| Classic textbook neurology teaches that amyotrophic lateral sclerosis (ALS) is a degenerative disease that selectively affects upper and lower motor neurons and is fatal 3-5 years after onset-a description which suggests that the clinical presentation of ALS is very homogenous. However, clinical and postmortem observations, as well as genetic studies, demonstrate that there is considerable variability in the phenotypic expression of ALS. Here, we review the phenotypic variability of ALS and how it is reflected in familial and sporadic ALS, in the degree of upper and lower motor neuron involvement, in motor and extramotor involvement, and in the spectrum of ALS and frontotemporal dementia. Furthermore, we discuss some unusual clinical characteristics regarding presentation, age at onset and disease progression. Finally, we address the importance of this variability for understanding the pathogenesis of ALS and for the development of therapeutic strategies.

The exact mechanism underlying amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) associated with the GGG GCC repeat expansion in C9orf72 is still unclear. Two gain-of-function mechanisms are possible: repeat RNA toxicity and dipeptide repeat protein (DPR) toxicity. We here dissected both possibilities using a zebrafish model for ALS. Expression of two DPRs, glycine-arginine and proline-arginine, induced a motor axonopathy. Similarly, expanded sense and antisense repeat RNA also induced a motor axonopathy and formed mainly cytoplasmic RNA foci. However, DPRs were not detected in these conditions. Moreover, stop codon-interrupted repeat RNA still induced a motor axonopathy and a synergistic role of low levels of DPRs was excluded. Altogether, these results show that repeat RNA toxicity is independent of DPR formation. This RNA toxicity, but not the DPR toxicity, was attenuated by the RNA-binding protein Pur-alpha and the autophagy-related protein p62. Our findings demonstrate that RNA toxicity, independent of DPR toxicity, can contribute to the pathogenesis of C9orf72-associated ALS/FTD.

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Several neurodegenerative disorders like amyotrophic lateral sclerosis (ALS) and spinocerebellar ataxia (SCA) are caused by non‐coding nucleotide repeat expansions. Different pathogenic mechanisms may underlie these non‐coding repeat expansion disorders. While gain‐of‐function mechanisms, such as toxicity associated with expression of repeat RNA or toxicity associated with repeat‐associated non‐ATG (RAN) products, are most frequently connected with these disorders, loss‐of‐function mechanisms have also been implicated. We review the different pathways that have been linked to non‐coding repeat expansion disorders such as C9ORF72‐linked ALS/frontotemporal dementia (FTD), myotonic dystrophy, fragile X tremor/ataxia syndrome (FXTAS), SCA, and Huntington's disease‐like 2. We discuss modes of RNA toxicity focusing on the identity and the interacting partners of the toxic RNA species. Using the C9ORF72 ALS/FTD paradigm, we further explore the efforts and different methods used to disentangle RNA vs. RAN toxicity. Overall, we conclude that there is ample evidence for a role of RNA toxicity in non‐coding repeat expansion diseases.

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As scaling becomes increasingly difficult, 3D integration has emerged as a viable alternative to achieve the requisite bandwidth and power efficiency challenges. However mechanical stress induced by the through silicon vias (TSV) is one of the key constraints in the 3D flow that must be controlled in order to preserve the integrity of front end devices. For the first time an extended and comprehensive study is given for the stress induced by single-and arrayed TSVs and its impact on both analog and digital FEOL devices and circuits. This work provides a complete experimental assessment and quantifies the stress distribution and its effect on front end devices. By using a combined experimental and theoretical approach we provide a framework that will enable stress aware design and the right definition of keep out zone and ultimately save valuable silicon area.

We report for the first time the demonstration of 3D integrated circuits obtained by die-to-die stacking using Cu Through Silicon Vias (TSV). The Cu TSV process is inserted between contact and M1 of our reference 0.13µm CMOS process on 200mm wafers. The top die is thinned down to 25µm and bonded to the landing wafer by Cu-Cu thermo-compression. Both top and landing wafers contain CMOS finished at M2 to evaluate the process impact both FEOL and BEOL. The results confirm no degradation of the FEOL performance. The functionality of various ring oscillator topologies that include inverters distributed over both top and bottom dies connected through TSVs demonstrates excellent chip integrity after the TSV and 3D stacking process. 3D-SIC processRecently 3D integration has gained a lot of interest due to its potential to alleviate some important performance limitations facing CMOS scaling and because it enables so-called heterogeneous integration [1][2]. Different approaches to 3D integration are reported depending on system level requirements [3]. Our 3D Stacked IC (3D-SIC) process [4][5] uses IC foundry infrastructure to create Through Silicon Vias (TSVs) prior to BEOL processing. The main advantage of this approach is the fact that it has minimal impact on both FEOL and BEOL design and processing. Furthermore it offers very high TSV densities. The TSV process sequence is summarized in Fig. 1. Figure 1: Schematic of the 3D-SIC Through Silicon Via (TSV) module.After processing of the CMOS FEOL and the PMD stack, we patterned TSVs with a diameter of 5µm and a pitch of 10µm using a 3µm thick I-line resist. We performed an undercut free, resist-based TSV etch (Fig. 2); undercut underneath the contact layer is avoided by pre-deposition of a polymer on the sidewall of the etched PMD/STI stack prior to the Si etch. For electrical isolation, we deposit a 100nm SACVD O 3 -TEOS layer. The metallization sequence consists of applying a 80nm PVD Ta barrier and a 300nm PVD Cu seed followed by an ECD via fill using a 3-component plating chemistry. Finally the Cu overburden is polished in a top-side TSV CMP step (Fig. 3). After this process, we apply a standard, 2 metal layer BEOL process to finalize the top Si-die. Figure 2&3: FIB through TSV in vicinity of device after etch, strip& clean (left), and after TSV CMP and sintering (right). (Pt on top for contrast).After wafer test, the wafer is mounted on a temporary carrier and thinned down to a Si-thickness of ~25 m by a combination of grinding and CMP. In this process, the TSVs are exposed on the wafer backside. Next the Si is recessed by dry etching over a distance of ~700nm with respect to the copper TSV. In this work the dies were then stacked by Cu-Cu thermo-compression bonding in a Die-to-Die (D2D) fashion, although compatibility with Die-to-Wafer integration remains. Figure 4 shows an optical 3D reconstruction of the obtained 3D stack. Figure 4: Optical 3D reconstruction based on multiple images at different height of thinned top die stacked to a bottom die by Cu-Cu bonding.

A repeat expansion in C9orf72 is responsible for the characteristic neurodegeneration in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in a still unresolved manner. Proposed mechanisms involve gain-of-functions, comprising RNA and protein toxicity, and loss-of-function of the C9orf72 gene. Their exact contribution is still inconclusive and reports regarding loss-of-function are rather inconsistent. Here, we review the function of the C9orf72 protein and its relevance in disease. We explore the potential link between reduced C9orf72 levels and disease phenotypes in postmortem, in vitro, and in vivo models. Moreover, the significance of loss-of-function in other non-coding repeat expansion diseases is used to clarify its contribution in C9orf72 ALS/FTD. In conclusion, with evidence pointing to a multiple-hit model, loss-of-function on itself seems to be insufficient to cause neurodegeneration in C9orf72 ALS/FTD.