Summary Background & aims Different neuromuscular functional domains in types I and II Spinal Muscular Atrophy (SMAI and SMAII) could lead to differences in body composition (BC) and resting energy expenditure (REE). Their identification could provide the key to defining appropriate strategies in clinical dietary management, but data comparing SMAI and SMAII in terms of BC and REE are not yet available. We measured total and regional fat (FM), lean (LBM), mineral (BMC) masses, body water (total, intra- and extra-cellular, TBW, ICW, ECW) and REE in a sample of SMAI and II children, matched for age and sex, and also adjusting for body size to compare these features of the two SMA phenotypes. Methods 15 SMAI and 15 SMAII children, (M/F = 9/6 vs 9/6, age 3.6 ± 1.9 vs 3.5 ± 1.8 years, p = 0.99), confirmed genetically, were measured as follows: Anthropometric measurements [Body Weight (BW), Supine Length (SL), Arm Length (AL), Femur Length (FL), Tibia Length (TL)], Dual x-ray Energy Absorptiometry (DEXA) [total and segmental FM, LBM, FFM, and BMC], Bioelectrical impedance (BIA) [TBW, ICW, ECW] and Indirect Calorimetry (REE, respiratory quotients) were collected by the same trained dietician. BW, SL and Body Mass Index (BMI) Z-scores were calculated according to CDC Growth Charts (2000). Results SMA children had high percentages of FM and a lower percentage of TBW and ECW compared to the respective reference values for sex and age, whereas the BMC percentages did not differ, even splitting the two phenotypes. SMA I children had a lower BW and BMI-Z score compared to children with SMA II, but similar total and segmental FM. On the contrary, total FFM and LBM were significantly lower in SMAI (7290.0 ± 1729.1 g vs 8410.1 ± 1508.4 g; 6971.8 ± 1637.1 g vs 8041.7 ± 1427.7 g, p = 0.039, p = 0.037, respectively), particularly at the trunk level. Arm BMC also resulted significantly lower in SMAI. The measured REE values were similar (684 ± 143 kcal/day vs 703 ± 122 Kcal/day p = 0.707) whereas REE per FFM unit was higher in SMA I children than in SMA II (95 ± 12 kcal/FFMkg vs 84 ± 11 kcal/FFMkg p = 0.017). Conclusions This study has shown that BW and BMI Z-score measurements alone can be misleading in assessing nutritional status, particularly in SMAI. The differences between SMAI and II in total and regional BC are related only to FFM, LBM and BMC, and seem to be more linked to the magnitude of neurofunctional impairment rather than to the nutritional status derangement. SMA I and SMA II children can have different energy requirements in relation to their specific BC and hypermetabolism of FFM. Based on these results, our recommendation is to use direct BC and REE measurements in the nutritional care process until SMA-specific predictive equations become available.

中文翻译：

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脊髓性肌萎缩症，I 型和 II 型：身体成分和静息能量消耗有何不同？

摘要背景和目标 I 型和 II 型脊髓性肌肉萎缩症（SMAI 和 SMAII）中不同的神经肌肉功能域可能导致身体成分 (BC) 和静息能量消耗 (REE) 的差异。它们的鉴定可以为在临床饮食管理中定义适当的策略提供关键，但在 BC 和 REE 方面比较 SMAI 和 SMAII 的数据尚不可用。我们测量了 SMAI 和 II 儿童样本中的总和区域脂肪 (FM)、瘦肉 (LBM)、矿物质 (BMC) 质量、体水（总、细胞内和细胞外、TBW、ICW、ECW）和 REE，匹配年龄和性别，并调整体型以比较两种 SMA 表型的这些特征。方法 15 名 SMAI 和 15 名 SMAII 儿童（M/F = 9/6 vs 9/6，年龄 3.6 ± 1.9 vs 3.5 ± 1.8 岁，p = 0.99），经基因证实，测量如下：人体测量学测量 [体重 (BW)、仰卧长度 (SL)、臂长 (AL)、股骨长度 (FL)、胫骨长度 (TL)]、双 X 射线能量吸收仪 (DEXA) [总和分段 FM、LBM 、FFM 和 BMC]、生物电阻抗 (BIA) [TBW、ICW、ECW] 和间接量热法（REE，呼吸商）由同一位训练有素的营养师收集。BW、SL 和体重指数 (BMI) Z 分数是根据 CDC 增长图表 (2000) 计算的。结果与性别和年龄的参考值相比，SMA儿童的FM百分比较高，TBW和ECW百分比较低，而BMC百分比没有差异，甚至将两种表型分开。与 SMA II 儿童相比，SMA I 儿童的 BW 和 BMI-Z 评分较低，但总和分段 FM 相似。相反，SMAI 中的总 FFM 和 LBM 显着降低（7290.0 ± 1729.1 g vs 8410.1 ± 1508.4 g；6971.8 ± 1637.1 g vs 8041.7 ± 1427.7 g，分别为 p = 0.039，p = 0.037），尤其是在躯干水平。Arm BMC 的 SMAI 也显着降低。测量的 REE 值相似（684 ± 143 kcal/天 vs 703 ± 122 Kcal/天 p = 0.707），而 SMA I 儿童每 FFM 单位的 REE 高于 SMA II（95 ± 12 kcal/FFMkg vs 84 ± 11千卡/FFMkg p = 0.017)。结论 本研究表明，单独的 BW 和 BMI Z 评分测量在评估营养状况时可能会产生误导，特别是在 SMAI 中。SMAI 和 II 在总和区域 BC 中的差异仅与 FFM、LBM 和 BMC 有关，并且似乎与神经功能障碍的程度有关，而不是与营养状况紊乱有关。SMA I 和 SMA II 儿童可能有与其特定的 BC 和 FFM 高代谢相关的不同能量需求。基于这些结果，我们的建议是在营养保健过程中使用直接的 BC 和 REE 测量，直到 SMA 特定的预测方程可用。