Clinical phenotype and laboratory markers in patients affected by haploinsufficiency of A20 (HA20): a case series from two Italian centres

Introduction: Haploinsufficiency of A20 (HA20) is a monogenic disease caused by heterozygous TNFAIP3 variants. Despite the marked clinical variability, no genotype-phenotype correlation or validated laboratory biomarkers have been identified so far. Neurobehavioural abnormalities have been reported in murine models, but their prevalence in humans remains unclear. Objectives: To describe a cohort of patients with HA20 from two centres, evaluating age-related clinical variability; to assess the prevalence of neuropsychiatric symptoms; to explore the inflammatory profile of the patients, including interferon (IFN)-γ-inducible chemokines (CXCL9/10) and type 1 IFN signature (IS), as well as the therapies administered. Methods: Clinical and laboratory data of 17 subjects from six families heterozygous for TNFAIP3 variants (American College of Medical Genetics and Genomics class 4-5) were retrospectively collected. Disease activity, treatments, CXCL9/10 and IS levels were collected. Continuous variables were expressed as medians (IQR). Age at onset was compared using the Kruskal-Wallis test, and groups were compared through the Wilcoxon test or Fisher's exact test. Results: Clinical manifestations included oral aphthosis (88%), recurrent fever (53%), gastrointestinal inflammation (53%), autoimmunity (47%), genital ulcers (47%), neuropsychiatric symptoms (41%), arthritis/tenosynovitis (18%) and skin inflammation (12%). Disease onset before 5 years of age was associated with a higher prevalence of neuropsychiatric symptoms during lifetime (p=0.004), whereas arthritis was more common in patients with later onset. The median age at onset differed significantly according to the type of clinical manifestation (p<0.001). Higher IS levels were found in patients with active disease (p<0.01). Conclusions: HA20 shows marked clinical heterogeneity both between and within families. Clinical manifestations appear age-related and early disease onset was associated with increased neuropsychiatric involvement lifetime. Finally, type 1 IS may represent a potential biomarker of disease activity in HA20.