X-Linked Sideroblastic Anaemia Caused by Intronic ALAS2 Variant Resulting in Highly Variable Expressive Phenotype in Male Siblings, a Case Report.

X-linked sideroblastic anaemia (XLSA) is a rare hereditary disorder caused by mutations in the ALAS2 gene, essential for haem biosynthesis. We report two male siblings, the first of whom developed severe microcytic hypochromic anaemia requiring regular transfusions, iron chelation and an allogeneic bone marrow transplant, while his brother displayed only mild microcytic hypochromic indices without anaemia. Initial genetic screening did not identify a pathogenic variant. However, duo exome sequencing later revealed an intronic ALAS2 mutation, initially categorised as of uncertain significance and subsequently reclassified as pathogenic. This case underscores the diagnostic challenges posed by intronic mutations and the highly variable expressivity of XLSA, even among siblings. Trial Registration: The authors have confirmed clinical trial registration is not needed for this submission.