Published online by Cambridge University Press: 01 June 2011
Porphyrias are disorders caused by heritable or acquired deficiency of an enzyme that is required for the normal synthesis of heme. A ring structure, heme is formed by the insertion of an iron atom into protoporphyrin in the final step of the porphyrin synthesis pathway. The usual presenting symptoms and signs of porphyrias are either skin photosensitivity or neurovisceral symptoms and signs. Three types of porphyria are characterized by a predominance of photosensitivity (porphyria cutanea tarda (PCT), congenital erythropoietic porphyria, and erythropoietic protoporphyria). Two types of porphyria are characterized mainly by neurovisceral symptoms and signs (acute intermittent porphyria and aminolevulinate dehydratase deficiency). The two remaining types of porphyria are characterized by both photosensitivity and neurovisceral symptoms and signs (hereditary coproporphyria and variegate porphyria). The seven main types of porphyria, the associated enzyme deficiency, the mode of inheritance, and the major presenting symptoms and signs are displayed in Table 10.1. The only type of porphyria discussed here is PCT, the most common of all porphyrias.
Porphyria cutanea tarda (PCT)
PCT is estimated to occur in about 1 per 5000 to 25,000 individuals in the general population. PCT is caused by decreased specific activity of the uroporphyrinogen decarboxylase enzyme, the fifth enzyme in the heme synthesis pathway. Three types of PCT can be identified on the basis of decreased activity of the uroporphyrinogen decarboxylase enzyme (URO-D) in liver cells or in erythrocytes.
To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Find out more about the Kindle Personal Document Service.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Dropbox.
To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.