Factor XIII Deficiency: Laboratory, Molecular, and Clinical Aspects.

Factor XIII-A (FXIII-A) deficiency is an ultra-rare bleeding disorder characterized by high rates of morbidity and mortality, primarily resulting from intracranial hemorrhage, umbilical cord bleeding, and miscarriage, whereas patients with severe FXIII-B deficiency present with a milder phenotype. Although the estimated incidence of severe FXIII-A deficiency is one per 2 million, a high prevalence ranging from 0.8 to 3.5% has been observed for heterozygous FXIII-A deficiency. Unlike most bleeding disorders, individuals with heterozygous FXIII-A deficiency, particularly women, are more likely to experience hemorrhagic complications during hemostatic challenges. About 200 Mutations have been observed in F13A and F13B genes, with most being missense mutations, while large deletions are the rarest. There is no correlation between genotype and phenotype, but a moderate to strong correlation between factor activity and clinical severity in FXIII-A deficiency difficult. 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.