The Serum Alpha-N-Acetylglucosamines measures the levels N-acetylglucosaminidase (NAG) activity. Deficiency in NAG leads to the progressive intralysosomal accumulation of the glycosaminoglycan heparan sulfate. Symptoms of such deficiency are characterized by behavioral changes and mental deterioration, resulting in severe dementia and early mortality. This test is used to detect Mucopolysaccharidosis type IIIB, also known as Sanfilippo syndrome B.