Why Does CHH Cause Macrocytic Anemia and How Is It Treated?

Macrocytic anemia in cartilage-hair hypoplasia (CHH) occurs because a mutation in the RMRP gene slows down the assembly of the body’s cellular protein factories ^[1][2]. This heavily impacts fast-dividing cells like red blood cells, which rely on rapid protein production to grow and multiply ^[3][4]. Because the cells cannot divide properly, they become abnormally large (macrocytic) and dysfunctional ^[4]. Treatment does not cure the genetic cause but instead focuses on close monitoring by a specialist, nutritional support, and blood transfusions to maintain healthy red blood cell levels ^[5].

The Cause: Protein Factories and Fast-Dividing Cells

To understand why CHH causes macrocytic anemia, it helps to look at how cells are built. CHH is caused by changes (mutations) in the RMRP gene ^[1][6]. Rather than acting as a blueprint for a physical structural part of the cell, this gene provides the instructions for a tool that helps assemble the cell’s ribosomes, which act as the cellular protein factories ^[4][7].

In CHH, the RMRP mutation causes these protein factories to assemble incorrectly or work too slowly ^[2]. This slowdown, often called a ribosomopathy, affects the entire body but is especially hard on cells that need to divide very quickly ^[3].

Red blood cell precursors (the young cells in your bone marrow that will eventually become mature red blood cells) are among the fastest-dividing cells in the human body ^[4]. They have an incredibly high demand for new proteins ^[3]. When their protein factories cannot keep up with this demand, the cells struggle to divide. Instead of splitting into normal, healthy red blood cells, they grow abnormally large and become stuck in development ^[4][3]. This results in fewer red blood cells circulating in the body (anemia), and the ones that do circulate are oversized (macrocytic).

Note: In the general public, macrocytic anemia is most often caused by a severe lack of Vitamin B12 or folate ^[5]. However, in CHH, the macrocytic anemia is driven by the underlying genetics ^[5][1]. While standard vitamin supplements will not fix the defective protein factories, they are still important to ensure a nutritional deficiency isn’t making the genetic anemia worse ^[5].

Symptoms to Watch For

Because macrocytic anemia reduces the oxygen-carrying capacity of your blood, it can cause noticeable daily symptoms. You should contact your care team if you experience:

• Unusual or worsening fatigue
• Shortness of breath, especially after mild activity
• Pale skin, particularly around the lips, nail beds, or inner eyelids
• Dizziness, lightheadedness, or persistent “brain fog”

Treatment and Management Options

Because the anemia in CHH is tied to the patient’s genetics, treatments are designed to manage symptoms, support the body, and prevent complications ^[5]. Your care is typically guided by a hematologist (a doctor specializing in blood disorders) working alongside your geneticist and primary care provider. They may recommend:

• Active Monitoring: Routine blood tests (such as a complete blood count, or CBC) are used to track red blood cell counts, cell size, and overall immune function ^[5][8]. The frequency varies, but tests are often done every few months or annually depending on your baseline levels and symptoms.
• Nutritional Support: Doctors will often test for and treat any co-existing nutritional deficiencies (like low B12, folate, or iron) to ensure that your red blood cells have all the raw materials they need to function as well as possible ^[5].
• Blood Transfusions: If anemia becomes severe or causes significant symptoms, red blood cell transfusions may be given to supply the body with healthy, properly sized cells ^[5].
• Iron Chelation Therapy: If a patient requires multiple, ongoing blood transfusions, iron can begin to build up to dangerous levels in the organs ^[5]. Iron chelation involves taking medication that binds to excess iron and helps the body flush it out ^[5].
• Stem Cell Transplantation: In rare, severe cases where the bone marrow stops producing blood cells entirely (bone marrow failure) or if there is life-threatening immune dysfunction, a hematopoietic stem cell transplant (bone marrow transplant) may be considered ^[9][10]. This extreme intervention replaces the defective bone marrow with healthy cells from a donor, though it is often pursued primarily to treat the severe immune complications of CHH rather than just the anemia alone.