COMPARATIVE EXPRESSION ANALYSIS OF HUMAN ENDOGENOUS RETROVIRUS ELEMENTS IN PERIPHERAL BLOOD OF CHILDREN WITH SPECIFIC LANGUAGE IMPAIRMENT
Minchev DS1,2,*, Popov NT3, Naimov SI1, Minkov IN4, Vachev TI1
*Corresponding Author: Assistant Professor Danail S. Minchev, Department of Medical Biology, Faculty of Medicine, Medical University-Plovdiv, 4000, Plovdiv, Bulgaria. Tel: +359-896-313-627. E-mail: dante17@abv.bg
page: 49

INTRODUCTION

The term “specific language impairment (SLI)” describes a condition affecting children’s communication skills that are not caused by any organic damage of the brain, vocal apparatus and sensory systems, or by a pervasive disorder or another type of mental developmental disability [1]. Non-verbal intellectual capacity of the children with SLI is never altered in any way. This condition is relatively common, around 7.0% of the children in pre-school age are diagnosed with SLI [2]. The etiology of SLI has still not been fully elucidated. Many researchers suggest the involvement of genetic and environmental causes. Twin studies have shown that SLI is a condition with a strong genetic basis [3]. Currently, numerous molecular genetic studies, including, gene expression, candidate gene association analyses and genome-wide association studies (GWAS) have identified particular genes and chromosomal loci associated with the disease state, forkhead box Š2 (FOXP2) and contactin-associated protein 2, (CNT NAP2) on chromosome 7; calcium-transporting ATPase 2C2 (ATP2C2), and C-MAF inducing protein (CMIP) on chromosome 16 [4-8]. From another point of view, human endogenous retrovirus elements (HERVs) are known to be associated with many neuropathological and non-neurological diseases with complex etiologies, such as autism, multiple sclerosis, schizophrenia and different types of cancer. Human endogenous retrovirus elements have derived from ancient infectious retroviruses that, in many particular evolutionary stages, had integrated into the genome of the germline cells of our ancestors in evolution and started to be conveyed in a vertical fashion through many generations. At present, about 8.0% of the human genome is occupied by endogenous retrovirus elements [9]. The HERVs are composed of two long terminal repeats (LTRs) and four genes, gag, pol, pro and env. The gag gene encodes a group-specific antigen that serves as a retroviral capsid protein. Another gene, pro, codes for the viral protease, while pol contains a reverse transcriptase coding region. A HERV element differs from other LTR retrotransposons by the presence of the env gene encoding viral membrane proteins. Long terminal repeats contain many regulatory elements such as promoters, enhancers and polyadenylation signals required for retroviral gene expression [10,11]. All human endogenous retroviruses nowadays are transposition-incompetent and carry various deletions. Despite the absence of apparent transposon activity, HERVs are classified as transposons based on the evidence of transposition during the past human evolution and on the existence of several animal ERVs that have retained their mobility within the host genomes [10,12,13]. Human endogenous retroviruses are divided into families, predominantly depending on the primer binding sites, sequences complementary to the 3’ end of a cell tRNA. For example, HERV-K and HERV-W indicate that tRNALys and tRNATry are used as reverse transcription primers, respectively. This terminology is not related to the chronology of their discovery or their functions in the human genome [10,14-16]. To date, HERV expression profiles have never been studied in patients with SLI. This study aims to elucidate differentially regulated human endogenous retroelements in peripheral blood of children with SLI, in comparison with healthy controls, through quantitative reverse transcription- polymerase chain reaction (qRT-PCR) methodology.



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