Introduction

Lesch-Nyhan Syndrome (LNS) is a rare metabolic disorder inherited in an X-linked recessive manner. It is most commonly noticed in people assigned male at birth (AMAB) due to the presence of only one X chromosome in their chromosomal formula. Because people assigned female at birth (AFAB) have a chromosomal constitution of two X chromosomes, they are less likely to be affected compared to people AMAB.^1,2 

It is caused by a mutation in the HPRT1 gene, resulting in a deficiency of the hypoxanthine-guanine phosphoribosyltransferase 1 (HPRT). It involves the overproduction of uric acid and marked neurobehavioral abnormalities.³

This syndrome causes brain and behavioural problems, which are not usually observed at birth; however, signs may appear within the first year of life. These may include delays in the acquisition of developmental milestones such as sitting, crawling and walking. Other signs may include low muscle tone (hypotonia), which can progress into dystonia, and lastly, behavioural symptoms, including self-injurious behaviour.⁴  

It is important to understand the neurodevelopmental results of this syndrome, as it can present physical symptoms such as self-mutilation and gout. It is crucial to prevent this because these issues can be a danger to the individual, and by recognising the symptoms, early diagnosis, adequate care, and management can be provided.² 

Pathophysiology and genetics of LNS 

Lesch-Nyhan Syndrome (LNS) is caused by a mutation in the HPRT1 gene, located on the X chromosome at Xq26–q27. This gene encodes the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT), which is essential for the maintenance of nucleotides in the cells. Due to its X-linked recessive inheritance pattern, LNS almost exclusively affects people AMAB; people AFAB are typically asymptomatic carriers, though rare symptomatic cases have been reported due to skewed X-inactivation.⁵

Furthermore, individuals have a lack of HPRT enzyme, which can damage or disrupt the purine salvage pathway. As a result, there will be an overproduction of uric acid (hyperuricemia). This, therefore, can lead to complications such as gout, kidney stones, and uric acid crystals being deposited in the joints and tissues. However, the neurological and behavioural manifestations of the disorder are not directly caused by uric acid buildup.⁶

Neurological manifestations of LNS can be due to the dysfunction in the basal ganglia, specifically the striatum, which is responsible for motor control, behaviour regulations and more. This can be due to a decrease in dopamine in the striatum by around 60-80% which has been observed in patients. Furthermore, tyrosine hydroxylase (TH) activity also decreases.⁷ 

Additionally, alongside basal ganglia dysfunction, individuals may present neurochemical imbalances. Behavioural symptoms may include an alteration in their processing of rewards. Cognitive deficits may include intellectual disability. This can be problematic towards the child as they grow up; they may be slower than their peers, and this can lead to feelings of isolation.⁸ 

Developmental delays in LNS

Motor development can be delayed. Infants typically present with hypotonia in the first few months after birth and will progress further into spasticity. This is most commonly noticed in the lower limbs, which leads to a slow milestone achievement in sitting, crawling and walking. This can result in further complications if individuals present with dystonia or choreoathetosis.⁹ 

Speech and language development can cause impairment in LNS, exhibiting dysarthria. As a result, individuals may struggle with expressive and receptive language. Therefore, communication with others may be difficult due to speech deficits.¹⁰ 

Therefore, social and adaptive functioning can be affected due to difficulty in forming relationships with their peers. Adaptive skills that may be affected may include feeding, dressing and maintaining clean hygiene.¹¹ 

Other developmental delays may include neurodevelopmental problems, particularly between the ages of 3-6 months of age. An issue is that the motor abnormalities can lead to a misinterpretation of the syndrome, as they resemble cerebral palsy or isolated motor disorders.⁴ 

Cognitive impairment in LNS

Cognitive impairment can result in intellectual disability. This does not align with behavioural severity; however, it can cause behavioural dysregulation due to near-normal IQ. Impairments are seen in deficits in control and cognitive flexibility, and difficulty in planning.⁹ 

As the affected child grows, they can face problems with their memory, attention and visuospatial skills. The motor and speech impairments can be identified for the diagnosis of LNS via cognitive assessments; however, it can be difficult due to the testing methods being traditional, with a low percentage of accuracy. For instance, the Wechsler Intelligence Scales and comprehensive neuropsychological batteries can be used to identify any signs.¹² 

It is important to be able to differentiate LNS from other disorders or conditions that may present similar characteristics and symptoms. This can help to prevent incorrect diagnoses and help with management and treatments in order to ensure the best results for a better standard of living are provided to the individual. Hence, they can make appropriate alterations to their daily life to work with peers better and improve any cognitive deficits. Examples of misdiagnosis can be autism spectrum disorders (ASD) or non-specific intellectual disability (ID) syndromes.¹³

ASD and LNS share similar symptoms, such as poor social reciprocity. This may include stereotyped interests, sensory hypersensitivity, which are usually absent. Other conditions include Parkinson’s disease or Tourette’s syndrome, which can be seen to be similar to LNS due to the characteristics of cognitive inflexibility, poor inhibition and goal-directed behavioural impairments. It is usually shown due to the disruption of prefrontal-striatal circuits.¹⁴

Behavioural and psychiatric comorbidities

A hallmark of LNS is severe self-injurious behaviour. It can be pathognomonic for the disorder, which is problematic as it can manifest into biting, head-banging or eye-poking. The behaviour is not due to pain insensitivity but is typically compelled to harm themselves. This can be a compulsive or neuropsychiatric drive.¹⁵ 

Typically, children present impulsivity or have aggressive outbursts, not only towards peers but also to themselves. This can be unprovoked and emotionally incongruent. Other characteristics include repetition in their behaviour, speech or movement. They can also be insistent in specific routines and need to follow a set of steps. Any disruptions alongside rising feelings of anxiety, and these characteristics can be interpreted as obsessive-compulsive disorder (OCD).¹⁶

Lastly, individuals may also have a burst of behaviour, such as anger or crying, frustrations, intolerance and difficulty in managing most of their emotions. 

Clinical management and interventions 

Early diagnosis and genetic counselling

Is it important for early identification for accurate and early diagnosis and management to occur, this way supportive therapies or preparations towards these complications in behaviour can be controlled and focused on prevention? This allows parents, families and carers to be aware of how to respond and how to manage the specific behaviour of their affected child.¹⁷

Other interventions that can facilitate an early diagnosis include genetic counselling. This would also investigate the family history to look for any X-linked inheritance patterns. Furthermore, diagnostic tools can also help with detecting the HPRT1 gene mutation prenatally, allowing the parents to be aware of the child's condition before birth. Hence, they can be aware of how to help the child as they grow and how to ensure the appropriate treatment.¹⁸

Multidisciplinary care

Other management strategies can be team-based approaches, such as occupational and speech therapy. This allows the affected individuals’ motor function, communication and adaptive skills to improve. Physical therapy can increase their muscle tone and mobility. Furthermore, a doctor specialised in paediatric neurology can monitor the motor and neurological symptoms.¹⁹ 

Pharmacologic treatments

Allopurinol is used to reduce uric acid levels, which can help to prevent complications such as kidney stones and gout. It does not affect neurological or behavioural symptoms. Other medications can be benzodiazepines, which help with anxiety or agitation, antipsychotics (e.g., risperidone) to prevent self-injury or SSRIs, which help with anxiety and obsessive-compulsive symptoms.¹⁶

Behavioral interventions

Applied Behavioural Analysis (ABA) is a technique that can be utilised to reduce maladaptive behaviours and ensure positive alternatives. Another option is self-injurious behaviour (SIB) intervention, which helps to prevent self-harm.^20,21

Educational support

Learning, communication, and speech can be difficult when interacting with same-aged peers. Educational support includes alternative support, accommodations for mobility and communication challenges or behavioural support in the school environment. This will allow the child to not feel isolated, different and prevent any difficult behaviour, such as anger and anxiety, from being displayed.²² 

Future directions and research 

Gaps in the research remain a limitation in understanding the syndrome. Specifically, the limited longitudinal studies in understanding the behaviour and symptoms of the child as they grow. This information could help with predicting outcomes and ensure the development of appropriate interventions. Furthermore, people AFAB and carrier phenotypes are underrepresented in research, which should be important to help better understand the condition.²³ 

Future directions must include improved newborn screening to identify families who may present a higher risk towards their newborn presenting this syndrome. This way, early intervention can be carried out. 

Summary

LNS is a rare, inherited metabolic disorder that is a lifelong condition. It is caused by a mutation in the HPRT1 gene and typically affects people AMAB due to the presence of a single X chromosome in their cells. Providing education and increasing awareness of this syndrome is markedly important for an early diagnosis and efficient disease management. Genetic testing and counselling play a leading role in preparing and helping the families and loved ones of an affected child to better adapt, provide adequate support and meet the specific needs a LNS patient presents.