MNGIE (mitochondrial neurogastrointestinal encephalomyopathy): symptoms, diagnosis and treatment

MNGIE is a form of mitochondrial disease. Mitochondria are structures within cells that generate energy, and the Lily Foundation explains that MNGIE primarily affects the digestive and nervous systems and varies in severity: some people develop quite severe disease early in life, and others do not develop symptoms until much later.

A Health Research Authority (HRA) research summary describes MNGIE as a disease which affects the digestive and nervous systems, leading to nutritional failure and muscular disability, and states that the faulty TYMP gene codes for thymidine phosphorylase, the enzyme responsible for breaking down thymidine and deoxyuridine. These substances accumulate and damage the DNA found in mitochondria, affecting mitochondrial function.

The Lily Foundation puts the same idea in plainer language: the enzyme normally helps the body clear toxic waste products that all cells produce, and when it does not work, those waste products are not cleared and build up over time, damaging particularly the gut and nervous system.

The Lily Foundation says MNGIE affects multiple organs and symptoms vary from person to person. They often begin in childhood but can go unnoticed for many years, and the condition presents predominantly with either disturbances of bowel function or weakness largely due to a damaged nerve supply.

• Gastrointestinal problems: severe digestive problems caused by disruption to normal bowel function.

• Neurological symptoms: weakness and nerve damage from damage to the peripheral nervous system.

• Cognitive difficulties: affecting approximately 10% of those affected.

The Lily Foundation says that some people develop symptoms early in childhood or adolescence, and these cases often progress more quickly and may be more severe earlier on. Others develop symptoms later in adulthood and often have milder symptoms at first, with slower progression. The difference in age of onset and severity is what doctors refer to when they talk about different phenotypes.

This variation is one reason diagnosis can take time. Because the early digestive symptoms overlap with common conditions, it may be some years before a pattern across the gut and nervous system is recognised.

The Lily Foundation says that because symptoms can be similar to other digestive conditions such as Crohn’s disease or coeliac disease, specialist testing is essential to reach a confirmed diagnosis. Diagnosis usually involves a combination of assessment by specialist mitochondrial teams, blood tests to measure thymidine phosphorylase enzyme activity and genetic testing to identify mutations in the TYMP gene.

It notes that genetic counselling is available via NHS services to help those affected understand inheritance patterns and future family planning options.

As with all forms of mitochondrial disease, the Lily Foundation says there is currently no cure for MNGIE and that existing treatments focus on managing symptoms and improving quality of life rather than treating the underlying cause. It describes two potential long-term treatment options that aim to address the underlying cause, bone marrow transplant and liver transplant, both of which aim to introduce healthy cells with normal enzyme activity. It stresses that these treatments are complex, have associated risks and are not suitable for everyone.

The HRA summary of a UK study describes another approach: taking about a cup of the patient’s own blood, loading the functional enzyme into the patient’s red blood cells to form erythrocyte-encapsulated thymidine phosphorylase (EE-TP), and giving it back by infusion, which prolongs the enzyme’s half-life and may minimise immune reactions. The study, sponsored by St George’s University of London, planned to enrol 12 adult and 8 adolescent or paediatric patients. A separate HRA summary reports a blood biomarker, miR-34a-5p, which was elevated in patients and decreased during enzyme replacement therapy in four patients, coinciding with biochemical or clinical improvement.

The Lily Foundation adds that gene therapies, liver transplants and engineered enzyme replacement therapies are being investigated, and are still at the pre-clinical stage, with plans for a global natural history study.

MNGIE is a serious progressive condition. The HRA summary states that it leads to nutritional failure and muscular disability, causing death at around 38 years old in the populations described. This is a population-level statement from a research summary, and because the condition varies widely in severity and onset, and treatment options are changing, individual outlook is best discussed with a specialist mitochondrial team.

The Lily Foundation points to the NHS Highly Specialised Service for Mitochondrial Disorders, based in London, Newcastle and Oxford, which provides expert care including diagnosis, symptom management and disease monitoring.

Diagnosis and long-term care for MNGIE in the UK run through highly specialised NHS mitochondrial services, usually reached by referral from a gastroenterologist, neurologist or paediatrician. Transplant approaches and clinical trials are delivered in specialist centres.

Private care is unlikely to replace these services for such a rare condition, but second opinions and genetic testing are sometimes sought. Results should be shared with the NHS specialist team.