Association of GABA B R1 Receptor Gene Polymorphism with Obstructive Sleep Apnea Syndrome

1. Association of GABABR1 Receptor Gene Polymorphism with Obstructive Sleep Apnea Syndrome Oğuz Köktürk*, Tansu Ulukavak Çiftçi*, Yıldırım A. Beyazıt**, Metin Yılmaz**, M.Emin Erdal*** * Gazi Ü. T. F. Göğüs Hastalıkları A. D., ** Gazi Ü. T. F. KBB A.D., ***Mersin Ü. T. F. Tıbbi Biyoloji ve Genetik A.D.

2. Introduction and Aim • GABA (gamma-amino-butyric acid) is one of the most common neurotransmitters in the CNS. It might be functionally important in cortical disinhibition. • The GABA receptors in the brain have been classified into: • GABAAR ve GABABR • GABABR, inhibits cAMP formation and inositol phosphate turnover. There are 2 forms: • GABABR1a ve GABABR1b

3. GABABR1 a and b variants are derived from the same gene: Human GABABR1 gene (chromosome 6p21.3) • The GABABR modulates synaptic transmission by presynaptic inhibition of neurotransmitter release or by postsynaptic increase of potassium conductance, which is responsible for long-lasting inhibitory postsynaptic potentials.

4. GABABR mediated neurotransmission has been implicated in the pathophysiology of a variety of neuropsychiatric disorders including obsessive compulsive disorder, schizophrenia, epilepsy and alcohol dependence. GABABR1a gene polymorphism is not known in OSAS. • Recently, three exonic GABABR1 gene variants were identified.

5. We aimed to assess significance of three different GABABR1 gene polymorphisms (A1a20Val, Gly489Ser and Phe658Phe) in OSAS.

6. Materials and Methods • 75 patients with OSAS (23 F and 52 M) (apnea-hypopnea index = AHI > 5). • 99 healthy volunteers (51 F and 48 M) • Mental retardation, drug dependence, alcoholism, somatic or neurological illnesses were exculeded. • Venous blood sample was drawn from each individual for genetical analysis.

7. Using PCR technique, the Ala20Val, Gly489Ser and Phe658Phe polymorphisms of the GABABR1 gene were analyzed in the DNA obtained from leukocytes of the patients and healthy controls.

8. Results • For Ala20Val variants: • There was no sigificant difference between the genotypes and allele frequencies of the patients and controls. • The T/T variant could not be found in both groups. • Gender specific comparisons did not reveal significant difference (F patients – F controls, M patients – M controls, F patients – M patients, F controls – M controls).

9. For Phe658Phe polymorphism: • There was no signgficant difference between the genotypes and allele frequencies of the patients and controls. • Gender specific comparisons did not reveal significant difference (F patients – F controls, M patients – M controls, F patients – M patients, F controls – M controls). • However; C/C genotype was overrepresented in M patients than F patients while T/C genotype was overrepresented in F patients than M patients (p=0.03).

10. For Phe658Phe polymorphism • There was a significant difference between the gentoypes of M patients versus M controls (p=0.024): The C/C genotype was overrepresented and the T/C genotype was less frequent in male patients than male controls.

11. For Gly489Ser polymorphism: • All of the patients and controls had G/G genotype. Therefore further statistical comparisons could not be made.

12. Statistical comparisons between the polysomnography findings and genotypes: • Ala20Val variants: the arousal index of the M patients with C/C genotype were significantly higher than in the patients with C/T genotype. • Phe658Phe variants: The %total sleep time in stage I of the M patients with T/T gentoype were significantly higher than in the patients with T/C genotype.

13. Statistical comparisons between the polysomnography findings and genotypes: • Ala20Val variants: The % total sleep time in stage II of the F patients with C/C gentoype were significantly higher than in the patients with C/T gentoype.

14. Discussion • Hypoglossal motoneurons are cholinergic elements that innervate tongue muscles and are thus important for functions such as swallowing, respiration, suckling and vocalization. • Disorders of hypoglossal motoneurons appear to be implicated in OSAS. • GABA is released within the hypoglossal motor nucleus, with individual hypoglossal motoneurons containing receptors for the neurotransmitter.

15. Under GABA derivatives, various patients had a tendency towards an increase in total sleep duration and reduction in the number of spontaneous wake-ups during night* • In another study, GABA was shown to induce a marked sedation and potentiated nitrazepam** *Vlasov NA. Effect of gamma-aminobutyric acid derivatives on sleep disorders in neuroses. Biull Eksp Biol Med 1978; 85: 174-7 . **Wambebe C. Influence of some GABAergic agents on nitrazepam-induced sleep in the domestic fowl (Gallus domesticus). Jpn J Pharmacol 1983; 33: 1111-8.

16. The GABABR1 polymorphism may affect EEG recording and be is one of the important mediators invoved in sleep. • Reciprocal interactions occur between serotonin and GABABR in CNS and serotonergic mechanisms appear to be associated with the occurrence of OSAS, especeially in M patients* *Yılmaz M, Bayazit YA, Ciftci TU, Erdal ME, Urhan M, Kokturk O, Kemaloglu YK, Inal E. Association of serotonin transporter gene polymorphism with obstructive sleep apnea syndrome. Laryngoscope 2005; 115: 832-6.

17. For Ala20Val variants: • There was no sigificant difference between the genotypes and allele frequencies of the patients and controls. • The T/T variant could not be found in both groups. • Gender specific comparisons did not reveal significant difference (F patients – F controls, M patients – M controls, F patients – M patients, F controls – M controls).

18. Ala20Val gene poymorphism is not associated with the occurence of OSAS. • These genetic variations may alter sleep efficiency. Some patients with OSAS are aware of their symptoms like arousals at night, decreased sleep efficiency and day time sleepiness whereas some others do not complain these symptoms despite abnormal polysomnography results.

19. For Gly489Ser polymorphism: • All of the patients and controls had G/G genotype, which may be representative for the population in this country. Since almost all population had the same genotype, it is plausible to say that the this polymorphism is not associated with occurrence of OSAS in this country.

20. For Phe658Phe polymorphism: • There was no significant difference between the genotypes and allele frequencies of the patients and controls. • Gender specific comparisons did not reveal significant difference (F patients – F controls, M patients – M controls, F patients – M patients, F controls – M controls). • However; C/C genotype was overrepresented in M patients than F patients while T/C genotype was overrepresented in F patients than M patients (p=0.03).

21. The Phe658Phe polymorphism is associated with occurrence of OSAS. • Especially males with the C/C genotype are highly likely to have OSAS. • This gene polymorphism seems be related to regulation of sleep in male OSAS patients.

22. Conclusion • The Ala20Val polymorphism of GABABR1 gene may be associated with symptomatology in OSAS. • The C/C variant of the Phe658Phe polymorphism GABABR1 gene seems associated with occurrence and symptomatology of OSAS, especially in male patients. • Gly489Ser polymorphism does not seem to be involved in OSAS, especially in this country.