Albertine Donker

Chapter 10 340 relationship. In two brothers we found a novel c.1412G>A (p.Cys471Tyr) variant. Despite the results of the different bio-informatic tools that were not consistent in its prediction of pathogenicity, we considered this ALAS2 variant as pathogenic since both brothers shared the same phenotype of microcytic anemia and iron overload. Of note, the two affected brothers had no unaffected brothers without the relevant ALAS2 variant. This would have supported our hypothesis concerning its pathogenicity. Although XLSA is an X-linked disease, we illustrate that female carriers of an ALAS2 defect may develop a phenotype of sideroblastic anemia later in life, probably due to a predominant inactivation of the normal X-chromosome and physiological age- related skewed X-inactivation in hematopoietic cells. Regarding effect of treatment, we observed an increase in Hb in one of our patients after commencement of phlebotomies, illustrating that blood drawing not only benefits the reduction of systemic iron overload but may also improve erythropoiesis in XLSA patients. We ended our article with practical recommendations for the clinician regarding a timely diagnosis and adequate treatment of probands with XLSA in combination with accurate screening of relatives, in order to reduce the disease burden for the individual patient and to avoid lifelong sequelae of iron deficiency or iron overload for both the proband and the possibly affected relatives. PART II: DIAGNOSTICSTUDIES: FOCUSON IRONREFRACTORY IRONDEFICIENCY ANEMIA For the second part of this thesis we performed studies aimed at improving the diagnosis of microcytic disorders due to disorders of iron metabolism, with the focus on IRIDA. In Chapter 7 we described a study on ranges of serum hepcidin in healthy children with the objective of facilitating the diagnosis of iron disorders in childhood. We measured serum hepcidin-25 levels in 266 healthy Dutch children, aged 0.3-17 years, attending the day care unit of the Máxima MC, Veldhoven, the Netherlands for minor surgical or diagnostic procedures. We used an isotope dilution mass spectrometry hepcidin assay, standardized with our commutable 2 nd reference material (RM), assigned by a candidate primary RM. Since we aimed to cover the different key periods of human growth and development for both sexes, we divided our study population in subgroups for age and sex; infancy and toddler stage (0-<2 years), early childhood (2-<6 years), middle childhood (6 -<12 years) and adolescence (12-17 years). We constructed age- and sex-specific values for serum hepcidin and its ratio