```html

Paroxysmal Nocturnal Hemoglobinuria (PNH) – A Patient‑Friendly Medical Guide

Overview

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life‑threatening blood disorder caused by a mutation in the PHRF1 (formerly PIGA) gene. The mutation leads to a deficiency of surface proteins (CD55 and CD59) that normally protect red blood cells (RBCs) from the immune system’s complement cascade. Without these protective proteins, RBCs are destroyed (intravascular hemolysis), leading to the classic symptom of dark urine, especially in the morning.

PNH can affect anyone, but it most commonly presents in young adults (median age ≈ 35 years) and is slightly more frequent in males than females.

Prevalence: Approximately 1–2 cases per million people worldwide (≈ 5–10 cases per 10 million) 【1】. In the United States, there are an estimated 5,000–6,000 diagnosed individuals.

Symptoms

Symptoms result from three main processes: hemolysis, thrombosis, and bone‑marrow failure. Not every patient experiences all of them.

• Hemolysis‑related
  • Dark (tea‑colored) urine, especially upon waking.
  • Fatigue and weakness due to anemia.
  • Shortness of breath on exertion.
  • Abdominal or chest pain from hemoglobinuria‑induced irritation.
• Thrombosis‑related
  • Sudden, unexplained pain in the leg (deep‑vein thrombosis) or abdomen (hepatic, portal, or cerebral veins).
  • Headache, visual changes, or neurological deficits if cerebral veins are involved.
• Bone‑marrow failure
  • Pancytopenia – low counts of red cells, white cells, and platelets.
  • Frequent infections (low neutrophils).
  • Easy bruising or bleeding (low platelets).
• Other possible manifestations
  • Gallstones (from chronic hemolysis).
  • Kidney dysfunction due to hemoglobin deposition.
  • Iron deficiency anemia secondary to chronic urine loss.

Causes and Risk Factors

Underlying cause

PNH is not inherited. It results from an acquired somatic mutation in the PIGA gene in a hematopoietic stem cell. The mutation disables the synthesis of the glycosylphosphatidylinositol (GPI) anchor, a molecular “tether” that holds CD55 (decay‑accelerating factor) and CD59 (membrane‑inhibitor of reactive lysis) on the cell surface. Without CD55/CD59, complement proteins attack and lyse the cell.

Risk factors

• Age: Median diagnosis at 30‑40 years, but cases range from childhood to late adulthood.
• Existing bone‑marrow failure syndromes: About 30 % of patients have prior aplastic anemia or myelodysplastic syndrome (MDS).
• Environmental exposures: No definitive links, though some case series suggest a possible association with prior chemotherapy or radiation.

Diagnosis

Because symptoms overlap with many other hematologic disorders, a stepwise approach is used.

1. Clinical suspicion

• Unexplained hemolytic anemia + dark urine.
• Thrombosis in atypical sites (e.g., hepatic vein).
• History of aplastic anemia/MDS.

2. Laboratory tests

• Complete blood count (CBC) – reveals anemia, possible leukopenia or thrombocytopenia.
• LDH (lactate dehydrogenase) – markedly elevated in active hemolysis.
• Haptoglobin – low or undetectable.
• Uro‑ and hemoglobinuria – positive dipstick for blood without red cells on microscopy.
• Reticulocyte count – increased as bone marrow compensates.

3. Flow cytometry – the gold‑standard test

Peripheral blood is stained with fluorescent antibodies against GPI‑anchored proteins (CD55, CD59, and others). The proportion of cells lacking these proteins is quantified. A clone size > 5 % on granulocytes or monocytes is diagnostic.

4. Additional assessments

• Bone‑marrow biopsy – evaluates cellularity, especially if pancytopenia is present.
• Imaging – CT or MRI to rule out thrombosis when symptoms suggest.
• Thrombotic risk labs – D‑dimer, fibrinogen, and antiphospholipid antibodies (to exclude other causes).

Treatment Options

Therapy is aimed at three goals: halt complement‑mediated hemolysis, prevent thrombosis, and address bone‑marrow failure.

Complement inhibitors (first‑line)

• Eculizumab (Soliris®) – a monoclonal antibody that binds C5, preventing formation of the membrane‑attack complex. FDA‑approved for PNH in 2007.
• Ravulizumab (Ultomiris®) – a longer‑acting C5 inhibitor; dosing every 8 weeks vs. every 2 weeks for eculizumab.
• Benefits: Reduces hemolysis, diminishes transfusion needs by ~80 %, and lowers thrombotic risk by 70 % 【2】.
• Safety: Increases susceptibility to encapsulated bacteria, especially Neisseria meningitidis. Vaccination (meningococcal ACWY & B) is required ≥2 weeks before first dose; prophylactic antibiotics are sometimes prescribed.

Bone‑marrow directed therapy

• Immunosuppressive therapy (IST) – antithymocyte globulin (ATG) + cyclosporine for patients with concurrent aplastic anemia.
• Hematopoietic stem‑cell transplantation (HSCT) – curative for select young patients with severe marrow failure; high risk of graft‑versus‑host disease.

Supportive care

• Iron supplementation – only after iron studies confirm deficiency; excess iron can accumulate from chronic hemoglobinuria.
• Folic acid – 1 mg daily to support erythropoiesis.
• Red blood cell transfusions – for symptomatic anemia while awaiting definitive therapy.
• Anticoagulation – lifelong warfarin or direct oral anticoagulant (DOAC) is recommended after a thrombotic event; some clinicians use prophylactic anticoagulation in high‑risk clones even without a clot.

Lifestyle & adjunct measures

• Stay well‑hydrated to reduce blood viscosity.
• Avoid smoking and excessive estrogen (e.g., oral contraceptives) which increase clot risk.
• Prompt treatment of infections; maintain up‑to‑date vaccinations.

Living with Paroxysmal Nocturnal Hemoglobinuria

Daily management tips

1. Medication adherence – schedule complement‑inhibitor infusions and never miss a dose; missed doses can trigger rapid hemolysis.
2. Regular laboratory monitoring – CBC, LDH, renal function, and complement levels every 1–3 months.
3. Recognize early signs of thrombosis – new leg swelling, abdominal pain, or neurological symptoms should prompt immediate evaluation.
4. Vaccination upkeep – annual flu shot, COVID‑19 boosters, pneumococcal vaccine, and ensure meningococcal protection.
5. Travel considerations – carry a letter from your hematologist, a copy of your medication schedule, and a supply of antibiotics for emergency use if you develop fever while on complement inhibitors.
6. Psychosocial support – join patient groups (e.g., PNH International Registry) and consider counseling to manage chronic disease stress.

Work & lifestyle

Most patients can maintain employment, but flexible work hours help accommodate infusion appointments. Physical activity is encouraged, but high‑impact sports that increase injury risk should be avoided if platelet counts are low.

Prevention

Because PNH originates from a random genetic mutation, primary prevention is not possible. However, secondary measures can reduce complications:

• Vaccinate against meningococcus before starting complement inhibitors.
• Control modifiable clot risk factors – maintain healthy weight, quit smoking, limit estrogen exposure.
• Promptly treat infections to avoid triggering complement activation.

Complications

If left untreated or poorly controlled, PNH can lead to serious, life‑threatening issues:

• Venous thrombosis – the leading cause of mortality; can affect hepatic, portal, cerebral, or pulmonary veins.
• Severe anemia – may cause high‑output cardiac failure.
• Renal failure – chronic hemoglobin deposition damages tubules.
• Iron overload – from repeated transfusions; leads to organ dysfunction.
• Progression to acute leukemia – especially in patients with underlying MDS.
• Infections – especially meningococcal sepsis in patients on C5 inhibitors.

When to Seek Emergency Care

---

References

1. Mayo Clinic. “Paroxysmal nocturnal hemoglobinuria.” Updated 2023. https://www.mayoclinic.org
2. Hill A, et al. “Eculizumab in paroxysmal nocturnal hemoglobinuria.” New England Journal of Medicine. 2006;355:1233‑1243.
3. NIH National Heart, Lung, and Blood Institute. “PNH Treatment Guidelines.” 2022. https://www.nhlbi.nih.gov
4. World Health Organization. “Guidelines on the management of rare blood disorders.” 2021.
5. Cleveland Clinic. “Paroxysmal Nocturnal Hemoglobinuria (PNH).” 2023. https://my.clevelandclinic.org

```