I do not quite understand why deficieincy in branching enzyme can cause glucogen storage disease. It seems all other glucogen storage diseases are caused by enzymes that are needed for glucogenolysis. So why branching enzyme?
its because branching enzyme i.e.alpha 1;4:1;6 transferase..is required to break 1;4 bond and move it to 1;6 bond...branches have terminal glucose attached to it which can be released rapidly on demand..
also in linear glycogen there is just one terminal glucose while branched glycogen has 8-10% of R-terminal glucose..
hope this helps.