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Hypotonia of rickets: a sequential study by P-31 magnetic resonance spectroscopy
C E Mize1, R J Corbett, R Uauy
1University of Texas Southewestern Medical Center, Department of Pediatrics, Dallas 75235-90063.
Insights
Vitamin D-dependent rickets treatment improved muscle strength by restoring high-energy phosphorus compounds. Muscle phosphocreatine to ATP ratios increased, correlating with clinical recovery in infants.
Area of Science:
- Biochemistry
- Pediatrics
- Medical Physics
Background:
- Vitamin D-dependent rickets can cause hypotonia in infants.
- The role of high-energy phosphorus compounds in this condition is not fully understood.
Observation:
- Nuclear magnetic resonance (NMR) spectroscopy was used to study muscle metabolism in an infant with rickets.
- Measurements were taken during treatment with vitamin D, calcium, and phosphorus.
Findings:
- Muscle hypotonia resolved before radiographic signs of healing.
- The ratio of phosphocreatine to beta-adenosine triphosphate [PCr/beta-ATP] in muscle increased significantly during treatment.
- This ratio approached levels seen in healthy infants and adults.
Implications:
- The recovery of muscle strength appears linked to the restoration of high-energy phosphate compounds.
- NMR can provide insights into the metabolic basis of rickets recovery.
- These findings highlight the importance of phosphorus metabolism in muscle function during rickets treatment.
Abstract:
To address the role of high-energy phosphorus compounds in the hypotonia of vitamin D-dependent rickets, nuclear magnetic resonance spectra were obtained sequentially from resting gastrocnemius muscle of a 10-month-old infant with rachitic hypotonia during supplementation with vitamin D, calcium, and phosphorus. During the initial weeks of treatment, the hypotonia resolved before evidence of epiphyseal mineralization. Over the early treatment period, the muscle phosphocreatine/beta-adenosine triphosphate [PCr/beta-ATP] ratio increased from 2.7-2.8 [wk 1-2] to 3.9-4.5 [wk 7-9]. The PCr/beta-ATP ratio for 6-month-old normal infant gastrocnemius and adult forearm were 4.0 and 5.7, respectively. Muscle strength appeared to recover concomitantly with an increase in retained muscle phosphorus and high-energy phosphate compounds, and with relative increase in the muscle phosphocreatine to ATP ratio. The synchrony of clinical recovery may relate to the recovery kinetics of these metabolic changes.