Familial hemophagocytic lymphohistiocytosis (FHL) is a life-threatening hyperinflammatory disorder caused by inherited defects in lymphocyte cytotoxicity. Because patients are generally asymptomatic before disease onset, preemptive therapeutic intervention remains difficult. However, the existence of fetal-onset cases and cases without an apparent infectious trigger suggests that molecular abnormalities may already be present before overt clinical manifestations. To date, pre-onset studies in FHL have been limited largely to neonatal samples from unaffected siblings, and analyses using multiple patient samples have been challenging.
To characterize the preclinical disease state of FHL using proteomic analysis of neonatal dried blood spots (DBS) and to explore the potential applicability of this approach to newborn screening for FHL and other inborn errors of immunity.
Using an optimized high-efficiency DBS proteomics platform, we analyzed archived neonatal DBS samples collected through routine newborn screening from 8 patients with FHL type 3 and 1 patient with FHL type 2. Proteomic profiles were compared with those of 90 healthy neonates to evaluate alterations in disease-causing molecules and related biological pathways.
In patients with FHL3, expression of Munc13-4, the causative protein encoded by UNC13D, was significantly reduced, and this decrease was detectable in neonatal DBS obtained before clinical onset. Pathway analysis based on differentially expressed proteins further suggested that, in addition to neutrophil degranulation, pathways related to lipid metabolism and inflammatory responses—some of which are known to be activated after disease onset—were already dysregulated during the neonatal period.
DBS-based proteomic analysis can detect disease-associated protein abnormalities and pathogenic pathway alterations in neonatal samples from patients with FHL before symptom onset. Accumulation of pre-onset DBS proteomic data may deepen our understanding of the pathophysiology of FHL and other inherited disorders, while also supporting the development of novel diagnostic and newborn screening strategies.
