Carnitine transporter defect (CTD)

Alternative names	Systemic or primary carnitine deficiency Carnitine uptake defect Deficiency of plasma-membrane carnitine transporter
About the condition	CTD is a fatty acid oxidation disorder. It is a hereditary disease that is caused by a missing protein needed to reabsorb carnitine in the kidney. The features of the condition are caused by intracellular carnitine deficiency, which is needed to convert fat into energy.
Inheritance	Autosomal recessive
Year screening started in WA	2005
Incidence in WA	Approximately 1 in 40,000 births
Defect	Caused by defects in the SLC22A5 gene, which encodes the carnitine transporter OCTN2.
Symptoms if untreated	Hypoketotic hypoglycaemia Vomiting, lethargy, seizures and coma Hepatomegaly Cardiomyopathy Skeletal myopathy
Metabolites on bloodspot screening	Decreased free carnitine (C0) Decreased long-chain acylcarnitines (C16 and C18)
Diagnostic tests	Plasma carnitine Plasma acylcarnitine profile Urine carnitine fractional excretion SLC22A5 gene analysis
Treatment	Carnitine supplementation Avoidance of fasting
Screening issues	Some children with CTD may be asymptomatic Maternal CTD deficiency may be detected incidentally