Mais attendu

16:49 May 24, 2017 

It was addressed to you :-)
The point I was making was that "whereas" would be confusing here, since it implies a contrast or opposition, which is not the case.
In your example, "whereas I like jam", whereas means "although". In the text you're translating, "attendu que" means "since", which is the opposite of "although".
Have one for me - it's still slightly too early for G&Ts here!

16:45 May 24, 2017 

I'm not sure to whom your comment is addressed, me or Nikki. I may be confused, or I may be very lucid. It often depends how many G&Ts I happen to have had. Suffice to say that M'Learned friends use "Whereas" where "Nos amis doctes" use "attendu que". I agree that in legalese it is synonymous with "since".

15:51 May 24, 2017 

I think you may be confusing the two meanings of 'whereas'. In normal English it means 'by contrast'. In legalese it means the exact opposite, 'since'. In fact the latter might be a better translation.

08:35 May 24, 2017 

http://blog.oxforddictionaries.com/2012/01/can-i-start-a-sen...

See about half way down the page.

08:30 May 24, 2017 

"Whereas" works for "attendu que" in ordinary EN too.
There are circumstances where you can start a sentence with "but". Making sense of your extract will depend on what has gone before. Perhaps you could post the sentence that precedes. It would probably help to post the end of the sentence too. In any event, the meaning no doubt remains the same.

You basically have a string of subordinate clauses and indeed the extract you have posted has no main clause, without which the full context of the sentence cannot be understood.