Aberrant nucleic acids generated during viral replication are the main trigger for antiviral immunity, and mutations disrupting nucleic acid metabolism can lead to autoinflammatory disorders. Here we investigated the etiology of X-linked reticulate pigmentary disorder (XLPDR), a primary immunodeficiency with autoinflammatory features. We discovered that XLPDR is caused by an intronic mutation that disrupts expression of POLA1, the gene encoding the catalytic subunit of DNA polymerase-α. Unexpectedly, POLA1 deficiency results in increased type I interferon production. This enzyme is necessary for RNA:DNA primer synthesis during DNA replication and strikingly, POLA1 is also required for the synthesis of cytosolic RNA:DNA, which directly modulates interferon activation. Altogether, this work identified POLA1 as a critical regulator of the type I interferon response.

Mothers giving care to children with RTT are at high risk of severe depression and lower HRQoL scores of domains that reflect mental well-being. Results of this study can help in planning subsequent interventions directed at families dealing with Rett syndrome.

Objective Citrullinemia type 1 (CTLN1) is an inherited metabolic disease affecting the brain which is detectable by newborn screening. The clinical spectrum is highly variable including individuals with lethal hyperammonemic encephalopathy in the newborn period and individuals with a mild‐to‐moderate or asymptomatic disease course. Since the phenotypic severity has not been predictable early during the disease course so far, we aimed to design a reliable disease prediction model. Methods We used a newly established mammalian biallelic expression system to determine residual enzymatic activity of argininosuccinate synthetase 1 (ASS1; OMIM #215700) in 71 individuals with CTLN1, representing 48 ASS1 gene variants and 50 different, mostly compound heterozygous combinations in total. Residual enzymatic ASS1 activity was correlated to standardized biochemical and clinical endpoints available from the UCDC and E‐IMD databases. Results Residual enzymatic ASS1 activity correlates with peak plasma ammonium and L‐citrulline concentrations at initial presentation. Individuals with 8% of residual enzymatic ASS1 activity or less had more frequent and more severe hyperammonemic events and lower cognitive function than those above 8%, highlighting that residual enzymatic ASS1 activity allows reliable severity prediction. Noteworthy, empiric clinical practice of affected individuals is in line with the predicted disease severity supporting the notion of a risk stratification‐based guidance of therapeutic decision‐making based on residual enzymatic ASS1 activity in the future. Interpretation Residual enzymatic ASS1 activity reliably predicts the phenotypic severity in CTLN1. We propose a new severity‐adjusted classification system for individuals with CTLN1 based on the activity results of the newly established biallelic expression system.

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