You are examining a 2-year-old girl brought in by her parents because they are concerned about her lack of any type of talking and she seems unusually clumsy. History reveals that the child has had numerous upper respiratory infections over the past 6 months. You suspect the child is suffering from a particular form of a lysosomal storage disease. Genetic testing reveals a missense mutation in the N-aspartyl-β-glucosaminidase gene. This child is most likely suffering from which of the following defects in glycoprotein metabolism?

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Aspartylglucosaminuria is a lysosomal storage disease caused by a deficiency in the enzyme N-aspartyl-β-glucosaminidase, leading to the accumulation of glycoasparagines. The symptoms and genetic mutation described match this condition. Aspartylglucosaminuria belongs to a family of disorders identified as lysosomal storage diseases. This disorder is characterized by the lysosomal accumulation of glycoasparagines, primarily aspartylglycosamine. These glycoasparagines accumulate in the lysosomes as a consequence of defects in the lysosomal hydrolase, N-aspartyl-β-glucosaminidase. The hallmark symptom of aspartylglucosaminuria is a global delay in psychomotor development that begins between 2 and 4 years of age. There is a period of frequent upper respiratory infections followed by delayed speech and physical clumsiness. The disorder in speech development is a cardinal sign of mental retardation and is usually the first indication to parents that there is something amiss with their child.

You Are Examining a 2-Year-Old Girl Brought in by Her