[Is there an interaction between sleep-disordered breathing, depression and apolipoprotein E phenotype?]

Sleep-disordered breathing (SDB) is widely underdiagnosed among adults. However, SDB may be considered as a public health problem because of clinical consequences for the patient: impaired awake performance, increased risk factor for cardiovascular diseases and increased prevalence of depression. Apolipoprotein E (apoE), a protein involved in lipid metabolism, has 3 major alleles e2, e3 and e4. Recently, it has been shown that apoE e4 allele, a well-known risk factor for cardiovascular diseases, was also associated with SDB. In this study, we assessed a potential interaction between SDB, depression and apoE phenotype. 92 male patients (36-79 years old, mean age 58.0 11.2) consulting in hospital for SDB were enrolled in the study. Each patient had the following exams: 1) overnight polysomnography to determine apnea/hypopnea index (AHI=average number of respiratory events 10 seconds with no breathing per hour). A moderate-to-severe SDB was defined with AHI 15. 2) a psychiatric examination to look for previous or present symptoms of depressive illness. 3) blood sampling to determine apoE genotype (using PCR-RFLP method). In our study, allele frequencies for apoE e2, e3 and e4 were similar to those reported in general population. Among 92 patients, 68 (74%) presented moderate-to-severe SDB and 28 (30%) previous or present symptoms of depressive illness. Our results indicate that: 1) apoE e4 was significantly associated with moderate-to-severe SDB (n=92, p=0.03), 2) scores of apnea-hypopnea index were significantly higher in e4-positive versus e4-negative participants (n=57, p=0,05) and 3) ApoE and depression were not linked. This study confirms a potential interaction between SDB and apoE phenotype, as recently reported. This suggests that e4 allele might be a genetic risk factor for SDB (e4 allele frequency higher in patients with moderate-to-severe SDB versus general population) and/or consequently a deleterious factor for this pathology (increased AHI in e4-positive versus e4-negative patients). Depression might be only one of clinical consequences of SDB. Thus, SDB leads to repeated hypoxemia and numerous awakenings resulting in fatigue and decreased cognitive abilities suitable to the onset of depressive illness in vulnerable persons.