Review for 10.1186/1471-230X-5-11 (2005)

Reviewer's report 
 The relation between plasma tyrosine concentration and fatigue in primary biliary cirrhosis and Title: 
primary sclerosing cholangitis 
 1  14 October 2004 Version: Date: 
 U Leuschner Reviewer: 
Reviewer's report: 
General 
Review of the manuscript The relation between plasma tyrosine concentration and fatigue in primary 
biliary cirrhosis and primary sclerosing cholangitis. Authors: PCJ ter Borg et al. 
The authors investigated the relation between amino acid concentrations in the plasma and fatigue 
in patients with PBC and PSC, and chronic hepatitis C and compared their results with those of healthy controls. They found marked abnormalities in the plasma amino acid pattern compared to 
controls and that low tyrosine concentrations are associated with fatigue and reduced quality of live. 
The latter were established using the Fisk fatigue severity scale, a visual analogue scale and to quantify the results the SF-36 score. 
This is an interesting manuscript because fatigue, wich occurs in 80 to 90% of patients with PBC or 
PSC is a major clinical problem. The etiology of fatigue in PBC is not understood. Since the neurotransmitters serotonin and norepinephrine seem to play an important role in the development 
of fatigue by stimulating the corticotropin-releasing hormone (CRH) in the hypothalamus, the authors 
calculated the tryptophan and the tyrosine ratios, but were unable to find any results that could help 
to increase our understanding of fatigue etiology.. 
Other factors discussed as pathogenic mechanisms of fatigue are an activation of the HPA axis 
(hypothalamic-pituitary-adrenal axis) and the expression of cytokines like IL-1, IL-6, IL-1 Beta and 
TNF-Alpha during inflammation. Most likely fatigue is a problem of central CRH-release or of the HPA axis since CRH has central effects and induces behavioural changes. Physical and psychological stress are also stimuli for an increased CRH release. 
These aspects should be discussed and emphasized by the authors in the discussion. 
Nevertheless, it is commendable that the authors investigated amino acid patterns in patients with cholestatic liver diseases and fatigue, since amino acids have been investigated in many studies 
with patients with hepatic encephalopathy and since the etiology of fatigue still lies in darkness and 
all aspects that might be responsible are worthwhile to be discussed. 
In detail the following aspect need to be discussed or improved : 
1. Abstract: did patients without fatigue and good quality of live also have an increase of tyrosine? 
2. Methods: the numbers for PBC-, PSC- and chronic hepatitis C-patients must be included in the 
text of this chapter. 
3. Methods: it is not clear whether chronic hepatitis C-patients and the 73 healthy individuals served 
as controls for amino acid measurement only and the additional 18 age- and sex-matched controls 
for the questionnaires, or whether the questionnaires were also obtained from the hepatitis 
C-patients and the 73 healthy subjects. It is important to get questionnaires also from the healthy 
subjects and from hepatitis C patients in order to characterise the mental situation of the normal 
population and to exclude that in PBC- and PSC-patients any association between amino acids and 
the mental situation was poorly by chance. The HCV patients show prominent amino acid pattern changes same as in PBC. 
4. Table 1: Please give normal values and range as foot notes and add prothrombin time which 
together with bilirubin and albumin is an accepted prognostic factor. How many PSC-patients had an 
association with IBD and could IBD influence amino acid concentrations in the plasma? 
5. Results: in the abstract you stated that the branched chain amino acids valine, leucine and 
isoleucine are increased, but in table 2 they are significantly decreased. Significance is not <.002. All
tables need a title. In the first line of table 2 the numbers of controls has to be added. 
6. In my version there is no table 4. If you have one, please add it to the manuscript. 
7. Table 3: Instead of Fisk the term FFSS should be preferred because FFSS has already been used 
in the chapter “methods”. 
8. The text on page 3 /4 from “Testing for differences in….” until “……. domains of the SF 36 (fig. 1 
and 2)” is difficult to read. 
9. Figure 1 and 2: In the legend the word “normal” has to be added: normal/low tyrosine. 
10. Discussion: 
Line 7: The word “further” can be deleted. 
Line 15: When you write that in several studies on hepatic encephalopathy amino acids have been 
studied then please give more than one (7) reference. 
A new paragraph should be started with “Tyrosine and phenylalanine are mainly …..” 
Line 3: In this line of the new para. the term “in this study” should be replaced by “in our study”. 
Line 4 of the new para: Please give references for immune activation by tryptophan and that immune 
activation may reduce tryptophan concentrations in the plasma. 
Line 6, 9: Give references. 
In the para beginning with “Fatigue is a …..” the term “these diseases” should be replaced by “with 
PBC and PSC” or “chronic liver diseases”. 
In the para beginning with “An effective medical treatment ….” The word “numerous” is strongly 
exaggerating. Please give references or better delete this para completely. 
 Unable to decide on acceptance or rejection until the authors have responded to the What next?: 
major compulsory revisions