This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Biology, Subject name: Biochemistry
In SCID, what type of DNA repair is defective? 
Select and explain. 
A. Double strand break repair, B. Nucleotide excision repair, C. End Joining Repair, D. Mismatch repair
C: End Joining Repair
Answer: C: End Joining Repair 
Explanation: Defects in Double-Strand Break Repairs: Defects in Single-Strand Break Repairs: Non-Homologous End Joining Repair (NHEJ) SCID (Severe Combined Immunodeficiency Disease) (RS-SCID) Radiation sensitive Severe Combined Immunodeficiency Disease Nucleotide excision Repair (NER) Xeroderma Pigmentosa Homologous Repair (HR) Bloom syndrome Werner syndrome Breast cancer Base Excision Repair (BER) MUTYH associated Polyposis Mismatch Repair (MMR) HNPCC (Hereditary Non-Polyposis Colorectal Cancer)