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
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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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