What Is Hartnup Disease?

  • Mariam Al-Amari Master's degree, Model-based drug development, The University of Manchester, UK


Hartnup disease is a rare genetic disorder that affects the body's ability to absorb certain nutrients from the diet. While relatively uncommon, this condition helps us understand the complicated aspects of genetics and the importance of early diagnosis and management of rare disorders. This article will delve into the various aspects of Hartnup disease, from its underlying genetic causes to its impact on patients and families, and even the ongoing research aimed at better understanding and treating this condition.


Definition of genetic disorders

Genetic disorders are a diverse group of medical conditions that result from alterations or abnormalities in an individual's genetic material. These disorders are primarily caused by mutations(changes)  in one or more genes or by structural abnormalities in the chromosomes, which are the cellular structures that house the genetic information. Genetic disorders can manifest in different ways, ranging from conditions with mild, moderate, or severe clinical consequences.

The genetic mutations responsible for these disorders can occur spontaneously during the individual's development(de novo mutations), or they can be inherited from one or both parents. The mode of inheritance can follow various patterns, including autosomal recessive, autosomal dominant, X-linked recessive, and X-linked dominant, depending on the specific genetic mutation and the affected gene.

These disorders are characterised by their hereditary nature, meaning they have the potential to be passed down from one generation to the next, often following established Mendelian inheritance patterns. However, some genetic disorders can also arise because of random genetic changes in one person, even if no one else in the family has had the same issue before. 

The presentation, symptoms and clinical manifestations of genetic disorders are incredibly diverse. This is mirrored by known genetic diseases, which include relatively common disorders, like cystic fibrosis and sickle cell anaemia, and rarer conditions, like Hutchinson-Gilford progeria syndrome. Genetic disorders can affect virtually any organ system or bodily function, and the severity of the disorder can vary widely.

Understanding genetic disorders is of paramount importance in the field of medicine and genetics as it allows for early diagnosis, effective management, and sometimes the potential for preventive measures through genetic counselling and testing. Advances in genetic research, such as the mapping of the human genome and the development of advanced sequencing technologies, have significantly improved our ability to identify and characterize genetic disorders, paving the way for more precise diagnostics and targeted treatments. Overall, genetic disorders are a complex area within medical genetics. Ongoing research is focused on understanding the genetic causes and finding ways to improve the lives of those affected.1

Hartnup disease is a rare genetic disorder

Hartnup disease is an example of a rare genetic disorder that has several distinct characteristics. This disorder, first recognised in the early 20th century, primarily arises from mutations in the SLC6A19 gene. This gene encodes a crucial protein responsible for facilitating the absorption of amino acids, particularly tryptophan, in the small intestine and kidneys.

Individuals affected by Hartnup disease exhibit an autosomal recessive inheritance pattern, implying that they inherit two copies of the mutated gene, one from each parent. This genetic configuration makes it difficult to efficiently absorb essential amino acids, leading to various symptoms associated with amino acid deficiencies.2

Clinical presentations of Hartnup disease are notably diverse, encompassing symptoms such as skin rashes, gastrointestinal disturbances, and neurological issues. These symptoms can manifest with varying severity and combinations, making diagnosis and management intricate. Skin rashes, often one of the initial signs, may present as red, scaly, and occasionally pruritic lesions. Gastrointestinal symptoms can include diarrhoea, abdominal pain, and vomiting, while neurological manifestations can include mood disorders, ataxia, and even hallucinations.

Diagnosing Hartnup disease relies on a combination of genetic testing and laboratory assessments, such as urine and blood tests, to detect characteristic amino acid imbalances. Nonetheless, interpreting these results can pose challenges due to individual variability in amino acid levels.

Effective management of Hartnup disease involves dietary adjustments, including a high-protein diet, which aids in compensating for impaired amino acid absorption. Nutrient supplementation, particularly of niacin and tryptophan, may also be necessary to prevent deficiencies. Additionally, medications can help manage specific symptoms, such as topical creams for skin rashes or psychiatric medications for mood disturbances.

Understanding Hartnup disease is pivotal, not only for early diagnosis and management but also for its broader implications in the realm of rare genetic disorders. Research continues to uncover the intricacies of this condition, offering hope for improved diagnostic accuracy and targeted treatments, ultimately enhancing the quality of life for individuals grappling with this rare genetic disorder3

Historical context: Discovery and naming of the disease

The historical context and naming of Hartnup disease provide insights into the origins of our understanding of this rare genetic disorder. Hartnup disease, first identified and described by Sir Archibald Garrod in the early 20th century, represents a crucial milestone in the field of medical genetics. At the time of its discovery, Garrod was pioneering the study of inborn errors of metabolism and the role of genetics in human disease, laying the foundation for the field of biochemical genetics.

The name "Hartnup disease" owes its origin to the Hartnup family, in which the condition was initially identified. In the early 1950s, Garrod conducted extensive research on the family and discovered that several members exhibited a distinctive set of symptoms, including skin rashes, neurological issues, and digestive disturbances. These common symptoms among family members suggested a genetic basis for the disorder.

It was this careful study of the Hartnup family that led to the naming of the condition. By systematically analysing the family's medical history and symptoms, Garrod made the groundbreaking connection between genetics and the observed clinical manifestations. This recognition marked a significant advancement in our understanding of genetic disorders, emphasising the role of heredity in shaping an individual's health.

The naming of Hartnup disease not only honoured the family who played a pivotal role in its discovery but also highlighted the importance of acknowledging the patients and families who serve as crucial participants in the scientific process. This historical context underscores the significance of meticulous observation, systematic investigation, and collaboration between clinicians and researchers in unravelling the mysteries of rare genetic disorders.

Over the years, Hartnup disease has continued to be a subject of study and research, contributing to our broader understanding of genetic disorders and metabolic pathways. Its historical naming serves as a reminder of the foundational work that has paved the way for advancements in genetics and the care of individuals with rare genetic conditions, illustrating how the naming of a disorder can encapsulate a rich history of scientific discovery and collaboration.4

Causes and genetics of hartnup disease

Hartnup disease is primarily attributed to mutations in the SLC6A19 gene, which encodes the B0AT1 protein. This protein plays a pivotal role in the absorption of amino acids, especially tryptophan, within the small intestine and kidneys. When mutations affect the SLC6A19 gene, the B0AT1 protein's function is disrupted, leading to impaired tryptophan absorption and a cascade of symptoms associated with amino acid deficiencies.

The genetics of Hartnup disease follow an autosomal recessive inheritance pattern, as elucidated in scientific research. This means that for an individual to have the disorder, they must inherit two copies of the mutated gene, one from each parent. Importantly, carriers of a single mutated gene (heterozygotes) typically do not display symptoms, as one functional copy of the gene is sufficient for normal tryptophan absorption. However, carriers can potentially pass the mutated gene to their offspring, increasing the risk of the disorder in the next generation. Genetic counselling is thus vital for families with a history of Hartnup disease, as it enables informed reproductive decisions and risk assessment.

The precise genetic mechanisms underlying Hartnup disease have been thoroughly investigated, and advances in molecular genetics have allowed for the identification of specific mutations associated with the disorder. The knowledge of these genetic variations has improved diagnostic accuracy and the understanding of the disease's pathophysiology5.

Symptoms and clinical presentation

Symptoms of Hartnupdisease often include skin rashes, typically presenting as red, scaly, and sometimes itchy lesions. Gastrointestinal symptoms include diarrhoea, abdominal pain, and vomiting. Neurological issues can vary in severity and may involve mood disturbances, ataxia (loss of muscle control), and even hallucinations. It is important to note that the severity and combination of these symptoms can vary among affected individuals, making the clinical presentation of Hartnup disease quite diverse. Early recognition of these symptoms is critical for timely diagnosis and effective management of this rare genetic disorder6.


Methods for diagnosing hartnup disease

Diagnosing Hartnup disease relies on a combination of clinical evaluation, genetic testing, and laboratory assessments. Given its rarity and variability in symptom presentation, a comprehensive diagnostic approach is essential for accurate identification of affected individuals.

Clinical Evaluation: A thorough clinical evaluation is the initial step in diagnosing Hartnup disease. Physicians consider the patient's medical history, including a family history of the disorder, and perform a physical examination to assess the presence of common symptoms such as skin rashes, gastrointestinal issues, or neurological abnormalities. Early recognition of these symptoms is vital for prompt diagnosis.

Genetic Testing: Genetic testing plays a pivotal role in confirming the diagnosis of Hartnup disease. This involves DNA analysis to identify mutations in the SLC6A19 gene, which is responsible for encoding the B0AT1 protein critical for amino acid absorption. Genetic testing provides definitive evidence of the genetic basis of the disorder and is considered a gold standard for diagnosis.7

Laboratory Tests: Laboratory assessments, including urine and blood tests, are conducted to detect characteristic amino acid imbalances associated with Hartnup disease. These tests can reveal decreased levels of tryptophan and other essential amino acids, as well as elevated levels of non-absorbed amino acids in urine samples. While these tests are informative, they may not always provide a conclusive diagnosis, given that amino acid levels can fluctuate and vary among individuals.8

Challenges and potential pitfalls in diagnosis

Nevertheless, diagnosing Hartnup disease presents several challenges and potential pitfalls. These obstacles stem from the disorder's rarity, variability in symptom presentation, and the complexity of diagnostic methods involved.9

  1. Symptom Variability: One of the primary challenges in diagnosing Hartnup disease lies in the broad spectrum of symptoms and their variability among affected individuals. While skin rashes, gastrointestinal issues, and neurological problems are common manifestations, the combination and severity of these symptoms can differ significantly from one person to another. This variability can make it challenging for clinicians to recognise the disorder, especially when symptoms are subtle or mimic other more common conditions.10
  2. Lack of Awareness: Due to its rarity, Hartnup disease may not be on the radar of many healthcare professionals. This lack of awareness can lead to delayed diagnosis or misdiagnosis, potentially causing patients to suffer from unmanaged symptoms or undergo unnecessary medical procedures.
  3. Diagnostic Mimicry: Some of the symptoms of Hartnup disease, particularly skin rashes and gastrointestinal disturbances, can resemble those of other more common dermatological and gastrointestinal conditions. Clinicians may mistake these symptoms for unrelated disorders, resulting in a delayed or inaccurate diagnosis. Healthcare providers need to consider Hartnup disease in the differential diagnosis of patients with unexplained or atypical symptoms.
  4. Genetic Testing Accessibility: While genetic testing is a crucial tool for confirming Hartnup disease, its availability and affordability can be inconsistent, depending on the healthcare system and region. This can lead to delays in obtaining a definitive diagnosis and appropriate management.
  5. Overreliance on Laboratory Tests: Laboratory tests, such as urine and blood amino acid profiles, are informative but not always conclusive. Amino acid levels can fluctuate, and laboratory results may not always reflect the full clinical picture. Relying solely on these tests without considering the broader clinical context can lead to diagnostic pitfalls.2

Treatment and management

Dietary interventions

Dietary interventions play a pivotal role in the treatment and management of Hartnup disease. Given that Hartnup disease primarily affects the absorption of amino acids, particularly tryptophan, from the diet, dietary modifications are essential to compensate for these deficiencies and alleviate associated symptoms.

High-Protein Diet: A cornerstone of dietary management for Hartnup disease is the implementation of a high-protein diet. This approach aims to provide an increased supply of amino acids, including tryptophan, to compensate for the reduced absorption efficiency in the small intestine. A high-protein diet helps address the underlying amino acid imbalances and can significantly improve the patient's overall health and well-being.

Supplementation of Nutrients: In addition to dietary adjustments, nutrient supplementation may be necessary to prevent specific amino acid or vitamin deficiencies. Tryptophan supplementation, in particular, is often prescribed to ensure adequate levels of this essential amino acid. Additionally, niacin (vitamin B3) supplementation is essential since tryptophan is a precursor for niacin synthesis in the body.

Balanced Nutrition: Achieving a balanced nutritional intake is essential for individuals with Hartnup disease to ensure overall health and well-being. Nutrient-rich foods should be included in the diet to provide essential vitamins, minerals, and other amino acids necessary for various bodily functions. A registered dietitian can assist in creating a tailored dietary plan to meet individual nutritional needs.

Hydration: Proper hydration is crucial for individuals with Hartnup disease, as they may experience gastrointestinal symptoms such as diarrhoea and vomiting. Maintaining adequate fluid intake is essential to prevent dehydration and support overall health.

Dietary interventions in Hartnup disease are typically the first line of treatment and can lead to a significant improvement in symptoms and quality of life.11

Medications and their role in managing symptoms

Medications are not typically the primary approach for treating and managing Hartnup disease. However, there are circumstances where medications may be considered adjunctive treatments to address specific symptoms associated with the disorder.

Topical Treatments for Skin Rashes: In some cases, individuals with Hartnup disease may experience skin rashes as a symptom. These rashes can be managed with topical treatments such as emollients and corticosteroid creams to alleviate discomfort and reduce skin inflammation. These medications aim to provide symptomatic relief rather than addressing the underlying cause of the disorder.

Psychiatric Medications: Neurological symptoms, including mood disturbances and psychiatric issues, may be observed in individuals with Hartnup disease. In such cases, psychiatric medications may be prescribed to manage mood disorders and stabilise mental health. However, it's essential to note that these medications target the symptoms rather than the root cause of the disorder.

Pain Management: Some individuals with Hartnup disease may experience abdominal pain or discomfort due to gastrointestinal symptoms. Pain management medications, such as over-the-counter pain relievers or prescribed analgesics, may be used to alleviate abdominal discomfort associated with the disorder.12

Long-term management strategies

Long-term management strategies for Hartnup disease aim to provide affected individuals with a good quality of life by addressing nutritional deficiencies, preventing complications, and minimising the impact of symptoms associated with this rare genetic disorder. These strategies typically encompass ongoing dietary modifications, regular medical monitoring, and supportive care. Here are key aspects of long-term management for Hartnup disease:

Dietary Modifications: The cornerstone of long-term management for Hartnup disease is maintaining a carefully tailored diet. Individuals are encouraged to adhere to a high-protein diet that is rich in tryptophan-containing foods. This dietary approach helps compensate for the impaired absorption of amino acids, particularly tryptophan, in the small intestine. Nutrient-rich foods and appropriate supplementation of vitamins and minerals are also essential to prevent deficiencies and promote overall health.

Regular Medical Monitoring: Regular medical follow-up is crucial to monitor the patient's overall health and nutritional status. Routine blood and urine tests are conducted to assess amino acid levels and identify any deficiencies or imbalances. These assessments guide adjustments to the dietary plan and supplement regimen as needed.

Prevention of Complications: Long-term management includes proactive measures to prevent complications related to amino acid deficiencies. For instance, vitamin B3 (niacin) supplementation is essential to avoid pellagra, a condition caused by niacin deficiency. Prompt identification and management of skin rashes, gastrointestinal symptoms, and neurological issues are also part of preventive care.

Supportive Care: Providing emotional and psychological support to individuals with Hartnup disease and their families is crucial. Coping with the chronic nature of the disorder and potential lifestyle adjustments can be challenging. Access to support groups, counselling, and educational resources can help individuals and families navigate the emotional aspects of living with a rare genetic condition.

Genetic Counselling: Genetic counselling plays a significant role in long-term management, particularly for individuals planning to have children. Genetic counsellors can provide information about the risk of passing on the disorder to offspring and assist in making informed reproductive decisions.

Lifestyle Adaptations: Depending on the severity of symptoms and individual needs, lifestyle adaptations may be necessary. For children, educational support can help manage school attendance and academic performance during periods of illness. Additionally, individuals with Hartnup disease may need to plan their daily activities, including meal planning and dietary adherence, to minimise the impact of the disorder on their lives.11

Research and future directions

Scientists are aiming to delve deeper into various critical aspects of Hartnup disease, with an emphasis on advancing diagnostic capabilities, exploring novel therapeutic approaches, and further exploring the molecular characteristics of the condition.

Researchers are expected to continue investigating the genetic mechanisms that underlie Hartnup's disease. Detailed studies of the SLC6A19 gene and its mutational spectrum will help identify new mutations associated with the disorder. This knowledge can contribute to more comprehensive genetic testing, improving diagnostic accuracy.

Additionally, future research will likely focus on refining diagnostic methods for Hartnup disease. The development of more sensitive and specific genetic tests will aid in the early and precise identification of affected individuals. Advanced molecular techniques, such as next-generation sequencing, may enhance our ability to detect mutations in the SLC6A19 gene.

Investigational research may also explore potential pharmacological interventions to target the molecular pathways disrupted by Hartnup disease. Developing drugs that enhance amino acid absorption or utilisation could offer novel treatment options beyond dietary modifications.

Future studies are also likely to refine nutritional guidelines tailored to individuals with Hartnup disease. These guidelines can provide more specific recommendations on dietary composition, nutrient supplementation, and meal planning to optimise amino acid intake and overall health.

Moreover, research will continue to investigate the long-term outcomes and potential complications associated with Hartnup disease. Understanding the natural history of the disorder and monitoring the health of affected individuals over time will inform strategies for preventing and managing complications


This article on Hartnup disease has highlighted its genetic basis, clinical manifestations, diagnostic challenges, and management strategies. It has also emphasised the importance of early symptom recognition, supportive care, and ongoing research.

Rare genetic disorders like Hartnup disease may not receive widespread attention, but their impact on affected individuals and families is profound. Raising awareness about these conditions is essential to ensure that those affected receive proper care and support.

Continued research and support hold the promise of better outcomes for individuals with Hartnup disease. Through increased awareness, enhanced diagnostic tools, and evolving treatments, we can strive to improve the lives of those living with this rare genetic disorder and pave the way for similar progress in the field of genetics.


Hartnup disease is a rare genetic disorder that affects how the body absorbs important nutrients from food. This condition is a prime example of the intricate world of genetics and the significance of early diagnosis and management for rare disorders. This article explored various aspects of Hartnup disease, from its genetic causes to its impact on patients and families and ongoing research aimed at understanding and treating it.

Genetic disorders are diverse conditions caused by changes in an individual's genes or chromosomes. These alterations can result in a wide range of medical conditions, from mild to severe. Genetic disorders can be inherited from parents or arise spontaneously. Understanding these disorders is essential for early diagnosis, effective management, and sometimes prevention through genetic counselling and testing.

Hartnup disease is a rare genetic disorder caused by mutations in the SLC6A19 gene. This gene normally helps the body absorb amino acids, particularly tryptophan, from the diet. When this gene is mutated, it leads to difficulties in absorbing these essential nutrients, causing a variety of symptoms.

Hartnup disease was first identified and named after the Hartnup family, in which several members displayed common symptoms. This discovery, by Sir Archibald Garrod in the early 20th century, marked a significant advancement in understanding genetic disorders. It highlighted the connection between genetics and clinical symptoms, paving the way for further research in the field of biochemical genetics.

Hartnup disease is primarily caused by mutations in the SLC6A19 gene, which disrupts the absorption of amino acids, especially tryptophan, in the intestine and kidneys. This disorder follows an autosomal recessive inheritance pattern, meaning affected individuals inherit two copies of the mutated gene, one from each parent.

The symptoms of Hartnup disease can vary widely among affected individuals. Common symptoms include skin rashes, gastrointestinal problems like diarrhoea, abdominal pain, and vomiting, as well as neurological issues such as mood disorders, ataxia, and hallucinations. Early recognition of these symptoms is crucial for timely diagnosis.

Diagnosing Hartnup disease involves clinical evaluation, genetic testing, and laboratory assessments. Genetic testing identifies mutations in the SLC6A19 gene, while laboratory tests look for characteristic amino acid imbalances. However, interpreting these results can be challenging due to variations in amino acid levels among individuals.

Diagnosing Hartnup disease can be difficult due to its rarity and variable symptom presentation. Lack of awareness among healthcare providers and similarities with other conditions can lead to misdiagnosis or delayed diagnosis.

Dietary interventions form the foundation of Hartnup disease management. A high-protein diet helps compensate for amino acid absorption issues, and nutrient supplementation may be necessary to prevent deficiencies. Medications are sometimes used to manage specific symptoms.

Long-term management involves maintaining a tailored diet, regular medical monitoring, preventing complications, offering supportive care, and genetic counselling for family planning.

Ongoing research focuses on understanding the genetic mechanisms, improving diagnostics, and exploring potential pharmacological interventions. Researchers are also refining nutritional guidelines and investigating long-term outcomes and complications.

In conclusion, Hartnup disease sheds light on the world of rare genetic disorders. Awareness, early diagnosis, and ongoing research hold promise for improving the lives of those affected by this condition and others like it.


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  2. Kraut JA, Sachs G. Hartnup disorder: unraveling the mystery. Trends Pharmacol Sci. 2005 Feb;26(2):53–5.
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  6. Patel AB, Prabhu AS. Hartnup disease. Indian J Dermatol [Internet]. 2008 [cited 2023 Aug 15];53(1):31–2. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2784584/
  7. Haijes HA, Prinsen HCMT, de Sain-van der Velden MGM, Verhoeven-Duif NM, van Hasselt PM, Jans JJM. Accurate discrimination of Hartnup disorder from other aminoacidurias using a diagnostic ratio. Mol Genet Metab Rep [Internet]. 2019 Dec 27 [cited 2023 Aug 15];22:100551. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6938934/
  8. Wang X, Li XY, Piao Y, Yuan G, Lin Y, Chen H, et al. Hartnup disease presents as hereditary spastic paraplegia and severe peripheral neuropathy. Am J Med Genet A. 2022 Jan;188(1):237–42.
  9. Hartnup disease: practice essentials, background, pathophysiology. 2021 Nov 12 [cited 2023 Aug 15]; Available from: https://emedicine.medscape.com/article/1115549-overview?form=fpf
  10. Orbak Z, Ertekin V, Selimoglu A, Yilmaz N, Tan H, Konak M. Hartnup disease masked by kwashiorkor. J Health Popul Nutr [Internet]. 2010 Aug [cited 2023 Aug 15];28(4):413–5. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2965334/
  11. Ohura T. [Hartnup disorder: Pathogenesis, pathophysiology, and therapy]. Nihon Rinsho. 2006 Feb;64 Suppl 2:541–4.
  12. Hartnup disease treatment & management: medical care, consultations, diet. 2021 Nov 12 [cited 2023 Aug 15]; Available from: https://emedicine.medscape.com/article/1115549-treatment?form=fpf
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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