HE vs. HPP: What's the Difference?

Hereditary Pyropoikilocytosis (HPP, pronounced pie-row-poy-kill-oh-sigh-TOE-sis) is a rare, severe subtype of Hereditary Elliptocytosis (HE). The main difference between the two lies in their genetics: mild HE typically occurs when a person inherits one mutated gene (autosomal dominant inheritance), while HPP happens when a person inherits two related genetic changes (autosomal recessive inheritance) ^[1][2]. This double inheritance in HPP leads to extremely fragile red blood cells and severe anemia that usually begins in infancy, whereas mild HE features intact, oval-shaped cells and often causes no symptoms at all ^[1][3][4].

The Genetic Difference: One Gene vs. Two

To understand HPP, it helps to look at how red blood cell disorders are passed down through families.

Mild Hereditary Elliptocytosis is usually heterozygous, meaning a person has one normal gene and one mutated gene (often involving the SPTA1, SPTB, or EPB41 genes) ^[1][2]. Because they still have one working gene, their red blood cells produce enough structural protein to remain mostly stable.

HPP, however, is a recessive or compound heterozygous condition, meaning the patient inherited a genetic defect from both parents ^[1][3]. Most commonly, this involves inheriting a structural mutation from one parent and a specific low-expression gene variant (known as the alpha-LELY allele) from the other ^[3][5]. On its own, the alpha-LELY variant is harmless. However, when paired with an HE mutation, it drastically reduces the amount of normal structural protein the body can produce, leading to the severe symptoms of HPP ^[3][6].

Physical Differences in the Blood Cells

These genetic differences directly affect the “skeleton” of the red blood cell, changing how the cells look and behave:

• Mild HE: The red blood cells are shaped like ellipses or cigars (elliptocytes) but are strong enough to circulate through the body and survive a normal lifespan ^[1][7].
• HPP: The membrane skeleton is profoundly unstable. Under a microscope, the blood cells look highly fragmented (schistocytes, pronounced shis-toe-sites) and unusually small (microspherocytes) ^[3][8]. A unique hallmark of HPP is thermal sensitivity. Normal red blood cells fragment at very high temperatures (49°C or 120°F), but HPP cells break apart at lower temperatures (45-46°C or 113-114.8°F) ^[3][8].
  • Note on Heat Sensitivity: This is strictly a laboratory test used by pathologists to diagnose the condition. A temperature of 113°F is well above any human body temperature, even during a severe fever. You do not need to worry that summer heat, saunas, hot tubs, or normal childhood fevers will cause your blood cells to break apart.

Symptom Severity: Asymptomatic vs. Severe Anemia

Because HPP cells are so fragile, the clinical experiences of patients are vastly different from those with mild HE:

• Mild HE: The condition is often completely asymptomatic (causing no symptoms). Many people only discover they have it incidentally during routine blood work, and they usually do not require any treatment ^[4][1].
• HPP: This condition presents as severe hemolytic anemia, meaning the red blood cells are destroyed faster than the body can replace them ^[9][10]. Symptoms often begin at birth, with infants showing severe jaundice and anemia ^[9][10].

Managing HPP Long-Term

While HPP can be life-threatening in early infancy and feel overwhelming for parents, the long-term outlook is generally positive with proper care. Over time, some HPP patients’ symptoms may “mellow” into a milder form that resembles typical HE, though the underlying genetic defect remains ^[9].

Treatment usually focuses on managing the anemia:

• Supportive Care: Doctors often prescribe daily folic acid (folate) supplements to help the body keep up with the rapid production of new red blood cells.
• Blood Transfusions: Regular transfusions may be needed, especially during infancy or times of illness ^[4][11].
• Splenectomy: In many cases, surgical removal of the spleen (splenectomy) is recommended ^[4][11]. Because the spleen is responsible for filtering out and destroying the fragile HPP cells, removing it usually significantly improves or resolves the severe anemia, even though the red blood cells will remain abnormally shaped. However, a splenectomy has lifelong implications, including an increased risk of certain infections, which requires ongoing vaccinations and preventive care.