<prompt> Defective DNA repair is seen in -Tuberous sclerosisAtaxia telangiectasiaVon Hippel Lindau diseaseNeurofibromatosi 1  <response>: Ans. is b i.e., Ataxia telangiectasiaAtaxia telangiectasiao Ataxia Telangiectasia AT is an autosomal recessive disorder. It is due to mutation of AT gene located on chromosome 11. There is defective DNA repair that results in multiple chromosomal breakso Patients present in first decase of life. Features are : -i Oculocutaneous telengiectasiaii Neurological - Ataxia, dysarthria, extensor plantar response, myoclonic jerks, areflexia, distal sensory deficity.iii Immunodeficeincy-Thymichypoplasiawithcellularandhumoral IgAandIgG2 immunodeficeincy.iv Recurrent pulmonary infectionsv Endocrine disorders- Tye I DMvi Premature agingvii Malignancies ? Lymphoma, Hodgkins disease, acute T cell leukemia, breast cancer. 