Factor XIII Deficiency: Laboratory, Molecular, and Clinical Aspects

genes, with most being missense mutations, while large deletions are the rarest. There is no correlation between genotype and phenotype and a moderate to strong correlation between factor activity and clinical severity in FXIII-A deficiency, making it difficult to predict bleeding patterns based on genotype and FXIII activity levels. Primary prophylaxis is mandatory for all patients with severe FXIII-A deficiency, while those with heterozygous deficiency are generally asymptomatic and may require on-demand therapy during hemostatic challenges, most commonly in women. On the other hand, patients with severe FXIII-B deficiency may only require on-demand therapy, while heterozygotes are generally asymptomatic. Although there are general recommended therapeutic regimens for prophylaxis or on-demand therapy in different situations, personalized pharmacokinetic-based replacement therapy represents the optimal approach that can optimize intervention efficacy. In such an approach, several factors may affect the effectiveness of treatment and determine the dose and type of intervention, including the classification of FXIII deficiency, residual plasma levels of FXIII, clinical situation requiring intervention, age, weight, and also gender.