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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Hematology · Autosomal Recessive Congenital Sideroblastic Anemia

The Biology of Heme and Genetic Variants

At a Glance

Autosomal recessive congenital sideroblastic anemia results from inherited variants that disrupt heme production in developing red blood cells. Iron then accumulates in mitochondria, forming ring sideroblasts; the specific gene helps guide family testing and care.

To understand Autosomal Recessive Congenital Sideroblastic Anemia (ARCSA), it helps to imagine the mitochondria inside a developing red blood cell (an erythroblast in the bone marrow) as a high-precision factory. This factory’s main job is to build heme, the specialized molecule that holds onto oxygen so it can be carried through the body [1]. In a healthy erythroblast, iron is brought into this mitochondrial factory and combined with other ingredients to create heme. In ARCSA, the factory is disrupted by an inherited genetic variant, causing the iron to pile up inside the bone marrow cell like unused raw materials [2][3].

The Heme Factory and Its Parts

The process of making heme is complex and requires several different “tools” and “transporters” to work in perfect harmony.

  • The Ingredients: One of the primary ingredients for heme is an amino acid called glycine.
  • The Assembly: An enzyme called ALAS2 acts as the gatekeeper, starting the assembly process by combining glycine with other molecules [4].
  • The Finished Product: Finally, iron is added to the mixture to complete the heme molecule.

In ARCSA, one or more of these steps fails. Because the heme cannot be finished, the iron that was supposed to be used has nowhere to go. It becomes trapped inside the mitochondria, forming a distinctive “ring” of iron that doctors can see under a microscope. These are called ring sideroblasts [3][5].

The Genes Behind the Breakdowns

Because this is an autosomal recessive condition, a child must inherit a variant of the gene from both parents [6]. Recurrence Risk: If both biological parents are confirmed carriers of a pathogenic variant in the same gene, each future pregnancy has a 25% chance of being affected, a 50% chance of being a carrier, and a 25% chance of inheriting neither variant. Siblings may need targeted testing, and a genetic counselor can discuss reproductive options.

Different genes cause the assembly line to fail in different ways:

  • SLC25A38 (The Most Common): This gene acts as the delivery truck for glycine. When it is mutated, glycine cannot get into the mitochondrial factory. Without glycine, the assembly line stops before it even begins [4][6].
  • GLRX5: This gene helps manage iron-sulfur clusters, which are essential for several enzymes in the heme factory to work properly. If GLRX5 is broken, the enzymes lose their “tools,” and the factory shuts down [7][8].
  • HSPA9: This gene works as a “chaperone,” helping other proteins in the factory reach their correct positions. If it fails, the assembly line becomes disorganized [9].
  • PUS1 and TRNT1: These genes are involved in the “instruction manuals” (tRNAs) that the factory uses to build its machinery. When these fail, the cell can’t even build the tools it needs to make heme [10][11]. Variants in these genes can cause “syndromic” disease, meaning they may affect muscles, hearing, or the immune system in addition to the blood, though this depends entirely on the specific variant and the individual [12][13].

Why This Is Different from Other Anemias

It is critical to distinguish ARCSA from other conditions that might look similar on a blood test:

Condition Cause Key Difference
ARCSA Genetic variants (e.g., SLC25A38) Inherited from parents; usually present from birth [6].
X-Linked (ALAS2) Variant on the X chromosome Usually affects males; often responds well to supervised Vitamin B6 [14][15].
Acquired (MDS) DNA changes that happen over time Usually occurs in older adults; not inherited. Diagnosed by integrating morphology, cytogenetics, and clinical context [16].
Toxic (Lead/Zinc) Environmental exposure Caused by lead poisoning or excessive zinc; requires prompt environmental/medical evaluation [16][17].
Nutritional Copper or B6 deficiency Requires medical evaluation. Never self-treat with high-dose B6, iron, or copper as this can cause nerve damage or severe toxicity [18].

Because this is a genetic condition, it isn’t caused by anything the parents did or didn’t do during pregnancy, and it isn’t something that can be fixed with a simple change in diet. In fact, taking iron supplements without doctor approval is dangerous for ARCSA patients. Understanding the specific gene involved is the key to managing the condition and predicting how it might affect the rest of the body [13][19].

Common questions in this guide

What causes autosomal recessive congenital sideroblastic anemia?
ARCSA occurs when a child inherits a disease-causing variant in the same heme-related gene from both biological parents. The variant disrupts heme production in developing red blood cells; the condition is not caused by anything the parents did during pregnancy or by a simple dietary change.
What do ring sideroblasts mean on a bone marrow examination?
Ring sideroblasts are developing red blood cells with iron trapped in their mitochondria in a ring around the nucleus. They form when heme production fails and are an important clue to sideroblastic anemia.
Which genes can cause ARCSA?
The page identifies SLC25A38 as the most common gene discussed, along with GLRX5, HSPA9, PUS1, and TRNT1. PUS1 and TRNT1 variants can sometimes cause effects beyond the blood, such as muscle, hearing, or immune-system problems, depending on the specific variant.
What are the chances that a future child will have ARCSA if both parents are carriers?
For each future pregnancy, there is a 25% chance the child will be affected, a 50% chance the child will be a carrier, and a 25% chance the child will inherit neither variant. A genetic counselor can explain testing and reproductive options for the family.
How does ARCSA differ from other sideroblastic anemias?
ARCSA is caused by inherited genetic variants and is usually present from birth. X-linked disease involving ALAS2 often affects males and may respond to supervised vitamin B6, whereas acquired myelodysplastic syndrome develops over time and toxic or nutritional forms are linked to exposures or deficiencies.
Can ARCSA affect organs besides the blood?
Some gene variants linked to ARCSA can affect other systems, but this depends on the exact gene and variant. PUS1 and TRNT1 variants may be associated with muscle, hearing, or immune-system problems, so the treating team may consider broader evaluation.
Should someone with ARCSA take iron or high-dose vitamin B6?
Do not start iron, high-dose vitamin B6, or copper unless a clinician recommends it. Iron supplements may be dangerous when iron is already accumulating, excessive vitamin B6 can damage nerves, and copper can also cause severe toxicity.

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References

References (19)
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This page is for informational purposes only and does not constitute medical advice. A hematologist or genetic counselor can interpret ARCSA genetic results and discuss testing, treatment, and reproductive options for your family.

Guide contents Anemia, sideroblastic, pyridoxine-responsive, autosomal recessive
Research & Literature
01 Understanding Your Child's Rare Diagnosis 03 Proving the Diagnosis