Overhydrated Hereditary Stomatocytosis: Causes, Symptoms, and Treatment
Medically reviewed by Harsha Moole, MD, Internal Medicine. Last reviewed: October 2, 2026.
What kind of doctor treats Overhydrated Hereditary Stomatocytosis?
A primary care doctor is usually the first stop and can order the first blood tests. Because the condition is rare, care often involves a hematologist, and the two usually work together. A direct primary care or concierge doctor, with longer visits and more time to coordinate care, can be a good partner; when anemia is serious, they would refer to a hematologist and stay involved for follow-up.
What it is
Overhydrated hereditary stomatocytosis is a very rare blood condition present from birth. Stomatocytes are red blood cells with a small mouth-like slit, called a stoma, instead of the normal round dent. In this condition, the cells let in too much water and salt and swell. Swollen cells are fragile and break apart sooner than they should, causing hemolytic anemia, meaning the blood has trouble carrying enough oxygen.
Symptoms
Many people have mild symptoms, and some have none at all. When symptoms appear, they often come from the anemia: tiredness, weakness, paleness, or shortness of breath during activity. The skin or eyes may look yellow (jaundice), the spleen may enlarge, and some people develop gallstones.
Causes and who gets it
This condition is usually caused by a mutation in the RHAG gene, which helps red blood cells control how much water and salt they hold. It is passed down in an autosomal dominant pattern, meaning a child only needs the changed gene from one parent.
How doctors diagnose it
Doctors often start with a complete blood count. Under a microscope, a lab worker can see the mouth-like slit that gives the condition its name. A genetic test can confirm the changed gene, which is usually RHAG. Doctors may also rule out more common causes of anemia first.
Treatment
There is no single cure, and many people need no treatment beyond watching the anemia. Some people need folic acid, and transfusions may be given in severe cases. Doctors usually avoid removing the spleen because it can cause dangerous blood clots. Certain drugs, including some diuretics, can make red blood cells break down faster, so patients should tell every doctor about the diagnosis before starting new medicines.
When to see a doctor
Anyone with lasting tiredness, pale or yellow skin, or fullness in the upper left belly should see a doctor. Sudden severe weakness, chest pain, or trouble breathing needs urgent attention.
Common questions
Is overhydrated hereditary stomatocytosis dangerous?
For many people it is mild, and some never have symptoms. Others develop anemia that needs ongoing care. A doctor can explain what the blood tests mean for a specific person.
Can it be passed to my children?
Yes, it can. Because it follows an autosomal dominant pattern, a parent with the condition has a one in two chance of passing the changed gene to each child.
Can I exercise if I have this condition?
Most people with mild anemia can be active. A doctor may suggest adjusting activity if anemia is more severe, since the body may get less oxygen during exercise.
Why do some medicines cause problems?
In this condition, red blood cells are already swollen and fragile. Certain drugs, including some diuretics, can push more water into the cells and make them break down faster. Always mention the diagnosis before starting a new medicine.
Sources
- NIH Genetic and Rare Diseases Information Center - Overhydrated hereditary stomatocytosis
- MedlinePlus - Anemia
Medical Disclaimer
This content is for general educational and informational purposes only and is not medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment, and reading it does not create a doctor-patient relationship. Always seek the advice of your physician or another qualified health provider with any questions about a medical condition, and never disregard or delay seeking professional advice because of something you read here. If you think you may have a medical emergency, call 911 (or your local emergency number) immediately.
