JAM2: A New Culprit at the Pathophysiology of Primary Familial Brain Calcification.

Primary familial brain calcification (PFBC) is an uncommon degenerative neurological disease that can be hereditary or sporadic, and manifests equally in both sexes and at any age. Several studies initially identified variants in four different genes as the cause of the disorder, all with an autosomal dominant inheritance pattern: SLC20A2, PDGFRB, PDGFB and XPR1. However, there have been reports of the involvement of additional genes in the autosomal recessive inheritance pattern, such as MYORG and more recently JAM2, suggesting that the deregulation of the neurovascular unit (NVU) is important in the pathogenesis of PFBC. The recent study by Schottlaender and collaborators (2020) has added new data to foster these analyses and to enable a better understanding of this underdiagnosed and intriguing neuropsychiatric condition. A great challenge now is to design a model that explains how different pathways might lead to similar neuroimaging findings but with variable clinical outcome, and with marked severity in cases linked to MYORG and JAM2. Currently available databases of detailed gene expression in different vascular cell types from the mouse brain could be used to explore a possible integrative model.

Overlapping Diseases in a Brazilian Subject with Brain Calcification Linked to Novel Phenotypes.

Primary familial brain calcification (PFBC) is a well-known genetic condition that has recently had a surge of autosomal recessive cases. We recently reported a case of autosomal recessive PFBC on a 54-year-old Brazilian patient with a novel homozygous variant on MYORG. Interestingly, that patient also had a series of uncommon signs and symptoms, including Hashimoto's thyroiditis, polyneuropathy, optic nerve head drusen (ONHD), and persistent anemia. We chose to perform whole exome sequencing (WES) to possibly detect other unknown genetic conditions that could explain the extra-neurological findings reported. WES confirmed the presence of the MYORG variant previously reported by us, and determined the presence of a heterozygous nonsense variant on HBB (c.118C > T, p.Q40*), defining a diagnosis of beta-thalassemia. Based on literature review, the new WES finding explains the persistent anemia and polyneuropathy shown by the patient, while still leaving the ONHD and autoimmune thyroiditis without a clear genetic link. This way, we propose that these novel clinical findings could be linked to MYORG, but still encourage further studies to evaluate this possibility.