Primary familial brain calcification is a monogenic disease characterized by bilateral calcifications in the basal ganglia and other brain regions, and commonly presents motor, psychiatric, and cognitive symptoms. Currently, four autosomal dominant (SLC20A2, PDGFRB, PDGFB, XPR1) and one autosomal recessive (MYORG) causative genes have been identified. Compared with patients with autosomal dominant primary familial brain calcification, patients with the recessive form of the disease present with more severe clinical and imaging phenotypes, and deserve more clinical and research attention. Biallelic mutations in MYORG cannot explain all autosomal recessive primary familial brain calcification cases, indicating the existence of novel autosomal recessive genes. Using homozygosity mapping and whole genome sequencing, we detected a homozygous frameshift mutation (c.140delT, p.L48*) in the JAM2 gene in a consanguineous family with two affected siblings diagnosed with primary familial brain calcification. Further genetic screening in a cohort of 398 probands detected a homozygous start codon mutation (c.1A>G, p.M1?) and compound heterozygous mutations [c.504G>C, p.W168C and c.(67+1_68-1)_(394+1_395-1), p.Y23_V131delinsL], respectively, in two unrelated families. The clinical phenotypes of the four patients included parkinsonism (3/4), dysarthria (3/4), seizures (1/4), and probable asymptomatic (1/4), with diverse onset ages. All patients presented with severe calcifications in the cortex in addition to extensive calcifications in multiple brain areas (lenticular nuclei, caudate nuclei, thalamus, cerebellar hemispheres, ± brainstem; total calcification scores: 43–77). JAM2 encodes junctional adhesion molecule 2, which is highly expressed in neurovascular unit-related cell types (endothelial cells and astrocytes) and is predominantly localized on the plasma membrane. It may be important in cell-cell adhesion and maintaining homeostasis in the CNS. In Chinese hamster ovary cells, truncated His-tagged JAM2 proteins were detected by western blot following transfection of p.Y23_V131delinsL mutant plasmid, while no protein was detected following transfection of p.L48* or p.1M? mutant plasmids. In immunofluorescence experiments, the p.W168C mutant JAM2 protein failed to translocate to the plasma membrane. We speculated that mutant JAM2 protein resulted in impaired cell-cell adhesion functions and reduced integrity of the neurovascular unit. This is similar to the mechanisms of other causative genes for primary familial brain calcification or brain calcification syndromes (e.g. PDGFRB, PDGFB, MYORG, JAM3, and OCLN), all of which are highly expressed and functionally important in the neurovascular unit. Our study identifies a novel causative gene for primary familial brain calcification, whose vital function and high expression in the neurovascular unit further supports impairment of the neurovascular unit as the root of primary familial brain calcification pathogenesis.

BackgroundIntronic pentanucleotide insertion in the sterile alpha motif domain‐containing 12 gene was recently identified as the genetic cause of familial cortical myoclonic tremor with epilepsy type 1.ObjectivesWe thereafter conducted a multimodal MRI research to further understand familial cortical myoclonic tremor with epilepsy type 1.MethodsWe enrolled 31 patients carrying heterozygous pathogenic intronic pentanucleotide insertion in the sterile alpha motif domain‐containing 12 gene and 31 age‐ and sex‐matched healthy controls. We compared multimodal MRI metrics, including voxel‐based morphometry, fractional anisotropy of diffuse tensor imaging, frequency‐dependent percent amplitude fluctuation, and seed‐based functional connectivity of resting‐state functional MRI.ResultsSignificant decreased gray matter volume was found in the cerebellum. Percent amplitude fluctuation analysis showed significant interaction effect of “Frequency by Group” in three regions, including the vermis VIII, left cerebellar lobule VIII, and left precentral gyrus. Specifically, the lowest‐frequency band exhibited significant increased percent amplitude fluctuation in patients in the two cerebellar subregions, whereas the highest‐frequency band exhibited decreased percent amplitude fluctuation in the precentral gyrus in patients. Discriminative analysis by support vector machine showed a mean accuracy of 82% (P = 1.0–5). An increased functional connectivity between vermis VIII and the left precentral gyrus was found in patients with familial cortical myoclonic tremor with epilepsy type 1. A positive correlation between the percent amplitude fluctuation in the left cerebellar lobule VIII and duration of cortical tremor was also found.ConclusionThe cerebellum showed both structural and functional damages. The distinct change of spontaneous brain activity, that is, increased ultra‐low‐frequency amplitude in the cerebellum and the decreased higher‐frequency amplitude in the motor cortex, might be a pathophysiological feature of familial cortical myoclonic tremor with epilepsy type 1. © 2020 International Parkinson and Movement Disorder Society

A BS TRACT: Background: Biallelic mutations in the MYORG gene were first identified as the cause of recessively inherited primary familial brain calcification. Interestingly, some heterozygous carriers also exhibited brain calcifications.Objectives: To further investigate the role of single heterozygous MYORG mutations in the development of brain calcifications. Methods: A nation-wide cohort of Chinese primary familial brain calcification probands was enrolled from March 2016 ---

Background and purpose The GGC repeat expansion in the NOTCH2NLC gene has been identified as the genetic cause of neuronal intranuclear inclusion disease (NIID). Recently, this repeat expansion was also reported to be associated with essential tremor (ET). However, some patients with this repeat expansion, initially diagnosed with ET, were eventually diagnosed with NIID. Therefore, controversy remains regarding the clinical diagnosis of these expansion‐positive patients presenting with tremor‐dominant symptoms. This study aimed to clarify the clinical phenotype in tremor‐dominant patients who have the GGC repeat expansion in the NOTCH2NLC gene. Methods We screened for pathogenic GGC repeat expansions in 602 patients initially diagnosed with ET and systematically re‐evaluated the clinical features of the expansion‐positive probands and their family members. Results Pathogenic GGC repeat expansion in the NOTCH2NLC gene was detected in 10 probands (1.66%). Seven of these probands were re‐evaluated and found to have systemic areflexia, cognitive impairment, and abnormal nerve conduction, which prompted a change of diagnosis from ET to NIID. Three of the probands had typical hyperintensity in the corticomedullary junction on diffusion‐weighted imaging. Intranuclear inclusions were detected in all four probands who underwent skin biopsy. Conclusions The NIID tremor‐dominant subtype can be easily misdiagnosed as ET. We should take NIID into account for differential diagnosis of ET. Systemic areflexia could be an important clinical clue suggesting that cranial magnetic resonance imaging examination, or even further genetic testing and skin biopsy examination, should be used to confirm the diagnosis of NIID.

Background Intronic (TTTCA)n insertions in the SAMD12, TNRC6A, and RAPGEF2 genes have been identified as causes of familial cortical myoclonic tremor with epilepsy. Objective To identify the cause of familial cortical myoclonic tremor with epilepsy pedigrees without (TTTCA)n insertions in SAMD12, TNRC6A, and RAPGEF2. Methods Repeat‐primed polymerase chain reaction, long‐range polymerase chain reaction, and Sanger sequencing were performed to identify the existence of a novel (TTTGA)n insertion. Targeted long‐read sequencing was performed to confirm the accurate structure of the (TTTGA)n insertion. Results We identified a novel expanded intronic (TTTGA)n insertion at the same site as the previously reported (TTTCA)n insertion in SAMD12. This insertion cosegregated with familial cortical myoclonic tremor with epilepsy in 1 Chinese pedigree with no (TTTCA)n insertion. In the targeted long‐read sequencing of 2 patients and 1 asymptomatic carrier in this pedigree, with 1 previously reported (TTTCA)n‐insertion–carrying patient as a positive control, a respective total of 302, 159, 207, and 50 on‐target subreads (predicated accuracy: ≥90%) spanning the target repeat expansion region were generated. These sequencing data revealed the accurate repeat expansion structures as (TTTTA)114‐123(TTTGA)108‐116 in the pedigree and (TTTTA)38(TTTCA)479 in (TTTCA)n‐insertion–carrying patient. Conclusion The targeted long‐read sequencing helped us to elucidate the accurate structures of the (TTTGA)n and (TTTCA)n insertions. Our finding offers a novel possible cause for familial cortical myoclonic tremor with epilepsy and might shed light on the identification of genetic causes of this disease in pedigrees with no detected (TTTCA)n insertion in the reported causative genes. © 2019 International Parkinson and Movement Disorder Society