With autism in mind, there is a body of evidence on BDNF which suggests a few things albeit not exactly consistently:
- I am a little bit unsure whether BDNF is meant to be 'generally' high or low in cases of autism. Accepting the factors which can influence BDNF listed above, there seems to be some conflicting evidence on findings related to blood/plasma. So for example, this paper by Al-Ayadhi** (full-text), an author mentioned in previous posts, reported lower levels of serum BDNF in their cohort of children with autism. This contrasts with this paper by Connolly and colleagues*** who reported elevations in BDNF. Just to complicate matters further Lisa Croen and colleagues**** (full-text) reported no significant differences in blood concentrations of BDNF in either mums mid-pregnancy nor their young offspring subsequently diagnosed with autism compared with asymptomatic and learning disability control participants. I might be comparing apples and oranges at different times of year, but suffice to say that results are not yet clean-cut.
- When it comes to genes and BDNF in cases of autism, the waters aren't really any less muddy. This paper by Correia and colleagues***** reported elevations in plasma BDNF in their autism cohort but the source of the increase did not seem to stem from issues with the BDNF gene. Without being an expert on all things genetic, I think this finding might also tie into the results published by Garcia and colleagues****** who suggested that BDNF elevations might not be "transcriptionally driven" (see here for a summary of mRNA). There are other studies looking at other features of BDNF seemingly reporting contrasting findings such as decreased BDNF and anti-apoptotic function (here) and SNPs in the BDNF gene in autism (here andhere). The message continues: it's complicated.
Thank you, Paul!