Introduction 

Have you noticed any teenager who has been sleeping around 16 to 21 hours per day? They may suffer from Kleine-Levin syndrome (KLS). KLS is a rare neurological disorder most commonly seen in adolescents, marked by recurring episodes of extreme sleepiness. These episodes are often accompanied by unusual behaviour and cognitive disturbances. 

Teenagers are stereotypically known to experience ‘hormonal rollercoasters’ - this is mainly connected to hormonal imbalance experienced in adolescence. The main feature of KLS in these individuals is hyperinsomnia, which is excessive sleeping for hours. This condition can also include the presentation of other symptoms such as disinhibition, sometimes hypersexuality, and hyperphagia.

With years of research, we now understand that hormonal imbalances involving the hypothalamus and endocrine system play a key role in the symptoms of KLS. In this article, we explore these mechanisms, providing clarity for patients, families, and clinicians.

Understanding KLS

KLS usually presents from childhood to early adulthood. The affected individuals typically experience episodes where they sleep for 15 to 20 hours per day. These episodes can last for several days or even extend to a few weeks. 

Episodes often start suddenly, frequently following viral infections, and may persist for days or weeks. At the start of an episode, affected people can present abnormal behaviour like excessive food intake, hyperphagia and irritability, childishness, disorientation, and hallucinations. Between episodes, they typically return to normal functioning, and the frequency of episodes declines with age.¹

Though the exact cause of KLS remains unclear, research suggests a combination of factors: genetic predisposition - KLS affects individuals assigned male at birth (AMAB) more often than those assigned female at birth (AFAB)-, autoimmune involvement, and dysfunction of the hypothalamus.²

Role of the hypothalamus in regulation 

The hypothalamus, found at the base of the brain, is crucial for regulating the endocrine system. It receives input from various brain regions and responds by sending signals that trigger the release of hormones, which either stimulate or suppress the pituitary gland. This gland manages the function of many other glands, such as the thyroid, adrenal glands, and reproductive organs. Additionally, the hypothalamus is involved in managing growth, fluid balance, and milk production. It also plays a key part in regulating body temperature, managing the autonomic nervous system, and controlling hunger and appetite.³

Disruption of hypothalamic activity in KLS may contribute to hypersomnia and behavioural symptoms by interfering with the autonomic nervous system, the neuroendocrine system, and the limbic system.⁴

Endocrine system involvement in KLS

While KLS rarely shows abnormal pituitary hormone levels on routine tests, the endocrine system remains crucial in symptom expression.⁵ The hypothalamic-pituitary axis (HPA axis) regulates hormones and interacts closely with the central nervous system.⁶ Disruptions in this axis may lead to long-term neuroendocrine, autonomic, and metabolic dysregulation.⁷

As hormones in the human body control many essential things in day-to-day life, such as sleep and are very tightly regulated for function, when disturbed, they can cause or worsen certain conditions. Previous studies have shown that when melatonin rhythms get out of sync, it can throw off our sleep patterns and internal body clock. Melatonin is a hormone responsible for managing an individual’s sleep-wake cycle. The studies show that the production of the melatonin hormone with age affects sleep quality and creates sleep disorders. 

Other hormones, such as ghrelin, are also incredibly important to note.⁸ Ghrelin is the most potent growth hormone. Its functions include gastrointestinal motility, gastric acid secretion, and various cardiovascular, immunological, reproductive, and behavioural processes. It is present in the endocrine cells lining the inside of the stomach and in the small intestine and serves as the body’s largest source of ghrelin, which tends to circulate in the blood.⁹ The disruption of ghrelin leads to hyperphagia, which is the sensation of insatiable hunger that often leads to excessive eating.¹⁰

Other hormonal disruptions may also contribute to emotional instability, hallucinations, or hypersexuality observed in patients.

Diagnostic implications and biomarker research 

Diagnosis of KLS is primarily clinical and relies on observation of recurrent hypersomnia with cognitive or behavioural changes. Criteria include:¹¹

• At least two separate episodes of excessive sleep lasting 2 days to 5 weeks
• Episodes occurring multiple times annually or at least once within 18 months
• Normal functioning between episodes
• During episodes, at least one symptom such as cognitive disturbance, perceptual changes, altered eating habits, or unusual behaviour
• Symptoms not explained by other sleep disorders, mental illness, or substance use

No definitive biomarker exists, though ongoing research examines hormonal patterns and neuroimaging as potential diagnostic tools.

Treatment perspectives 

Currently, no cure exists for KLS. Treatment is symptomatic and tailored to individual patients:¹¹

• Stimulants (modafinil, methylphenidate, amphetamines) for excessive sleepiness
• Mood stabilisers (lithium) to reduce episode frequency and severity
• Anti-seizure medications (valproic acid, carbamazepine)
• Antidepressants (fluoxetine, MAOIs)
• Antipsychotics (risperidone, haloperidol)
• Other options: antivirals (acyclovir), melatonin, benzodiazepines, levodopa, and hydrocortisone

Despite these approaches, effectiveness varies due to the rarity and complexity of the disorder.¹²

FAQs

What is KLS?

A rare neurological disorder causing recurrent episodes of extreme sleepiness and behavioural changes, mainly in teenagers.

What triggers KLS episodes?

Often viral infections, stress, or hormonal changes.

Is there a cure for KLS?

No, but medications like stimulants, mood stabilisers, and antidepressants can help manage symptoms.

Does KLS affect normal life between episodes?

No, individuals usually return to normal behaviour and function between episodes.

Can KLS affect females, too?

Yes, but it is more common in adolescent males.

What hormones are involved in KLS?

Melatonin (sleep), ghrelin (hunger), and possibly others are related to the hypothalamus and endocrine system.

Summary

KLS is a rare neurological disorder, mostly seen in teenagers, marked by repeated episodes of excessive sleep (up to 20 hours a day), fatigue, confusion, irritability, overeating, and sometimes hypersexuality. These episodes may last days to weeks, triggered often by viral infections, with symptom-free periods in between. Though its exact cause is unknown, KLS is linked to hormonal imbalances and dysfunction in the hypothalamus, which regulates sleep, hunger, and hormones. Disruptions in hormones like melatonin (sleep) and ghrelin (hunger) can also explain the symptoms.

Diagnosis is based on symptoms and by excluding other conditions. There is no cure, but medications like stimulants, mood stabilisers, and antidepressants may help. Treatment remains experimental due to the condition’s rarity.