RT Book, Section
A1 Gou, Eric W.
A1 Anderson, Karl E.
A2 Kang, Sewon
A2 Amagai, Masayuki
A2 Bruckner, Anna L.
A2 Enk, Alexander H.
A2 Margolis, David J.
A2 McMichael, Amy J.
A2 Orringer, Jeffrey S.
SR Print(0)
ID 1161338406
T1 The Porphyrias
T2 Fitzpatrick's Dermatology, 9e
YR 2019
FD 2019
PB McGraw-Hill Education
PP New York, NY
SN 9780071837798
LK accessmedicine.mhmedical.com/content.aspx?aid=1161338406
RD 2024/04/25
AB Porphyrias  are  metabolic  diseases  caused  by  abnormalities  of  the  8  enzymes  in  the  heme  biosynthetic  pathway.  All  but  one  arise  from  mutation  of  a  pathway  enzyme;  the  exception  is  porphyria  cutanea  tarda  (PCT),  which  develops  as  an  acquired  deficiency  of  the  fifth  enzyme  in  the  pathway  with  or  without  a  mutation.  Porphyrias  are  classified  as  hepatic  or  erythropoietic  based  on  whether  heme  precursors  first  accumulate  in  liver  or  bone  marrow,  the  tissues  that  most  actively  synthesize  heme.  Porphyrias  are  categorized  clinically  based  on  their  clinical  features  as  either  cutaneous  or  acute  (Table  124-1).  Cutaneous  porphyrias  are  due  to  overproduction  and  accumulation  of  photosensitizing  porphyrins.  Most,  as  exemplified  by  PCT,  cause  chronic  blistering  and  scarring  on  sun-exposed  areas  of  skin,  whereas  protoporphyrias  produce  an  acute,  severe,  and  mostly  nonblistering  reaction  to  light,  often  leaving  few  if  any  chronic  skin  changes.  Acute  porphyrias  are  characterized  by  neurologic  symptoms  and  elevated  levels  of  the  porphyrin  precursors,  δ-aminolevulinic  acid  (ALA)  and  porphobilinogen  (PBG).  Porphyrins  also  accumulate  in  acute  porphyrias,  and  sometimes  achieve  levels  in  plasma  sufficient  to  cause  cutaneous  blistering,  as  exemplified  especially  by  variegate  porphyria  (VP).  In  some  porphyrias,  damage  to  other  organs,  such  as  liver  and  kidney,  may  also  occur.  Symptoms,  signs,  and  histologic  findings  caused  by  porphyrias  are  nonspecific,  whereas  patterns  of  porphyrins  and  porphyrin  precursors  enable  specific  diagnoses  and  treatments  (Table  124-2).