IFIH1 deficiency causing neonatal herpes simplex virus encephalitis and recurrent retinitis

Abstract

Homozygous loss-of-function variants in Interferon induced with helicase C domain 1 (IFIH1) leads to immunodeficiency with early onset recurrent and severe viral respiratory infections (Immunodeficiency 95; MIM 619773). Severe respiratory infections with RNA viruses such as rhinovirus and respiratory syncytial virus (RSV) are most characteristic of IFIH1 deficiency. IFIH1 encodes melanoma differentiation-associated protein 5 (MDA5), an intracellular sensor of mainly long double-stranded RNA (ds-RNA), a viral replication intermediate. When activated, MDA5 triggers antiviral pathways including increased transcription of Type 1-interferon. The antiviral role of MDA5 is best described for positive (+) RNA viruses such as Picornavirus family which produce long ds-RNA as a replication intermediate. We present a patient with neonatal herpes simplex virus (HSV) encephalitis and recurrent retinitis with homozygous variant of unknown significance (VUS) in IFIH1, c.2062A>G (p.Lys688Glu).Patient is a 10-year-old male, born of consanguineous parents from the United Arab Emirates. Past medical history is notable for neonatal HSV encephalitis, grade 3 intraventricular hemorrhage, cerebral palsy, epilepsy, optic atrophy and recurrent HSV retinitis. Patient has no additional history of severe or recurrent infections. No family history of recurrent or severe infections, malignancy, autoimmunity or autoinflammation.Immune evaluation demonstrated anemia with elevated mean corpuscular volume and mild elevation of platelets and monocytes. Patient had normal lymphocyte subsets, normal T and B cell subset distributions, protective vaccine titers and normal immunoglobins apart from mildly elevated immunoglobulin G. An Invitae primary immunodeficiency panel demonstrated homozygous VUS in IFIH1, c.2062A>G (p.Lys688Glu). This variant is not found in gnomAD or ClinVar and has a Combined Annotation Dependent Depletion score of 22.6. Functional testing demonstrated decreased interferon induction after stimulation with intracellular RNA, intracellular DNA and agonists of both Toll-like receptor 7 and 9. These findings are consistent with MDA5 deficiency given decreased interferon response with known MDA5 agonists.In summary, we describe a patient with recurrent and severe infections with a DNA virus and no known infections with respiratory RNA viruses. Both DNA and RNA viruses produce long ds-RNA as replication intermediates, an MDA5 agonist. This patient highlights the anti-viral role of MDA5 for both DNA and RNA viruses.