Hypermetabolic Levels of Protein Turnover and Energy Expenditure in Bloom's Syndrome 735

Bloom's syndrome is a rare autosomal recessive disorder characterized by elevated frequency of sister chromatid exchange, increased risk for malignancies, and normally proportioned short stature. However, no studies have evaluated the possibility of hypermetabolism and increased macronutrient requirements in these patients. Therefore, we measured protein kinetics and energy expenditure in a child (B.P.) with Bloom's syndrome and compared the results with published reports of hyper- metabolic children of similar age with acute, large body-surface-area burns.

Methods: Protein kinetics were determined using primed, constant infusions of ¹³C-leucine and ¹³C-NaHCO₃ while feeding hourly amounts of Pediasure®. Sleeping and awake energy expenditure were determined by indirect calorimetry and by calculation of CO₂ production from ¹³C-breath analysis, respectively. Body fat% was determined by total body electrical conductivity (TOBEC).

Results: Despite measured intakes on three occasions of 180-230 kcal/kg/d and 5.4-6.5 g-protein/kg/d between 9 and 17 months of age, B.P. weighed only 6.1 kg at 17 months of age (50%-ile for a 3 month-old infant). Length was 66 cm (50%-ile for a 5 month-old infant), and total body fat was only 9% of body weight. In comparison to acutely burned children, B.P. demonstrated significantly elevated levels of leucine oxidation (129vs. 59 ± 9 μmol/kg/hr) and decreased levels of non-oxidative leucine disposal (i.e., protein synthesis, 178 vs. 231± 31 μmol/kg/hr) and protein balance (0.4 vs. 1.1 ± 0.5 g-protein/kg/d). B.P. also had a similar total leucine flux (308vs. 290 ± 38 μmol/kg/hr) and leucine flux from endogenous protein breakdown (169 vs. 208 ± 35 μmol/kg/hr). Sleeping energy expenditure (70.0 kcal/kg/d) and awake energy expenditure (85 kcal/kg/d) were elevated compared to age-predicted basal energy expenditure(127% and 154% of BEE, respectively) and within the range seen in burned children.

Conclusion: Bloom's syndrome patients may be hypermetabolic, manifested by elevated protein turnover and leucine oxidation, poor protein balance, and increased energy expenditure. Thus, these patients may possess increased macronutrient needs which may even surpass those of patients with acute burn injuries.