Doctors discovered that a young boy’s dark urine was caused by a rare genetic condition called Imerslund-Gräsbeck syndrome (IGS). This condition makes it hard for the body to absorb vitamin B12 and causes protein to leak into the urine. The boy had a mutation in a gene called AMN that he inherited from both parents. Even though doctors tried a common kidney medicine, it didn’t help reduce the protein in his urine. After four years, his kidneys stayed healthy and stable. This case helps doctors understand that this rare disease can show up in different ways and may not respond to typical treatments.

The Quick Take

  • What they studied: A single case of a young child with dark urine caused by a rare genetic disorder that affects how the body absorbs vitamin B12 and handles protein
  • Who participated: One 3-year-old boy from a family where the parents were cousins (which increases the chance of rare genetic conditions), and a female cousin also had protein in her urine
  • Key finding: The boy had a genetic mutation in the AMN gene that caused Imerslund-Gräsbeck syndrome, leading to low vitamin B12 levels and protein leaking into his urine. A common kidney medicine didn’t help, but his kidneys stayed stable over 4 years
  • What it means for you: If you or a family member has unexplained protein in urine and low B12 levels, especially with family history of similar problems, genetic testing might be important. This condition is very rare, but knowing about it helps doctors diagnose it correctly

The Research Details

This is a case report, which means doctors documented the medical story of one patient in detail. The 3-year-old boy came to the hospital with dark-colored urine that had been happening for 4 months. Doctors ran blood tests, urine tests, and took a small sample of kidney tissue to look at under a microscope. They also did genetic testing to find out what caused his symptoms. They followed his health for 4 years to see how his condition changed over time.

The doctors checked for common causes of his symptoms first, like infections, but found none. They noticed his vitamin B12 was very low even though he was taking B12 supplements. The kidney biopsy didn’t show typical kidney disease patterns, which made the diagnosis tricky. This is why genetic testing became important to find the real cause.

Case reports are important for rare diseases because they help doctors recognize unusual patterns they might not see otherwise. Since Imerslund-Gräsbeck syndrome is very rare, most doctors have never seen it. By publishing this detailed case, other doctors around the world can learn what to look for and how to diagnose it correctly in their own patients.

This is a single case report, which is the lowest level of research evidence. However, for rare diseases, case reports are valuable because they provide detailed real-world information. The diagnosis was confirmed with genetic testing, which is very reliable. The long-term follow-up of 4 years is a strength because it shows what happens to the patient over time. The main limitation is that we can only learn about one person’s experience, not whether findings apply to others with the same condition.

What the Results Show

The genetic testing confirmed that the boy had two copies of a mutated AMN gene (one from each parent), which caused Imerslund-Gräsbeck syndrome. This genetic mutation prevented his body from properly absorbing vitamin B12 from food, leading to dangerously low B12 levels. The mutation also caused protein, especially a protein called albumin, to leak into his urine, making it dark-colored.

When doctors gave him a common kidney medicine called an ACE inhibitor (used to reduce protein in urine), it didn’t work. His protein levels stayed the same whether he took the medicine or not. This was unusual because this medicine usually helps reduce protein in urine for other kidney conditions.

The good news was that over 4 years of follow-up, his kidney function remained stable and didn’t get worse. His kidneys continued to work normally even though protein was still leaking into his urine. This suggests that this particular type of protein leakage may not damage kidneys the way other types do.

The kidney biopsy showed normal kidney tissue under the microscope, which was surprising given the protein in his urine. This finding helped rule out other kidney diseases. The family history was also important: his parents were cousins (related by blood), which increased the chance of rare genetic conditions. A female cousin also had protein in her urine, suggesting she might carry the same genetic mutation.

Imerslund-Gräsbeck syndrome is usually known for causing a type of anemia (low red blood cells) called megaloblastic anemia, which happens because B12 is needed to make healthy blood cells. However, this case shows that the condition can present differently in different people. Some patients may have more kidney problems than blood problems. This case adds to medical knowledge by showing that the AMN gene mutation can cause variable symptoms depending on the individual.

This is only one patient’s story, so we cannot know if all patients with this genetic mutation will have the same experience. The study doesn’t compare this patient to others with the same condition. We don’t know the long-term outcome beyond 4 years. The case doesn’t explain why some people with this mutation develop kidney problems while others might not. More research with multiple patients would help answer these questions.

The Bottom Line

If you have unexplained protein in urine combined with low vitamin B12 levels, ask your doctor about genetic testing for Imerslund-Gräsbeck syndrome, especially if you have family members with similar problems or if your parents are related by blood. Taking vitamin B12 supplements is important for managing this condition. Standard kidney medicines may not work for the protein in urine, so your doctor may need to monitor your kidneys with regular blood and urine tests instead. (Confidence level: Low to Moderate - based on one case report)

This information is most relevant for: families with a history of unexplained protein in urine and B12 deficiency, people from communities where cousin marriages are more common, and healthcare providers who see patients with unusual combinations of kidney and B12 problems. Most people don’t need to worry about this condition since it’s extremely rare. However, if you have symptoms like dark urine, fatigue, or numbness in your hands and feet combined with low B12, mention this to your doctor.

Imerslund-Gräsbeck syndrome is a lifelong condition that requires ongoing management. Vitamin B12 supplementation needs to continue indefinitely. Kidney function may remain stable for years, as shown in this case, but regular monitoring is important. Changes in kidney function could take months or years to develop, so consistent check-ups are necessary.

Want to Apply This Research?

  • If diagnosed with this condition, track monthly vitamin B12 levels and quarterly urine protein amounts using the app’s lab result logging feature. Set reminders for B12 supplement doses and kidney function check-ups every 3-6 months.
  • Set daily reminders to take vitamin B12 supplements as prescribed. Log any changes in urine color or appearance. Track energy levels and any symptoms of B12 deficiency (fatigue, numbness) to share with your doctor.
  • Create a long-term health dashboard showing trends in B12 levels, protein in urine, and kidney function tests over time. Use the app to schedule and track regular doctor appointments for kidney monitoring. Set alerts if lab values fall outside normal ranges to prompt medical consultation.

This article describes a single rare case and is for educational purposes only. It is not medical advice. Imerslund-Gräsbeck syndrome is extremely rare, and most cases of protein in urine have different causes. If you or your child has dark urine, protein in urine, or low vitamin B12 levels, consult with a qualified healthcare provider for proper evaluation and diagnosis. Do not start, stop, or change any medications based on this information without medical guidance. Genetic testing and specialized care should only be pursued under professional medical supervision.