Reacción a "Reactions to the analysis linking certain gastrointestinal diagnoses with Parkinson's disease"

It has long been understood that the brain communicates with the gut and some have hypothesized that factors emanating from the gut could trigger the development of neurological conditions, such as Parkinson’s disease (PD).  The paper in Gut makes an important contribution by showing that some gastrointestinal diagnoses are linked to a later diagnosis of PD, suggesting that it may be important for doctors to take note of these GI conditions when evaluating patients at risk for PD, even prior to the onset of neurological symptoms.  The authors’ conclusions are well-supported by the large number of patient health records that were compared in the study, and by the fact that they analyzed the association between GI conditions and PD in both directions and obtained the same results (i.e., do those with PD have a history of these GI conditions and do those with specific GI conditions go on to develop PD in the ensuing five years).

Moreover, the investigators were careful to minimize the impact of surveillance bias in their analysis (i.e., the more you look, the more you find).  However, the subjects whose records were reviewed were less racially and ethnically diverse than the US population overall, meaning that it might not be possible to extrapolate the conclusions to all groups or indeed those outside the US.  Also, the findings are purely correlative, and it remains possible that both GI conditions and PD are independently linked to an as yet unknown third risk factor – the work reported cannot ascribe causality.  Nevertheless, the conclusions may have clinical relevance and certainly should prompt additional studies to identify underlying mechanisms because there are potential implications for early treatment.