Ataxia telangiectasia (Louis-Bar syndrome) - a disease with autosomal recessive mode of inheritance, occurring at a frequency of 1: 40,000 births. Disease gene mapped in 1988 on the long arm of chromosome 11 locus 11q22-11q23. LK revealed the boy, 7 years, observed at the Children's Neurological city polyclinic with complaints of epileptic seizures, delayed psycho-speech development. An example of what design of study is this disease