RT Book, Section
A1 Morris, Andrew A.M.
A1 Chakrapani, Anupam
A2 Sarafoglou, Kyriakie
A2 Hoffmann, Georg F.
A2 Roth, Karl S.
SR Print(0)
ID 1140316683
T1 Tyrosinemias and Other Disorders of Tyrosine Degradation
T2 Pediatric Endocrinology and Inborn Errors of Metabolism, 2e
YR 2017
FD 2017
PB McGraw-Hill Education
PP New York, NY
SN 9780071773140
LK accesspediatrics.mhmedical.com/content.aspx?aid=1140316683
RD 2024/04/19
AB Tyrosine  is  derived  from  the  diet,  from  metabolism  of  phenylalanine,  and  from  the  body’s  proteins  during  catabolic  stress.  Tyrosine  degradation  is  catalyzed  by  a  series  of  five  enzymatic  reactions,  with  end  products  being  acetoacetate  and  fumarate.  The  hepatocyte  and  renal  proximal  tubules  are  the  only  two  cell  types  that  express  the  complete  pathway  and  contain  sufficient  quantities  of  all  enzymes  required  for  tyrosine  catabolism  (Figure  17–1).  Normal  plasma  tyrosine  concentrations  are  between  30  and  120  μmol/L.  Increased  concentrations  of  tyrosine  in  plasma  are  common  and  may  be  the  result  of  a  primary  inherited  metabolic  disorder,  but  they  may  also  be  secondary.  The  most  common  causes  are  listed  in  Table  17–1.  The  primary  disorders  are  all  defects  in  the  tyrosine  degradation  pathway.  The  first  is  tyrosine  aminotransferase  deficiency  (tyrosinemia  type  2)  and  the  second  is  4–hydroxy-phenylpyruvate  dioxygenase  deficiency  (tyrosinemia  type  3).  The  most  common  disorder  in  the  pathway,  however,  is  a  defect  of  the  last  enzyme,  namely  fumarylacetoacetase,  which  causes  tyrosinemia  type  1  (also  known  as  hepatorenal  tyrosinosis).  The  most  common  secondary  causes  of  high  plasma  tyrosine  concentrations  are  acute  liver  disease  and  transient  neonatal  tyrosinemia.