Type Ia Glycogen Storage Disease Workup

Updated: Mar 07, 2017
  • Author: Wayne E Anderson, DO, FAHS, FAAN; Chief Editor: George T Griffing, MD  more...
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Workup

Laboratory Studies

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  • Obtain a creatine kinase level in all cases of suspected glycogen storage disease (GSD).

  • Because hypoglycemia may be found in some types of GSD, fasting glucose testing is indicated. Hypoglycemia is concerning and may lead to hypoglycemic seizures.

  • Urine studies are indicated because myoglobinuria may occur in some GSDs.

  • Hepatic failure occurs in some GSDs. Liver function studies are indicated.

  • Hyperlipidemia is found in GSD Ia although there is no clear evidence of increased atherosclerosis. [7]

  • Laboratory abnormalities also include hyperuricemia, hyperlactacidemia, hyperlipidemia, hypercalciuria, and azotemia.

  • Normochromic anemia has been documented.

  • Measuring lipase and amylase may be justified in suspected cases of pancreatitis.

  • Renal function studies may reveal renal failure. Nephropathy is a serious long-term complication of von Gierke disease.

  • Obtaining a 24-hour urine collection to measure protein and creatinine clearance may be useful.

  • Nutritional status

    • Kishnani and colleagues reported on 1 patient with von Gierke disease who was compliant with a high-protein diet but who developed emesis, weight loss, weakness, ataxia, agraphia, and oral ulcers. He was found to be deficient in vitamin B-12, folate, and iron. Correction of deficiencies allowed for symptomatic recovery. [8]

    • Other authors note that oral ulcers are secondary to impaired neutrophil migration, one feature of this disorder.

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Imaging Studies

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  • Imaging may reveal hepatic adenoma, which may become malignant.

  • Bone densitometry in older individuals may show low bone mass.

  • Renal ultrasonography may show enlarged kidneys.

  • In a study to determine how well contrast-enhanced ultrasonographic scans can characterize focal liver lesions in patients with GSD type Ia, Nguyen et al examined images from 8 benign hepatic adenomas associated with the disease. [9] The scans revealed marked hypervascularity in all of the lesions during the early arterial phase, with most of the lesions showing sustained enhancement in the portal and late phases.

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Other Tests

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  • Ischemic forearm test

    • The ischemic forearm test is an important tool for diagnosis of muscle disorders. The basic premise is an analysis of the normal chemical reactions and products of muscle activity. Obtain consent before the test.

    • Instruct the patient to rest. Position a loosened blood pressure cuff on the arm, and place a venous line for blood samples from the antecubital vein.

    • Obtain blood samples for the following tests: creatine kinase, ammonia, and lactate. Repeat in 5-10 minutes.

    • Obtain a urine sample for myoglobin analysis.

    • Immediately inflate the blood pressure cuff above systolic blood pressure and have the patient repetitively grasp an object, such as a dynamometer. Instruct the patient to grasp the object firmly, once or twice per second. Encourage the patient for 2-3 minutes, at which time the patient may no longer be able to participate. Immediately release and remove the blood pressure cuff.

    • Obtain blood samples for creatine kinase, ammonia, and lactate immediately and at 5, 10, and 20 minutes.

    • Collect a final urine sample for myoglobin analysis.

  • Interpretation of ischemic forearm test results

    • With exercise, carbohydrate metabolic pathways yield lactate from pyruvate. Lack of lactate production during exercise is evidence of a pathway disturbance, and an enzyme deficiency is suggested. In such cases, muscle biopsy with biochemical assay is indicated.

    • Healthy patients demonstrate an increase in lactate of at least 5-10 mg/dL and ammonia of at least 100 mcg/dL. Levels will return to baseline.

    • If neither level increases, the exercise was not strenuous enough and the test is not valid.

    • Increased lactate at rest (before exercise) is evidence of mitochondrial myopathy.

    • Failure of lactate to increase with ammonia is evidence of a GSD resulting in a block in carbohydrate metabolic pathways. Not all patients with GSDs have a positive ischemic test.

    • Failure of ammonia to increase with lactate is evidence of myoadenylate deaminase deficiency.

    • In von Gierke disease, the ischemic forearm test is negative.

  • Molecular genetic analysis

    • Seydewitz and Matern report a study of 40 patients with von Gierke disease. Mutations were found on all 80 alleles, which is evidence that molecular genetic analysis is a reliable diagnostic modality in addition to enzyme assay. [10]

    • Biochemical assay of enzyme activity is required for definitive diagnosis.

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Histologic Findings

Biopsy of the kidney reveals focal glomerulosclerosis.

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