A transcript coding for a partially duplicated form of α7 nicotinic acetylcholine receptor is absent from the CD4+ T-lymphocytes of patients with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE)

Introduction: It has been suggested that the homomer-forming alpha 7 subunit (CHRNA7) of the neuronal nicotinic acetylcholine receptor (nAChR) is involved in the pathogenesis of common idiopathic generalized epilepsies (IGEs), whereas mutations of the gene coding for the alpha 4 nAChR subunit (CHRNA4) are associated with autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). Several genes encoding nAChR subunits, including a partially duplicated isoform of CHRNA7 (CHRFAM7A), are expressed in peripheral blood lymphocytes (PBLs), and are constituents of peripheral receptors corresponding to nAChRs in the brain. Moreover, a 2-bp deletion polymorphism (c.497-498delTG; rs67158670), resulting in a frame shift and truncation of the protein product of the gene, has been found in the CHRFAM7A gene and is associated with some neurological diseases. Aim of the study: CHRFAM7A transcript levels in CD4(+) T-lymphocytes were compared between ADNFLE patients harbouring the c.851C>T mutation of the CHRNA4 gene and control healthy individuals in order to determine whether there is any correlation between CHRFAM7A expression in CD4(+) T-lymphocytes and the severity of epileptic symptoms. We also tested the hypothesis that the 2-bp deletion polymorphism in the partially duplicated alpha 7 nAChR gene may be related to ADNFLE in these patients. Material and methods: Peripheral venous blood samples were collected from 3 individuals with ADNFLE and from 10 healthy individuals. From the isolated CD4(+) T-lymphocytes, RNA was prepared and the CHRFAM7A transcript level was determined by RT-qPCR. In order to compare the CHRNA7 and CHRFAM7A sequences and genotype the -2bp polymorphism, genomic DNA was prepared from PBLs. Results: It has been demonstrated that CHRFAM7A is expressed in CD4(+) T-lymphocytes of healthy individuals, the relative abundance of the transcript being nearly equal (about 100 copies per cell), but it is not expressed in ADNFLE patients. Genotype analysis showed that the -2bp polymorphism was found in all patients as well as in seven healthy individuals. Conclusions: Our observations confirm the hypothesis that the CHRFAM7A gene is expressed in CD4(+) T-lymphocytes of healthy individuals and that this expression is legitimate. The observed lack of CHRFAM7A expression in ADNFLE patients might be an important factor in the pathogenesis of ADNFLE.