Phosphomevalonate kinase deficiency expands the genetic spectrum of systemic autoinflammatory diseases

Abstract

In the isoprenoid biosynthesis pathway, mevalonate is phosphorylated in two subsequent enzyme steps by mevalonate kinase (MVK) and phosphomevalonate kinase (PMVK) to generate mevalonate pyrophosphate that is further metabolized to produce sterol and non-sterol isoprenoids. Biallelic pathogenic variants in the MVK gene result in the autoinflammatory metabolic disorder MVK Deficiency (MKD). So far, however, no patients with proven PMVK deficiency due to biallelic pathogenic variants in the PMVK gene have been reported. This study aims to report the first patient with functionally confirmed PMVK deficiency, including the clinical, biochemical and immunological consequences of a homozygous missense variant in the PMVK gene. We performed whole-exome sequencing and functional studies in cells from a patient who, upon clinical and immunological evaluation, was suspected of an autoinflammatory disease. We identified a homozygous PMVK p.Val131Ala (NM_006556.4: c.392T>C,) missense variant in our patient. Pathogenicity was supported by genetic algorithms and modeling analysis and confirmed in patient cells that revealed a markedly reduced PMVK enzyme activity due to a virtually complete absence of PMVK protein. Clinically, the patient showed various similarities, but also distinct features compared to MKD patients, and responded well to therapeutic IL-1 inhibition. In this study we report the first patient with proven PMVK deficiency due to a homozygous missense variant in PMVK leading to an autoinflammatory disease. PMVK deficiency expands the genetic spectrum of systemic autoinflammatory diseases (SAID), characterized by recurrent fevers, arthritis and cytopenia and thus should be included in the differential diagnosis and genetic testing for SAIDs.