Genotype–Phenotype Correlation in a Couple in Which the Wife Is a Carrier of the Beta-Thalassemia Trait and the Husband Is a Carrier of a Mutation in the ALAS2 Gene: Both Gene Defects Are Associated with Non-Iron-Deficiency Microcytic Anemia

Abstract

Introduction: Generally, microcytic anaemia is caused by sideropenia or a genetic gap. The suspicion that microcytic anaemia is caused by a genetic gap must always be considered in the face of an inadequate response to martial therapy. The aim of this paper is to highlight how biochemical diagnosis alone is sometimes not sufficient to understand the cause of microcytic anaemia. For this reason, for a correct genotype–phenotype correlation, it is essential to identify the defective gene underlying the microcytic anaemia. Detailed Case Description: This case concerns a married couple who both have microcytic anaemia. They came to our attention because the lady, pregnant at 12 weeks, underwent screening for chromosomal abnormalities using combined tests in the first trimester of pregnancy. A biochemical screening performed ten years earlier showed that both spouses were healthy carriers of the beta-thalassemia trait. A careful analysis of the biochemical data and an in-depth molecular diagnosis of the alpha and beta globin genes showed that the woman was a healthy carrier of the beta-thalassemia trait while the husband was a healthy carrier of a mutation in the ALAS2 gene. Analysis of the biochemical data of her husband and family members revealed that she had X-linked microcytic sideroblastic anaemia caused by an alteration in the function of the ALAS2 (5′-Aminolevulinate Synthase 2) gene located on the short arm of the X chromosome (Xp11.21). Discussion and Conclusions: This result is very relevant as, during genetic counselling, we explained to the couple that invasive prenatal diagnosis was not necessary as there is no risk of procreating a transfusion-dependent individual.