This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Genetic Basics Of Carcinogenesis, Subject name: Pathology
All of the following are true about syndrome with microsatellite instability, except: 
Select and explain. 
A. DNA repair defects, B. Autosomal dominant, C. Increased risk of malignancy, D. May be associated with immunodeficiency
D: May be associated with immunodeficiency
Answer: D: May be associated with immunodeficiency 
Explanation: Microsatellites are tandem repeats of one to six nucleotides found throughout the genome. In normal people the length of these microsatellites remains constant. Hereditary nonpolyposis colon cancer (HNPCC) syndrome (also known as Lynch syndrome) is an autosomal dominant disorder with defective mismatch repair genes. The most commonly affected genes are MSH2 and MLH1, each accounting for approximately 30% of HNPCC syndrome. If mismatch repair is defective, microsatellites are unstable (microsatellite instability) and increase or decrease in length, creating mutated alleles. These mutations increase risk of malignancy such as colon cancer. Not associated with immunodeficiency. Ataxia telangiectasia syndrome (ATM gene) is characterized by neurodegeneration, ataxia, immunodeficiency, hypersensitivity to radiation and predisposition to cancer.