The amount of a S-adenosylmethionine synthetase isoform type-1 when measured in blood serum. The trait is level of S-adenosylmethionine synthetase isoform type-1 in blood serum (Ontology of Biological Attributes entry OBA_2042304). Also known as: blood serum S-adenosylmethionine synthetase isoform type-1 amount.