Despite a recent significant expansion of our understanding of sleep and sleep disorders, our knowledge of how these advancements pertain to adults with ID remains limited [3]. Sleep disorders in adults with ID are often referred in the literature under different terminologies, such as behavioural sleep problems, which may encompass any sleep disorder from insomnia to narcolepsy [4]. Despite internationally recognised diagnostic categories and criteria, it reflects the limited advancement of sleep medicine in this population. Diagnostic overshadowing, where clinicians may attribute a sleep disorder to being part of a person’s intellectual disabilities, rather than recognising and treating it as a separate entity [5] further affect appropriate support for individuals experiencing sleep problems. Therefore, diagnostic methods and treatments of sleep disorders in adults with ID is extrapolated from the evidence base in adults without ID, except for specific studies looking at certain sleep disorders in specific genetic conditions.

Below, we summarise the current understanding of common sleep disorders in adults with ID.

Insomnia is more common in adults with ID when compared to the general population [6]. One of the reasons underlying this, may be that adults with ID experience more fragmented sleep [7]. There is also growing evidence that risk of sleep disturbance increases with the severity of the ID [8, 9]. It is likely that sleep problems are only reported when they become a challenge to caregivers, especially in those individuals who cannot communicate their sleep-related night- and day- time dysfunction. There are no specific guidelines for diagnosing Chronic Insomnia Disorder in this cohort.

Cognitive Behavioural Therapy for Insomnia (CBT-I) is the first line treatment recommended by UK national [10], as well as international sleep medicine guidelines [11]. There is some evidence that a modified CBT-I approach is helpful for adults with ID [12]. Focusing on sleep scheduling has been successfully demonstrated, either on its own or as part of a multi-modal CBT-I approach for adults with ID. In this technique, the average total sleep time (obtained from sleep diaries and/or actigraphy) is aligned to the average total time in bed, usually measured over 1–2 weeks. This has been shown to optimise the homeostatic sleep drive, thereby consolidating sleep, and reducing hyperarousal. This technique requires caregiver education and flexibility, as often adults with ID have early bedtimes imposed on them i.e. they are ‘put to bed’ before their homeostatic sleep drive is sufficiently high enough to induce and/or maintain sleep. Sleep scheduling should be supervised by a behavioural sleep medicine specialist, as any unintended sleep loss may worsen physical (e.g. epilepsy) and mental (e.g. bipolar affective) disorders. Moreover, if a sleep diary is completed by a caregiver (as opposed to the individual with ID), there may be reporting errors, such as a lower estimate of wake-after-sleep-onset time (a measure of sleep maintenance) [13]. Additional CBT-I techniques are outlined in Table 1.

Optimising scheduled daytime activities and sleeping environments can also significantly improve sleep in this population. For example, it has been reported that adults with ID attain less daily exercise, have relatively unhealthy diets, and reduced access to structured daytime activities when compared to the general population [12].

The pharmacological treatment of Chronic Insomnia Disorder in adults with ID tends to follow the same treatment guidelines as those for the general population. There is again a paucity of research in this area, with melatonin receiving the most attention on account of its favourable side-effect profile. One meta-analysis concluded that in individuals with intellectual disabilities, the use of melatonin decreases sleep onset latency (i.e. the time taken to get to sleep), decreases the number of awakenings per night, and increases the total sleep time [14]. Despite the growing evidence base for pharmacological treatments, as far as we are aware, none of these studies include people with ID.

Little is known about the prevalence of sleep breathing disorders in adults with ID, with one notable exception, i.e. Obstructive Sleep Apnoea (OSA) in adults with Down syndrome (DS) [15], where prevalence rates of up to 100% have been reported [16]. Adults with DS are at increased risk of OSA because of the characteristic features such as cranio-facial abnormalities, hypotonia, and obesity associated with the genetic syndrome. As a result, it is recommended that everyone with DS in the UK is screened for OSA [17].

OSA in DS presents similarly to the general population, with symptoms of snoring, witnessed apnoea, nocturia, and excessive daytime somnolence as well as more atypical symptoms, including behavioural and mood disturbances [18]. This is important in the context of interventions for challenging behaviour in people with ID. Furthermore, there is evidence that optimal brain ageing is important for adults with DS, and reducing nocturnal hypoxia is important, given their increased risk of early onset Alzheimer’s dementia [19].

As with other sleep disorders, OSA symptom reports in adults with DS often rely on caregiver collateral history and observation, and it can be further complicated by diagnostic overshadowing. To aid clinician screening, the STOP-Bang questionnaire has been validated for adults with DS, who have a moderate-to-severe OSA [20]; and there is also a pictorial version of the Epworth Sleepiness Scale, which has had more variable validation success [21]. The STOP-Bang questionnaire consists of four self-reportable (STOP: snoring, tiredness, observed apnoea, and high blood pressure) and four demographic (Bang: body mass index, age, neck circumference, and gender) items [22]. Individuals with a STOP-Bang score of 0 to 2 can be classified as low risk for moderate to severe OSA, whereas those with a score of 5 to 8 can be classified as high risk for moderate to severe OSA. Individuals whose STOP-Bang scores are in the midrange (i.e. 3 or 4), require further clinical evaluation to determine the likelihood of OSA [22].

To aid diagnosis, it is generally advocated to use the least intrusive sleep diagnostic investigation, preferably undertaken in a home setting, e.g. with home pulse oximetry. If inpatient polysomnography is clinically indicated, then having access to an individual room, as well as the capacity to involve caregivers can be helpful, as can allowing extra time for equipment (e.g. electrode) acclimatation. The world of sleep diagnostics is a rapidly evolving one, and the expansion of minimally invasive and contactless sleep recording [23] hold great promise for improving SDB diagnoses in adults with ID. There may of course be times when an adult with ID cannot tolerate any clinically relevant sleep investigations, and in this scenario, a pragmatic trial of treatment may be required.

Continuous positive airway pressure (CPAP) has been demonstrated to be effective in treating adults with DS and OSA, with improvements in sleep, excessive daytime somnolence, mood, behavioural disturbance, general health and cognitive function [24]. CPAP adherence is always a challenge (regardless of the presence of ID), and encouragingly, one observational study of 75 adults with DS and OSA, demonstrated a mean CPAP concordance of > 4 h in 79% of participants [25]. A CPAP concordance of > 4 h/night is the general minimum advised treatment time in the non-ID population to attain sleep and health benefits [26]. However, using this same recommendation in the ID population may not be warranted e.g. another study of 25 adults with DS and OSA demonstrated that 2.8 h CPAP use/night over a 12-month period led to appreciable health, mood and behavioural benefits [24]. For individuals who struggle to accept CPAP, exposure therapy is considered beneficial, and in this scenario, collaborative working between sleep medicine specialists and others (e.g., mental health nurses, families, carers) can be helpful. Where positive airway pressure is unsuccessful or not tolerated, there is some evidence to support sleep surgery, such as hypoglossal nerve stimulation [27]; and where obesity plays an important aetiological role, medical management e.g. with glucagon receptor-1 agonists, can be considered [28]. Interestingly, a 10-year follow-up study of individuals with DS and OSA who underwent sleep surgery (e.g. hypoglossal nerve stimulation, adenotonsillectomy) demonstrated reduced morbidity and mortality compared to those who had not [29].

At least a third of adults with ID will experience multiple sleep difficulties [30], with older adults, and those with a higher severity of ID and/or associated physical and mental health co-morbidities at higher risk [31].

Circadian Rhythm Sleep Wake Disorders, and Sleep Movement Disorders, such as restless legs syndrome and periodic limb movements in sleep are other sleep disorders of importance in people with ID given their association with Neurodevelopmental disorders (NDDs) [32], such as Autism Spectrum Disorder (ASD) and Attention Deficit Hyperactivity Disorder (ADHD).

Other factors such as common physical health conditions, including constipation, pain, wisdom teeth eruption, and gastroesophageal reflux disease can often go unrecognised, particularly in non-verbal adults with ID, resulting in quite significant sleep disruption [31]. Certain genetic and syndromic ID disorders are also associated with specific sleep disorders e.g. circadian rhythm sleep–wake cycle inversion in Smith-Magenis Syndrome [33], hypersomnolence/narcolepsy in Prader-Willi Syndrome [34], nocturnal seizures in Angelman Syndrome [35], and early-onset dementia with sleep disturbance in Down syndrome [36]. Moreover, common mental health co-morbidities such as depression and anxiety that may present atypically in adults with ID [37], and there may be increased sensitivities to medications [38], all of which may present as a primary sleep disturbance.

There are no published sleep medicine guidelines for adults with ID on specific assessment nor treatment. We have previously proposed one approach for the screening, assessment and treatment of sleep disorders in adults with ID (Table 2 and Fig. 1) [3, 31]. In our experience, treatment plans frequently require a holistic multi-modal approach, which may in part be based on existing standard adult sleep medicine treatment guidelines.

Suggested flowchart for screening, assessment, and diagnosis of sleep disorders in adults with intellectual disability. Abbreviations: ID intellectual disability, CBT-I cognitive behavioural therapy for insomnia, GP general practitioner, MDT multiple disciplinary team. From reference [31]