Muscle Function Improves during Growth Hormone Therapy in Short Children Born Small for Gestational Age: Results of a Peripheral Quantitative Computed Tomography Study on Body Composition

Abstract

Short small for gestational age (SGA) children can be affected by a lack of muscle mass rather than fat mass. They also face a high risk of the metabolic syndrome developing after childhood. It is not known whether low muscle mass influences muscle function. Our aim was to investigate muscle-fat distribution and muscle function before and during GH treatment in short SGA children. A total of 34 prepubertal short SGA children (11 females, seven with Silver-Russell syndrome) were included in the study. Mean values were: age at GH start 7.3 yr; height sd score (SDS) -3.3; and birth weight SDS -2.7. Investigations over 24 months on GH treatment (57 microg/kg.d) were performed. Body composition, including fat area and muscle area (MA), was assessed through peripheral quantitative computed tomography (XCT 2000; Stratec, Inc., Pforzheim, Germany). Maximal isometric grip force was performed with a Jamar dynamometer (Preston, Jackson, MI). Comparison with height-dependent reference values (SDS(Height)) was calculated. MA SDS(Height) at GH start was -1.8 and increased to -0.8 (P < 0.001) and -0.8, and fat area SDS(Height) decreased from -0.6 to -2.0 (P < 0.001) and -1.5 after 12 and 24 months on GH. Maximal isometric grip force SDS(Height) increased from -0.9 to 0.3 (P < 0.001) and 0.5. MA at start correlated negatively with height velocity (R = -0.54; P < 0.001) and MA SDS at start and Delta-height SDS during the first year of GH treatment (R = -0.40; P < 0.001). Short stature in SGA children is associated with low muscle mass and function. Supraphysiological GH doses led to a concomitant increment in height, muscle mass, and function, whereas fat mass decreased. Furthermore, body composition at GH start gives insight into GH responsiveness and the individual risk of metabolic syndrome.