RRP12 Variants Are Associated With Autosomal Recessive Brain Calcifications.

BACKGROUND

Primary brain calcifications are observed in several inherited diseases due to different pathogenic mechanisms, including the disruption of the neurovascular unit, mitochondrial dysfunction, and impaired nucleic acid metabolism.

OBJECTIVE

The aim of the study was to identify a novel genetic cause of brain calcifications in genetically unresolved cases.

METHODS

Exome sequencing data from two unrelated Pakistani patients with generalized dystonia and primary brain calcifications were analyzed. The best candidate gene (ie, RRP12) was then investigated in two large cohorts of patients with brain calcifications from France (n = 111) and China (n = 543). RRP12 loss-of-function phenotype was explored through Western blot and immunocytofluorescence studies on patient-derived fibroblasts and in a knockdown zebrafish model.

RESULTS

A combined approach of exome sequencing and homozygosity mapping allowed the prioritization of a rare homozygous variant in RRP12 (c.1558C>T, p.R520C) in two apparently unrelated Pakistani patients from consanguineous families, presenting with infantile-onset generalized dystonia, spasticity, and widespread brain calcifications. Screening of two large cohorts of patients with unresolved brain calcifications revealed two affected French siblings and one unrelated Chinese individual, each carrying rare, biallelic, missense variants in the RRP12 gene (c.1429G>A, p.E477K and c.2634T>G, p.F878L, respectively). Molecular studies revealed a significant reduction in RRP12 protein and abnormal nucleolar morphology in patient'derived fibroblasts. Consistent with its essential role in RNA metabolism, rrp12 knockdown in zebrafish caused severe developmental delay, crimping, and early lethality.

CONCLUSIONS

RRP12 is a novel candidate gene for autosomal recessive brain calcifications, possibly associated with a wide clinical spectrum ranging from early-onset severe forms to adult-onset paucisymptomatic presentations. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.