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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

Paediatric Endocrinology Section (R.S., D.D.M., M.B.R.), University Hospital for Children and Adolescents, D-72076 Tübingen, Germany; and Children’s Hospital (E.S.), University of Cologne, D-50924 Cologne, Germany

Address all correspondence and requests for reprints to: Roland Schweizer, M.D., Pediatric Endocrinology Section, University Hospital for Children and Adolescents, Hoppe Seyler Strasse 1, D-72076 Tuebingen, Germany. E-mail: Roland.Schweizer{at}med.uni-tuebingen.de.

Background: 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.

Aim: Our aim was to investigate muscle-fat distribution and muscle function before and during GH treatment in short SGA children.

Patients: 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.

Methods: Investigations over 24 months on GH treatment (57 µg/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.

Results: 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 -height SDS during the first year of GH treatment (R = –0.40; P < 0.001).

Conclusions: 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.