The A20 protein, encoded by the TNFAIP3 gene, is involved in the negative regulation of the NF-κB signalling pathway. Loss-of-function mutations in TNFAIP3 cause A20 haploinsufficiency (HA20), which predisposes to autoinflammatory diseases such as Behçet's disease, JIA and SLE. Neurological involvement is very rare in HA20. An 11-year-old male patient was admitted to our hospital with complaints of headache, behavioural changes and decreased academic performance that started after he had COVID-19 infection at the age of 9. On neurological examination, left nasolabial sulcus was faint, DTRs were brisk and pathological reflexes were present, other system examinations were normal. Brain MRI was compatible with encephalitis. He was hospitalised with a prediagnosis of viral/autoimmune encephalitis (AIE) and received IVIG and antibiotherapy. Six months and 11 months after discharge, he presented with seizures two more times. In both admissions, newly developing cortical lesions were present on brain MRI and he was treated with the diagnosis of recurrent AIE. WES performed for possible immunodysregulation revealed a homozygous mutation (c.607C>T) in the TNFAIP3 gene. Overactivation of the NF-κB signalling pathway was shown in functional analyses. Monthly IVIG treatment was started with plans to start anti-IL-6 treatment and prepare for bone marrow transplantation. To date, neurological involvement in HA20 has only been reported in a few cases as CNS vasculitis. With this case with biallelic mutation, recurrent AIE and the autosomal recessive form of the disease were described for the first time in HA20 patients, thus expanding the clinical spectrum of the disease.

Ibrahim Oncel
Hacettepe University Faculty of Medicine
Turkey

Orhan Ozdogan
Hacettepe University Faculty of Medicine
Turkey

Ismail Yaz
Hacettepe University Faculty of Medicine
Turkey

Saliha Esenboga
Hacettepe University Faculty of Medicine
Turkey

Sevil Oskay
Hacettepe University Faculty of Medicine
Turkey

Deniz Cagdas Ayvaz
Hacettepe University Faculty of Medicine
Turkey