Exercise capacity and muscle structure in kidney recipient and twin donor

Exercise capacity and muscle function are known to be abnormal in patients with renal disease. We present a case study in which we studied a kidney transplant recipient who received a kidney from his identical twin. Testing included maximal exercise testing with measurement of oxygen uptake (VO2max), isokinetic muscle function testing, body composition analysis using dual energy X-ray absorptiometry (DEXA) imaging and quality of life using The Medical Outcomes Short Form (SF-36) questionnaire. Muscle biopsies were also analysed for fibre composition and size and ultrastructure. We found that the twin recipient had lower values for VO2max, muscle strength, muscle mass and quality of life scales (physical domains) compared with the twin donor. Muscle fibre composition was identical in the twins, however, muscle fibres size was reduced in the twin donor in Type I, and Type IIA fibre types. The twin recipient also showed lower fibre density (volume percentage) and greater intrafibrillar space than the donor. The twins were both sedentary, thus we conclude that the low exercise capacity and abnormalities observed in the recipient are characteristics of renal failure, and not the result of physical deconditioning, nor was it related to prednisone therapy, which may negatively affect muscle function.