma or serum threonine-to-serine ratio, and serum concentration of pancreatic secretory trypsin inhibitor [PSTI]). Identification of biallelic mutations in SLC25A13, the only gene in which mutations are known to cause citrin deficiency, confirms the diagnosis.
Citrin deficiency is inherited in an autosomal recessive manner. When both parents are carriers, each sib of an affected individual has, at conception, a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. When one parent is a carrier and the other parent has two mutated SLC25A13 alleles, each sib of an affected individual has, at conception, a 50% chance of being affected and a 50% chance of being an asymptomatic carrier. Carrier testing for at-risk relatives and prenatal testing for pregnancies at increased risk are possible if the disease-causing mutations in the family are known.