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McLeod syndrome
This X-linked neurodegenerative disorder mainly affects males, leading to movement difficulties, cognitive changes, and psychiatric symptoms. It also involves abnormalities in red blood cells, impacting various body systems.
Overview
McLeod syndrome is a very rare genetic condition that primarily affects males. It is characterised by a combination of neurological symptoms, psychiatric features, and a specific type of red blood cell abnormality [PMID:33671285]. The condition often progresses slowly, and its effects can vary significantly among individuals.
The syndrome was first identified in 1961 and is named after the first patient diagnosed with the unique blood group characteristics. It is considered part of a broader group of conditions known as neuroacanthocytosis syndromes, which involve both neurological problems and misshapen red blood cells called acanthocytes [PMID:17953265].
Symptoms & clinical features
The symptoms of McLeod syndrome typically begin in middle adulthood, although onset can vary. Early signs often include muscle weakness and wasting, involuntary movements such as tics, and a shuffling gait [PMID:17953265]. Over time, individuals may develop a range of motor difficulties, including dystonia (sustained muscle contractions) and chorea (irregular, unpredictable movements).
Beyond motor symptoms, psychiatric and cognitive changes are common. These can include personality changes, depression, anxiety, obsessive-compulsive behaviours, and sometimes psychosis. Cognitive decline, affecting memory and executive functions, may also occur. Additionally, heart problems like cardiomyopathy (heart muscle disease) and arrhythmias (irregular heartbeats) have been reported in some individuals [PMID:33671285].
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Affected organs
McLeod syndrome primarily affects the brain and nervous system, leading to the characteristic neurological and psychiatric symptoms. Specific areas of the brain, particularly those involved in movement control (like the basal ganglia), can show changes over time. The heart can also be affected, with potential for cardiomyopathy and arrhythmias. The condition also impacts red blood cells, causing them to develop an unusual spiky shape (acanthocytosis), which can lead to chronic, mild anaemia, although this is not always clinically significant.
Risks & severity
The severity of McLeod syndrome can vary widely between affected individuals, even within the same family. Symptoms typically begin in adulthood, often between the ages of 30 and 60, but cases with earlier or later onset are known. The condition is progressive, meaning symptoms tend to worsen over time [PMID:33671285]. Life expectancy can be reduced due to complications such as heart failure or severe neurological impairments. Due to its rarity, exact prevalence figures are not well established, but it is considered a very rare disease.
Genetic causes
McLeod syndrome is caused by pathogenic variants in the *XK* gene. The *XK* gene provides instructions for making the Kx protein, which is found on the surface of red blood cells and other cell types. This protein is essential for the structure and function of red blood cells and is closely associated with the Kell blood group antigen system.
When the *XK* gene has a pathogenic variant, it leads to a lack or dysfunction of the Kx protein. This absence or alteration of the Kx protein is believed to be central to the development of both the neurological features and the red blood cell abnormalities seen in McLeod syndrome [PMID:17953265]. The exact mechanism by which Kx protein deficiency leads to brain degeneration is still an area of ongoing research.
- XK X-linked Kx blood group antigen, Kell and VPS13A binding protein
Inheritance pattern
McLeod syndrome has an X-linked recessive inheritance pattern. This means the *XK* gene is located on the X chromosome. Males have one X and one Y chromosome, so if their single X chromosome carries a pathogenic *XK* variant, they will develop the condition.
Females have two X chromosomes. If one X chromosome carries a pathogenic *XK* variant, they usually do not develop the full syndrome because their other, healthy X chromosome can compensate. However, female carriers may sometimes show milder symptoms, such as an altered blood type (weak Kell antigens) or a slight increase in acanthocytes, and in rare cases, they can develop mild neurological or psychiatric features.
X-linked recessive: sons of a carrier mother have a 50% chance of being affected. Daughters have a 50% chance of being carriers.
Diagnosis & testing
Diagnosis of McLeod syndrome typically involves a combination of clinical assessment, blood tests, and genetic testing. Suspicion often arises from observing the characteristic neurological and psychiatric symptoms along with unexplained red blood cell abnormalities (acanthocytosis). Specific blood tests can detect the absence of Kell blood group antigens, which is a key indicator [PMID:17953265].
Confirmation of McLeod syndrome is made through genetic testing of the *XK* gene to identify a pathogenic variant. In the UK, genetic testing for suspected McLeod syndrome may be accessed via the NHS Genomic Medicine Service (GMS) pathways, often following referral from a neurologist or clinical geneticist. Relevant testing falls under NHS R-codes related to neurodegenerative disorders.
Management & lifestyle
Currently, there is no cure for McLeod syndrome, so management focuses on addressing the symptoms and improving quality of life. This can involve a multidisciplinary team approach, including neurologists, psychiatrists, cardiologists, and physiotherapists.
Medications may be used to help manage specific symptoms like involuntary movements or psychiatric issues. Regular monitoring for cardiac complications is important. Physical therapy, occupational therapy, and speech therapy can help maintain function and independence. Genetic counsellors can provide information and support to affected individuals and their families regarding the inheritance pattern and implications for family planning.
UK care pathway
In the UK, individuals suspected of having a rare genetic condition like McLeod syndrome would typically be referred by their GP or a specialist to a regional Clinical Genetics service. This service can provide expert assessment, genetic counselling, and arrange for appropriate genetic testing through the NHS Genomic Medicine Service (GMS). The GMS utilises a national testing directory, with relevant R-codes for neurogenetic conditions, to guide testing strategies. Genetic counsellors play a vital role in explaining inheritance patterns, testing options, and potential implications for family members.
Frequently asked questions
What is the difference between McLeod syndrome and Huntington's disease?
While both conditions can cause involuntary movements and neurological symptoms, McLeod syndrome is caused by pathogenic variants in the *XK* gene on the X chromosome and also affects red blood cells. Huntington's disease is caused by variants in the *HTT* gene and does not involve the same red blood cell abnormalities or X-linked inheritance pattern.
Can women get McLeod syndrome?
McLeod syndrome primarily affects males due to its X-linked recessive inheritance. Females who carry a pathogenic *XK* variant typically do not develop the full syndrome, but some may experience milder symptoms or specific blood changes, though this is rare.
What kind of tests are used to diagnose McLeod syndrome?
Diagnosis usually involves looking for neurological and psychiatric symptoms, specific blood tests to identify the absence of Kell blood group antigens and the presence of spiky red blood cells (acanthocytes), and confirmation through genetic testing of the *XK* gene.
Is there a cure for McLeod syndrome?
Currently, there is no cure for McLeod syndrome. Treatment focuses on managing symptoms to improve quality of life. This can include medications for movement disorders or psychiatric issues, as well as physical, occupational, and speech therapy.
How does McLeod syndrome affect family planning?
Due to its X-linked inheritance, understanding the genetic status of family members is important for family planning. Genetic counselling can provide detailed information about the risk of passing on the condition and available reproductive options.
References
- Feriante J, Gupta V. Neuroacanthocytosis. 2023. PMID: 32809602
- Walker RH, Jung HH, Danek A. Neuroacanthocytosis. Handbook of clinical neurology. 2011. PMID: 21496574
- Danek A, Walker RH. Neuroacanthocytosis. Current opinion in neurology. 2005. PMID: 16003113
- Jung HH, Danek A, Walker RH. Neuroacanthocytosis syndromes. Orphanet journal of rare diseases. 2011. PMID: 22027213
- Peikert K, Hermann A, Danek A. XK-Associated McLeod Syndrome: Nonhematological Manifestations and Relation to VPS13A Disease. Transfusion medicine and hemotherapy : offizielles Organ der Deutschen Gesellschaft fur Transfusionsmedizin und Immunhamatologie. 2022. PMID: 35221863
- Walker RH. Management of Neuroacanthocytosis Syndromes. Tremor and other hyperkinetic movements (New York, N.Y.). 2015. PMID: 26504667
- Jung HH, Danek A, Frey BM. McLeod syndrome: a neurohaematological disorder. Vox sanguinis. 2007. PMID: 17683354
- Deutschländer AB, Dickson DW, Wszolek ZK. Neuropathology of McLeod Syndrome. Movement disorders : official journal of the Movement Disorder Society. 2022. PMID: 34913196