Additionally, DNA‐analysis is sometimes warranted to differentiate between porphyrias with similar clinical presentation if biochemical findings are not definitive (e.g. FECH deficient and X‐linked EPP), to facilitate family investigations, especially for acute porphyrias where asymptomatic family members at risk are advised to have predictive genetic testing, and to inform on prognosis in CEP. This evidence concerns the gene FECH and cutaneous porphyria.