Ataxia telangiectasia (A-T) is a rare devastating human recessive disorder characterized by progressive cerebellar ataxia, immunodeficiency, chromosomal instability, and cancer susceptibility. In addition to that, a high percentage of patients show dystrophy, growth retardation and poor weight gain. Nevertheless, there are only a few studies assessing this problem. Aim of the present proposal is to investigate the exact body composition, manual muscle strength and hormonal status in patients with A-T compared to healthy controls matched for gender and age. A pelvic sonography in females was performed in order to evaluate the sexual maturity of their inner genitalia. Tanner score was determined to define the physical development. Every subject received a nutritional diary to review its calorie intake and the quality of diet. The investigators expect that the A-T cohort shows an altered body composition, impaired muscle strength, changed hormonal status concerning the sexual hormones and a delayed physical development compared to healthy controls.