Hi David, 

What you need is the Ensembl Variant Effect Predictor. (I attached the text file with the output)

In assembly GRCh38, your relevant gene (CBS) is on chromosome 21, positions 43,053,191 to 43,076,943; reverse strand; so your SNP is at position 43053889. 

I.e. a change from a C to a T on the reverse strand is a change from a G to an A on the forward strand so the codon change is gaG/gaA and this is a synonymous variant! Your amino acid will stay being a Glutamic acid (E) regardless of the mutation. 

However synonymous variants have been implicated in diseases a few times, if you have found another example that is really interesting (see links to papers)!

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0048541

https://www.nature.com/nrg/journal/v8/n2/full/nrg2056.html

https://www.nature.com/nrg/journal/v7/n2/full/nrg1770.html

http://science.sciencemag.org/content/315/5811/525

Hi Jan, Thanks for the response - that was my conclusion too, but had t check. Cannot see the link you mention.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0048541

http://science.sciencemag.org/content/315/5811/525

https://www.nature.com/nrg/journal/v7/n2/full/nrg1770.html

https://www.nature.com/nrg/journal/v8/n2/full/nrg2056.html

Thanks