According to our results every second child with FASD experiences sleep disorders. This finding is consistent with the result of the research published by Goril et al.(15) who estimated the prevalence of sleep disorders among individuals with FASD to 58%. On the other hand, Chen et al.(16) established a prevalence rate at 85%. Although similarly to our study, Chen et al. used the CSHQ, they classified children with the borderline Total Score of 41 as having sleep disturbances whilst we, following the CSHQ instruction(12, 17), qualified only the children who scored above 41. However, 7 children from the FASD group (17.5%) and 7 children from the control group (17.5%) had a Total score equal with 41. The subscales revealed that sleep onset delay, night wakings, parasomnias, sleep disordered breathing and daytime sleepiness occur more frequently among individuals with FASD. The trend, although without statistical significance, was also observed regarding sleep anxiety and bedtime resistance. These results are in agreement with those obtained by Chen et al.(16) who reported an increased frequency of sleep problems in all 8 subdomains of CSHQ. Our observations are also in line with the findings reported by Wengel et al. who indicated that patients with FASD complained about bedtime resistance, shortened sleep duration, sleep anxiety, night awakenings and parasomnias.(18)
The data on the results of the polysomnography among FASD patients is scarce. Our findings match those published by Chen et al.(16) although we observed that not only obstructive but also central apneic events were more frequent among individuals with FASD. However, as the authors suggested, given the small sample size, their data should be considered exploratory. Similarly, Goril et al.(15) indicated an increased sleep fragmentation and an increased predisposition to apneic/hypopneic events, interestingly, the increased AHI was only observed in the young children in their sample. Alvik et al., Troese et al. and Scher et al(19–21) demonstrated that infants with prenatal alcohol exposure tend to present fragmented sleep and experience more arousals, however, these studies were performed with a different methodology. A similar finding was documented by Volgin et al. on an animal model of PAE.(22) In our study sleep in FASD subjects was less stable than in the control group which is mainly expressed in a greater number of stage shifts, an increased amount of stage N1 and a higher number of arousals. The lack of relation between arousals and breathing events suggests that the subset of arousals has other than a respiratory cause. Interestingly, in comparison to general population samples(23, 24) (Table 4) the results are not consistent. Montgomery Downs reported the amount of N1 sleep higher than in our subjects but Goodwin reported it approximately at the same level. The amount of N3 is comparable to the Montgomery-Downs sample but much higher than in the Goodwin sample. The percentage of REM sleep is the lowest in our FASD group in comparison to both studies. The amount of this stage is also lowered in our control groups, so the proportion of laboratory related and FASD related factors is difficult to be examined. However, insufficiency of REM sleep is one of the major causes of neurocognitive problems. The number of arousals is lower in comparison to both studies.
Both examined groups (FASD and control) had much more detected breathing events than reported in general population samples. It is clearly visible in all compared indices (Table 4), however for some of them (hypopnea index) it could be a combined result of our groups characteristics and differences in the scoring criteria. The changes in the hypopnea definition which were introduced in version 2 of AASM manual lead to an increased number of detected events. According to the authors’ knowledge there is no information about how those changes affect hypopnea index results in children population but the hypopnea index in our study is larger by an order of magnitude which is more than a potential impact of definition changes. The central apnea index in the FASD group is greater by factor of two, even though current children central apnea definition is more restrictive. The cause of sleep problems among individuals with FASD remains uncertain. Chen et al. suggested, using the rat model, that PAE affects expression of the genes responsible for the circadian function of β-endorphin neurons in the hypothalamus.(25) On the other hand, Goril et al. determined that children with FASD have an altered melatonin profile, which can affect the sleep cycle.(15) The central apneic/hypopneic events result from the central nervous damage secondary to prenatal alcohol exposure, as it has been established that alcohol affects the neurons in the variety of modes. (26) It is worth mentioning that obstructive apneic/hypopneic events were frequent among children with FASD, however, none of the patients was obese. Nevertheless, the anatomical features connected to FASD – micrognathia, high-arched palate may result in the airway obstruction.(27, 28)
This is the first study to comprehensively assess the sleep problems among children with FASD in a relatively big sample with a control group. Due to organizational reasons the enrollment to the both groups was performed simultaneously which resulted in the negligible age difference between the groups. However, patients from both groups were within the age frame for CSHQ (3–18 years) and all differences observed between the groups were independent of age. CSHQ is a subjective sleep problems assessment which might be considered a limitation of this study. Only the patients screened by CSHQ were offered the objective sleep evaluation. The majority of parents in the study group were either foster or adoptive parents yet, the patients from the control group were in biological families. It is well established that foster and adoptive parents of FASD children experience a lot of distress and they present a tendency to an overprotective attitude(29) which can be a potential source of bias in the self-report. Moreover, the 3 patients from the study group and 3 from the control group withdrew their consent and discontinued the study after the invitation to the second phase of the study. However, even with this limitation many patients completed the PSG and the results can be considered representative.
Notwithstanding the limitations, the study offers the overview of the frequency and nature of sleep problems among individuals with FASD. Further experimental investigations are needed to determine the mechanisms that contribute to this phenomenon as well as the treatment options. From the clinical perspective it is important for the physicians and psychologist taking care for patients with FASD to include the question about the sleep quality in the history taking and try to address this issue.