All of our organs are made up of billions of cells that carry out highly specialised physiological functions to keep us alive. As you can imagine, that is a very demanding job, and in order for the cell to carry out these functions, it needs a constant and reliable energy supply. That’s where the mitochondria come in, the ‘powerhouse’ of cells. The tiny rod-like structures convert nutrients into energy in the form of adenosine triphosphate (ATP), the cellular fuel needed to do their assigned jobs.

But what do you think would happen if this cell-powering structure were to malfunction? The results can be widespread organ and tissue failure, especially in parts of the body that need a lot of energy, such as the muscles, brain, eyes, and ears. An example of a mitochondrial disorder is Kearns-Sayre syndrome (KSS).¹

Brief overview of kearns-sayre syndrome (KSS):

KSS is a rare genetic condition affecting multiple systems in the body due to mutations (changes) in mitochondrial DNA that affect the mitochondria’s ability to produce ATP efficiently. Sensorineural hearing loss is caused by a defect in ATP production, which I will further explore in greater detail in the rest of the article. 

According to the National Organisation for Rare Disorders,² KSS is present in 1 to 3 people out of every 100,000. It is considered rare; as such, many of the materials available online are rendered with convoluted scientific jargon that might limit their accessibility to the wider public. This article aims to bridge that gap by presenting the information in an easy-to-read format. It highlights how and why hearing loss happens in the case of KSS, and how it can be managed.

Understanding kearns-sayre syndrome 

KSS is part of a group of rare genetic disorders that are known as mitochondrial encephalomyopathies because of the lack of energy in high-energy-demanding organs like the brain and muscles.²

Common symptoms

KSS  is characterised by the following:

• Early onset of symptoms that appear before 20 
• Progressive weakness of eye muscles (chronic progressive external ophthalmoplegia) resulting in ptosis (droopy eyelids) and limited eye movement. 
• Retinal degeneration with a distinctive “salt and pepper” appearance (pigmentary retinopathy), leading to vision problems.
• Bilateral and progressive hearing loss 
• Reduced muscle tone, muscle dysmorphia and abnormal appearance of muscle fibres on biopsy
• Neurological defects like ataxia (loss of balance and coordination), tremors, cognitive impairment and maybe even dementia 
• Short stature due to endocrine dysregulation
• Hormonal imbalances and metabolic complications 
• Chronic kidney disease 
• Heart block  (Cardiomyopathy)

Causes

KSS typically results from spontaneous large-scale deletions in mitochondrial DNA (mtDNA). Unlike nuclear DNA (found inside the nucleus), mitochondria have their own DNA. This mtDNA is inherited maternally, as egg cells contribute most of the mitochondria during fertilisation, it is said that we can only inherit mitochondrial disorders from mothers rather than fathers.⁶

How hearing works and hearing loss in KSS

Structure of the ear

Knowing the structure of the ear is essential to comprehending how conditions like KSS affect our hearing. The ear is divided into three regions, the outer, middle and inner ear regions.⁶

• The outer ear, which includes the pinna (auricle) and the auditory canal, captures the sound waves and passes them through to the rest of the ear
• The middle ear, which consists of the tympanic membrane (eardrum) and the ossicles, which are a bony structure made up of the malleus, incus and stapes. It transmits and amplifies sound vibrations from the eardrum to the inner ear via the oval window
• The inner ear, also known as the labyrinth, contains two main units: The cochlear, the main hearing sensory structure the vestibular system, responsible for balance is composed of the vestibule canals and the otolith organs that regulate balance and eye movements

Role of the cochlea and how hearing is affected in KSS

The cochlea is a spiral-shaped fluid structure that resembles the shell of a snail. It produces electrical signals from sound waves. Inside the cochlea are specialised sensory receptors called hair cells that mechanically open ion channels by sound waves, which then leads to depolarisation and the generation of an action potential. This signal is transmitted via the vestibular cochlear nerve to the brain.⁵

When large-scale deletions of mtDNA occur, they impair the function of energy-demanding cells like cochlear hair cells. This causes bilateral sensorineural hearing loss, a hearing loss that affects both ears. Symptoms typically appear in adolescence or early adulthood and may go unnoticed until they interfere with communication.

Symptoms of sensorineural hearing loss in KSS

• Difficulty hearing high-pitched sounds
• Trouble understanding speech, especially in noisy environments 
• Tinnitus
• Gradual progressive hearing loss in both ears

Diagnosing hearing loss in KSS 

The type of hearing loss present in patients with KSS is usually bilateral hearing loss, affecting both ears gradually. The symptoms appear before the age of 20, and the diagnostic process involves a series of specialised tests that include an EEG to detect any heart defects, such as heart blocks and a muscle biopsy to determine if there are any abnormalities in muscle tissues. To assess sensorineural hearing loss, a physical exam is carried out by your audiologist to determine visible issues with the ear. Audigrams are also used to measure hearing sensitivity across frequencies.⁵

Management and support strategies

There is currently no cure for KSS, but symptoms can be managed effectively with a multidisciplinary approach.^3,4

Treatment options

• Hearing Aids - A device that allows you to pick up on sound waves and helps enhance hearing
• Cochlear Implants - In severe cases, they allow direct stimulation of the auditory nerve when the hair cells are not working as they should
• Medication - These are like steroids used to reduce inflammation
• Speech and Language Therapy - improves coping mechanisms and communication abilities
• Multidisciplinary Care Approach - Collaboration between neurologists, audiologists, geneticists, and therapists

Emotional and social impact

Hearing loss can lead to emotional challenges such as frustration or isolation, without the proper support system in place. Hearing devices can restore communication and allow you to independently navigate through everyday life. Educating loved ones on your hearing needs also fosters an environment for understanding and heightened support.

Summary

• Kearns-Sayre syndrome (KSS) is a rare mitochondrial disorder caused by mutations in mitochondrial DNA, leading to widespread organ dysfunction
• Symptoms show up in children and those into their early adulthood, usually in their 20s
• Hearing loss caused by KSS usually occurs gradually and is noticed in both ears, which can be managed through hearing aids, cochlear implants, and supportive therapies.
• Early diagnosis and care approaches are essential for improving the quality of life
• Dealing with KSS requires a strong support and care system for both the individual with illness and family carers