Identification of expanded repeats in NOTCH2NLC in neurodegenerative dementias

Highlights

• The GGC repeat expansions in the NOTCH2NLC gene were identified in patients with.AD and FTD.

• Of cases with repeats expansions, three showed leukoencephalopathy in T2-Flair imaging.

• The repeat expansions in NOTCH2NLC may be associated with AD or FTD-like phenotypes as well as leukoencephalopathy.

Abstract

Recently, the (GGC)_n repeat expansion in the NOTCH2NLC gene has been identified to be associated with neuronal intranuclear inclusion disease (NIID). Given the clinical overlap of dementia-dominant NIID with neurodegenerative dementia, we therefore hypothesized that the NOTCH2NLC repeat expansion might also contribute to these diseases. In the present study, repeat primed polymerase chain reaction (RP-PCR) and GC-rich PCR were conducted to detect the repeats of NOTCH2NLC in a cohort of 1004 patients with neurodegenerative dementias from mainland China. As a result, 4 sporadic patients were found to carry the NOTCH2NLC repeats expansion, totally accounting for 0.4% of all dementia individuals, and the accurate repeated sizes were 110, 133,120 and 76 respectively. Of 4 mutation carriers, three and one were clinically diagnosed Alzheimer's disease (AD) and frontotemporal dementia (FTD) respectively. In addition, 3 out of them revealed leukoencephalopathy in T2-Flair imaging. This study revealed that although rare, the NOTCH2NLC repeat expansions may be associated with AD or FTD-like phenotype as well as leukoencephalopathy.

Introduction

The neurodegenerative dementias are characterized by clinically heterogeneous, progressive and irreversible diseases with frequently overlapping symptoms, such as multi-cognitive impairments, behavior variants and movement deficits. It mainly involves Alzheimer's disease (AD), dementia of Lewy bodies (DLB), frontotemporal dementia (FTD), and vascular dementia (VaD). Among them, AD is the leading cause of dementia in the elderly, comprising 50%–75% of all dementias, followed by VaD, accounting for 15%, while FTD and DLB were responsible for 10% and 7.5% respectively (Hinz and Geschwind, 2017, Hogan et al., 2016, O'Brien and Thomas, 2015, Vann Jones and O'Brien, 2014).

Over the last few decades, with the genetic technology development, substantial progress has been made in understanding the molecular genetics of neurodegenerative dementias. The continuous findings of dementia associated pathogenic genes provided the possibility of genetic testing for the diagnosis of dementia in clinical practice. Among these genes, β-amyloid precursor protein (APP), presenilin-1 (PSEN1) and presenilin-2 (PSEN2) have so far been recognized as 3 causative genes for familial AD. The estimated mutation frequencies of these 3 genes are 6% for PSEN1, 1% for APP, and 1% for PSEN2, which totally explained a genetic background of only 5%–10% of early-onset AD (EOAD, younger than 65 years) (Cacace et al., 2016, Loy et al., 2014). Genetic etiology has also been revealed in 30%–40% of FTD patients with a positive family history (Rademakers and Rovelet-Lecrux, 2009). To date, more than 20 genes have been identified in FTD patients, among which the microtubule associated protein tau (MAPT), progranulin (GRN), and chromosome 9 open reading frame 72 (C9orf72) represented the key-players of inherited FTD (Fostinelli et al., 2018, Wood et al., 2013). In contrast, the genetic architecture of DLB seemed much tougher to be found. Deficits in Parkinson disease (PD) genes, like glucosylceramidase beta (GBA), leucine rich repeat kinase 2 (LRRK2), and synuclein alpha/beta (SNCA/SNCB) have been reported in patients with DLB (Orme et al., 2018). With regard to VaD, the most frequent was cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), caused by notch receptor 3 (NOTCH3), and other genes, like galactosidase alpha (GLA), 3 prime repair exonuclease 1 (TREX1), collagen type IV alpha 1 chain (COL4A1) and HtrA serine peptidase 1 (HTRA1), were also reported in VaD patients (Ikram et al., 2017). However, there still a large proportion of dementia patients unexplained from genetic perspective, and the novel associated genes need to be found in dementia patients.

Neuronal intranuclear inclusion disease (NIID), a rare neurodegenerative disease with extensive phenotypic heterogeneity, was characterized pathologically by the presence of eosinophilic intranuclear inclusions in the central, peripheral, autonomic nervous systems, and visceral organs (Sone et al., 2016, Takahashi-Fujigasaki, 2003). The age at onset of NIID varied widely, which was divided into 3 forms: infant, juvenile, and adult forms (Takahashi-Fujigasaki, 2003). The manifestations of adult-onset NIID patients primarily included cognitive decline, peripheral neuropathy, autonomic dysfunction, cerebellar ataxia, parkinsonism, seizure, stroke-like episodes, encephalitic episodes, and paroxysmal disturbance of consciousness (Fujita et al., 2017, Michaud and Gilbert, 1981, Munoz-Garcia and Ludwin, 1986, O'Sullivan et al., 2000, Shindo et al., 2019, Sone et al., 2005). However, of these complicated phenotypes, cognitive impairment has been recognized as the most common presentation either in familial or sporadic adult-onset NIID. Patients with dementia-dominant NIID could present with memory impairment, disorientation, visuospatial, language and execution dysfunction, as well as abnormal behaviors, like repetitive outbursts of violence, wandering aimlessly, and absentmindedly standing naked et al. (Araki et al., 2016, Sone et al., 2014, Takahashi-Fujigasaki et al., 2016, Yamaguchi et al., 2018), which were, to some extent, clinically overlapped with AD and other neurodegenerative dementias, thus easily being misdiagnosed in clinical practice.

Recently, our team, together with another cohort from Japan, described a trinucleotide (GGC)_n expanded repeats in the 5′ UTR region of Notch 2 N-terminal like C (NOTCH2NLC) gene was linked to NIID using long-read genome sequencing (LRS) approach (Sone et al., 2019, Tian et al., 2019). Although lacking of a definite boundary of pathogenic repeats, Tian et al. reported patients with NIID, diagnosed by skin pathology, carried at least 66 repeats (Tian et al., 2019). Since the clinical characterization of dementia-dominant NIID and neurodegenerative dementia were overlapped, we therefore, would detect the NOTCH2NLC repeats in a cohort of patients with neurodegenerative dementias.