Congenital sideroblastic anemias (CSA) are a group of rare disorders characterized by abnormal iron utilization during erythropoiesis, leading to mitochondrial iron overload, the formation of ring sideroblasts, and ineffective erythropoiesis resulting in anemia. Ring sideroblasts are erythroid precursors that contain non-heme iron deposits in their mitochondria, forming a distinctive ring-like pattern around the nucleus. Mitochondria are double membrane organelle provide a large amount of energy for cellular activities, by the process of oxidative phosphorylation (OXPHOS). The role of mitochondria has been well described in erythropoiesis. CSA exhibits clinical heterogeneity, affecting only the erythroid system in some cases, while in others presenting as part of broader syndromic conditions. Their molecular basis remains imperfectly known, although the development of next- generation sequencing technology brought tremendous advances in the understanding of their genetic features. More than 20 genes have been identified as causative of CSA, with all modes of inheritance observed: X-linked recessive, autosomal dominant, autosomal recessive, pseudo- dominant, and mitochondrial. These genes are typically involved in one of four key mitochondrial pathways: i) Heme biosynthesis (e.g., ALAS2, SLC25A38); ii) Iron-sulfur cluster biosynthesis and transport (e.g., GLRX5, HSPA9, HSCB); iii) tRNA synthesis and maturation (e.g., PUS1, YARS2, LARS2, IARS2, SARS2, MARS1, TRNT1); iv) Mitochondrial respiratory chain synthesis (e.g., NDUFB11).

However, in nearly 30% of cases within the French CSA cohort, the underlying genetic cause remains unknown. In these patients with molecularly unexplained whole genome or exome sequencing approaches focusing on genes involved in mitochondrial function and iron metabolism identified several possibly pathogenic variants in CSA patients. These genes were not clearly described as playing a role in erythropoiesis or heme or iron metabolism. We hope to confirm their role in CSA. However, in nearly 30% of cases within the French CSA cohort , the underlying genetic cause remains unknown. The investigators hope to confirm the role in CSA of gene identified with exome sequencing approaches.

Inclusion Criteria:

• Patient with unexplained congenital sideroblastic anemia on the molecular side with the gene panels used routinely
• Patients already identified by exome sequencing approach carrying bi-allelic variants of candidate genes of the mitochondrial respiratory pathway.
• Patients meeting the same criteria who will be identified prospectively over the next 12 months

Exclusion Criteria:

• NA