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Introduction
Published in Victor A. Bernstam, Pocket Guide to GENE LEVEL DIAGNOSTICS in Clinical Practice, 2019
Type II repetitive sequence families are composed of microsatellites, or simple sequence repeats (SSR) such as (T)n/(A)n, (G)n/(C)n, (TA)n, (CA)n, (TG)n, (GC)n, (TC)n, (GGA)n, (GCA)n, and minisatellite sequence families such as (TTTTA)n and (TTAGGG)n. Certain similarities have been detected in comparing the structure of repetitive sequences such as Alu and L1, belonging to the short interspersed repeat (SINE) family in human DNA, with those of retroviral elements and transposons. The highly conserved nature of tandemly repeated DNA sequences is apparently associated with specific, apparently regulatory, and so far not fully disclosed, functions in the genome. Definite tissue-specific changes in repetitive DNA have been observed during the developmental process.
Human Immunodeficiency Virus and Tuberculosis Co-Infection
Published in Peter D O Davies, Stephen B Gordon, Geraint Davies, Clinical Tuberculosis, 2014
A critical consideration in appreciating the drivers of the HIV/TB epidemic, and in the design and implementation of effective preventative measures and allocation of appropriate resources, is an understanding of whether incident cases are a result of exogenous reinfection or endogenous reactivation. Molecular techniques such as restriction fragment length polymorphism (RFLP) typing, spoligotyping and mycobacterial interspersed repeat unit-variable number tandem repeat (MIRU-VNTR) typing have allowed insights into the transmission dynamics of M. tuberculosis (MTB) among HIV-infected patients. In a study from India in which DNA typing of initial and recurrent MTB isolates was undertaken, 88% of recurrences in HIV-infected persons were due to reinfection with a different strain [18]. In contrast, their HIV-infected counterparts experienced reinfection in only 9% of cases. A study in HIV-positive gold miners from South Africa also found reinfection in 69% of relapses [19]. Thus, ongoing transmission is likely to be the most significant cause of new TB infection in HIV-infected persons, and strategies for curbing new infections need to focus on infection control measures, providing secondary isoniazid preventive therapy (IPT), actively searching for subclinical disease and ensuring rapid institution of therapy [20].
Restoration of dystrophin expression and correction of Duchenne muscular dystrophy by genome editing
Published in Expert Opinion on Biological Therapy, 2021
Tejal Aslesh, Esra Erkut, Toshifumi Yokota
CRISPR/Cas9 is a strategy deployed by bacteria wherein viral DNA segments incorporated into the bacterial genome and transcribed into RNA serve as a guide for the Cas9 endonuclease to recognize and destroy the viral pathogen in the future [12]. There are 6 different classes of CRISPR systems (I–VI), depending on the type and number of endonucleases used [13]. Class II is the system adapted for genome editing in research settings, and it comprises of: tracrRNA (transactivating CRISPR RNA)Cas9 endonuclease (which cleaves the target 3 nucleotides from a protospacer adjacent motif (PAM))CRISPR array made up of interspersed repeat elements along with spacer elements made from viral phage DNA that serves as a memory to fight phage infections in the future.