BIOCHEMICAL ASSAYS FOR MUSCLE GLYCOGENOSES AND LIPID DISORDERS
Muscle glycogenoses typically cause one of two major clinical syndromes: (1) exercise intolerance, with exercise-related myalgia and contractures, with or without recurrent episodes of muscle breakdown ("rhabdomyolysis") and myoglobinuria; (2) weakness, with varying severity, age at onset, and distribution pattern. In Figure 1, the glycogenoses associated with the first syndrome are indicated by the bold numerals, and those associated with the second syndrome are indicated by the italic numerals.
The metabolic scheme of glycogen metabolism and glycolysis shows the ten sites at which specific enzyme defects affecting muscle, either alone or in association with other tissues, have been documented.
Traditionally, glycogen storage diseases (GSD) have been labeled with Roman numerals, more or less in the order in which they were described: GSD I, glucose-6-phosphatase; GSD II, acid maltase (Pompe's disease); GSD III, debrancher (Cori-Forbes' disease); GSD IV, branching enzyme (Andersen's disease); GSD V, myophosphorylase (McArdle's disease); GSD VI, liver phosphorylase (Hers' disease); GSD VII, phosphofructokinase [PFK] (Tarui's disease); GSD VIII, phosphorylase b kinase [PHK]; GSD IX, phosphoglycerate kinase [PGK]; GSD X, phosphoglycerate mutase [PGAM]; GSD XI, lactate dehydrogenase [LDH]; GSD XII, aldolase A [ALD]; GSD XIII, beta-enolase.
The best way to detect patients is through histochemical (GSD V and GSD VII) or biochemical (all GSD) determinations of enzyme activities.
Enzyme activities are determined spectrophotometrically by measuring NAD(H) or NADP(H) reduced (or oxidized) produced by the enzyme being tested or indirectly by associated enzyme reactions.
Muscle specimens (ideally 500 mg; minimal 200 mg) should be flash-frozen at the time of biopsy and kept in liquid nitrogen or deep freezer (-80°C) until shipped.
Specimens (in plastic containers or wrapped in aluminum foil) should be shipped in styrofoam boxes in abundant dry ice by overnight courier.
The muscle should be snap frozen in liquid nitrogen and shipped frozen on dry ice by overnight carrier to:
Dr. Ali Naini
Laboratory of Melocular Neurogenetics
Columbia University Medical Center
Department of Pathology
630 West 168th Street, P&S 17th Floor, Room 401
New York, NY 10032
82657 and 83912 (for CPT radioactive assay: 82658 and 83912)
$125 per enzyme (CPT radioactive assay is $200).