An autosomal dominant cerebellar ataxia linked to chromosome 16q22.1 is associated with a single-nucleotide substitution in the 5' untranslated region of the gene encoding a protein with spectrin repeat and Rho guanine-nucleotide exchange-factor domains

Genome-wide analyses identify 21 infertility loci and over 400 reproductive hormone loci across the allele frequency spectrum

Genome-wide association studies (GWASs) may help inform treatments for infertility, whose causes remain unknown in many cases. Here we present GWAS meta-analyses across six cohorts for male and female infertility in up to 41,200 cases and 687,005 controls. We identified 21 genetic risk loci for infertility (P≤5E-08), of which 12 have not been reported for any reproductive condition. We found positive genetic correlations between endometriosis and all-cause female infertility (rg=0.585, P=8.98E-14), and between polycystic ovary syndrome and anovulatory infertility (rg=0.403, P=2.16E-03). The evolutionary persistence of female infertility-risk alleles in EBAG9 may be explained by recent directional selection. We additionally identified up to 269 genetic loci associated with follicle-stimulating hormone (FSH), luteinising hormone, oestradiol, and testosterone through sex-specific GWAS meta-analyses (N=6,095-246,862). While hormone-associated variants near FSHB and ARL14EP colocalised with signals for anovulatory infertility, we found no rg between female infertility and reproductive hormones (P>0.05). Exome sequencing analyses in the UK Biobank (N=197,340) revealed that women carrying testosterone-lowering rare variants in GPC2 were at higher risk of infertility (OR=2.63, P=1.25E-03). Taken together, our results suggest that while individual genes associated with hormone regulation may be relevant for fertility, there is limited genetic evidence for correlation between reproductive hormones and infertility at the population level. We provide the first comprehensive view of the genetic architecture of infertility across multiple diagnostic criteria in men and women, and characterise its relationship to other health conditions.

Spinocerebellar ataxia type 31 (SCA31)

Spinocerebellar ataxia type 31 (SCA31) is one of the most common forms of autosomal-dominant cerebellar ataxia in Japan. SCA31 has a strong founder effect, which is consistent with the fact that this disease is basically absent in other ethnicities. After searching the entire founder region of a 2-megabase (Mb), we finally identified a 2.5 to 3.8 kb-long complex penta-nucleotide repeat containing (TGGAA)n, (TAGAA)n, (TAAAA)n and (TAAAATAGAA)n as the only genetic change segregating SCA31 individuals from normal people. Furthermore, (TGGAA)n was isolated as the only repeat explaining the pathogenesis because other repeats were encountered in control Japanese. From the genomic point of view, the complex penta-nucleotide repeat lies in an intronic segment shared by two genes, BEAN1 (brain expressed, associated with Nedd4) and TK2 (thymidine kinase 2) transcribed in mutually opposite directions. While TK2 is ubiquitously expressed, BEAN1 is transcribed only in the brain. Thus, the complex repeat is bi-directionally transcribed exclusively in the brain, as two independent non-coding repeats. Furthermore, the complex repeat containing (UGGAA)n was found to form abnormal RNA structures, called RNA foci, in cerebellar Purkinje cell nuclei of SCA31 patients' brains. Subsequent investigation by over-expressing (UGGAA)n in Drosophila revealed that the RNA containing (UGGAA)n exerts toxicity in a length- and expression level-dependent manner, whereas its toxicity could be dampened by (UGGAA)n-binding proteins, TDP-43, FUS and hnRNP A2/B1. It seems rational to formulate a treatment strategy through enhancing the role of RNA-binding proteins against (UGGAA)n-toxicity in SCA31.

Spinocerebellar ataxia type 31: A clinical and radiological literature review

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant disease, classified amongst pure cerebellar ataxias (ADCA type 3). While SCA31 is the third most prevalent autosomal dominant ataxia in Japan, it is extremely rare in other countries. A literature review was conducted on PubMed, where we included all case reports and studies describing the clinical presentation of original SCA31 cases. The clinical and radiological features of 374 patients issued from 25 studies were collected. This review revealed that the average age of onset was 59.1 ± 3.3 years, with symptoms of slowly progressing ataxia and dysarthria. Other common clinical features were oculomotor dysfunction (38.8%), dysphagia (22.1%), hypoacousia (23.3%), vibratory hypoesthesia (24.3%), and dysreflexia (41.6%). Unfrequently, abnormal movements (7.4%), extrapyramidal symptoms (4.5%) and cognitive impairment (6.9%) may be observed. Upon radiological examination, clinicians can expect a high prevalence of cerebellar atrophy (78.7%), occasionally accompanied by brainstem (9.1%) and cortical (9.1%) atrophy. Although SCA31 is described as a slowly progressive pure cerebellar syndrome characterized by cerebellar signs such as ataxia, dysarthria and oculomotor dysfunction, this study evaluated a high prevalence of extracerebellar manifestations. Extracerebellar signs were observed in 52.5% of patients, primarily consisting of dysreflexia, vibratory hypoesthesia and hypoacousia. Nonetheless, we must consider the old age and longstanding disease course of patients as a confounding factor for extracerebellar sign development, as some may not be directly attributable to SCA31. Clinicians should consider SCA31 in patients with a hereditary, pure cerebellar syndrome and in patients with extracerebellar signs.

Rapid and comprehensive diagnostic method for repeat expansion diseases using nanopore sequencing

We developed a diagnostic method for repeat expansion diseases using a long-read sequencer to improve currently available, low throughput diagnostic methods. We employed the real-time target enrichment system of the nanopore GridION sequencer using the adaptive sampling option, in which software-based target assignment is available without prior sample enrichment, and built an analysis pipeline that prioritized the disease-causing loci. Twenty-two patients with various neurological and neuromuscular diseases, including 12 with genetically diagnosed repeat expansion diseases and 10 manifesting cerebellar ataxia, but without genetic diagnosis, were analyzed. We first sequenced the 12 molecularly diagnosed patients and accurately confirmed expanded repeats in all with uniform depth of coverage across the loci. Next, we applied our method and a conventional method to 10 molecularly undiagnosed patients. Our method corrected inaccurate diagnoses of two patients by the conventional method. Our method is superior to conventional diagnostic methods in terms of speed, accuracy, and comprehensiveness.

Whole-genome sequencing analysis of semi-supercentenarians

Extreme longevity is the paradigm of healthy aging as individuals who reached the extreme decades of human life avoided or largely postponed all major age-related diseases. In this study, we sequenced at high coverage (90X) the whole genome of 81 semi-supercentenarians and supercentenarians [105+/110+] (mean age: 106.6 ± 1.6) and of 36 healthy unrelated geographically matched controls (mean age 68.0 ± 5.9) recruited in Italy. The results showed that 105+/110+ are characterized by a peculiar genetic background associated with efficient DNA repair mechanisms, as evidenced by both germline data (common and rare variants) and somatic mutations patterns (lower mutation load if compared to younger healthy controls). Results were replicated in a second independent cohort of 333 Italian centenarians and 358 geographically matched controls. The genetics of 105+/110+ identified DNA repair and clonal haematopoiesis as crucial players for healthy aging and for the protection from cardiovascular events.

Rho Family GTPases and Rho GEFs in Glucose Homeostasis

Dysregulation of glucose homeostasis leading to metabolic syndrome and type 2 diabetes is the cause of an increasing world health crisis. New intriguing roles have emerged for Rho family GTPases and their Rho guanine nucleotide exchange factor (GEF) activators in the regulation of glucose homeostasis. This review summates the current knowledge, focusing in particular on the roles of Rho GEFs in the processes of glucose-stimulated insulin secretion by pancreatic β cells and insulin-stimulated glucose uptake into skeletal muscle and adipose tissues. We discuss the ten Rho GEFs that are known so far to regulate glucose homeostasis, nine of which are in mammals, and one is in yeast. Among the mammalian Rho GEFs, P-Rex1, Vav2, Vav3, Tiam1, Kalirin and Plekhg4 were shown to mediate the insulin-stimulated translocation of the glucose transporter GLUT4 to the plasma membrane and/or insulin-stimulated glucose uptake in skeletal muscle or adipose tissue. The Rho GEFs P-Rex1, Vav2, Tiam1 and β-PIX were found to control the glucose-stimulated release of insulin by pancreatic β cells. In vivo studies demonstrated the involvement of the Rho GEFs P-Rex2, Vav2, Vav3 and PDZ-RhoGEF in glucose tolerance and/or insulin sensitivity, with deletion of these GEFs either contributing to the development of metabolic syndrome or protecting from it. This research is in its infancy. Considering that over 80 Rho GEFs exist, it is likely that future research will identify more roles for Rho GEFs in glucose homeostasis.

Midbrain atrophy related to parkinsonism in a non-coding repeat expansion disorder: five cases of spinocerebellar ataxia type 31 with nigrostriatal dopaminergic dysfunction

Background

Spinocerebellar ataxia type 31 (SCA31) is caused by non-coding pentanucleotide repeat expansions in the BEAN1 gene. Clinically, SCA31 is characterized by late adult-onset, pure cerebellar ataxia. To explore the association between parkinsonism and SCA31, five patients with SCA31 with concomitant nigrostriatal dopaminergic dysfunction (NSDD) development, including three cases of L-DOPA responsive parkinsonism, were analyzed.

Methods

To assess regional brain atrophy, cross-sectional and longitudinal imaging analyses were retrospectively performed using magnetic resonance imaging (MRI) planimetry. The midbrain-to-pons (M/P) area ratio and cerebellar area were measured on midsagittal T1-weighted MRI in five patients with SCA31 with concomitant NSDD (NSDD(+)), 14 patients with SCA31 without NSDD (NSDD(−)), 32 patients with Parkinson’s disease (PD), and 15 patients with progressive supranuclear palsy (PSP). Longitudinal changes in the M/P area ratio were assessed by serial MRI of NSDD(+) (n = 5) and NSDD(−) (n = 9).

Results

The clinical characteristics assessed in the five patients with NSDD were as follows: the mean age at NSDD onset (72.0 ± 10.8 years), prominence of bradykinesia/akinesia (5/5), rigidity (4/5), tremor (2/5), dysautonomia (0/5), vertical gaze limitation (1/5), and abnormalities on ¹²³I-ioflupane dopamine transporter scintigraphy (3/3) and 3-Tesla neuromelanin MRI (4/4). A clear reduction in the midbrain area and the M/P area ratio was observed in the NSDD(+) group (p < 0.05) while there was no significant difference in disease duration or in the pons area among the NSDD(+), NSDD(−), and PD groups. There was also a significant difference in the midbrain and pons area between NSDD(+) and PSP (p < 0.05). Thus, mild but significant midbrain atrophy was observed in NSDD(+). A faster rate of decline in the midbrain area and the M/P area ratio was evident in NSDD(+) (p < 0.05).

Conclusion

The clinical characteristics of the five patients with SCA31 with concomitant NSDD, together with the topographical pattern of atrophy, were inconsistent with PD, PSP, and multiple system atrophy, suggesting that SCA31 may manifest NSDD in association with the pathomechanisms underlying SCA31.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40673-021-00134-4.

The guanine nucleotide exchange factor FLJ00068 activates Rac1 in adipocyte insulin signaling

Insulin stimulates glucose uptake via the translocation of the glucose transporter GLUT4 to the plasma membrane in adipocytes. Several lines of evidence suggest that the small GTPase Rac1 plays an important role in insulin-stimulated glucose uptake in skeletal muscle and adipocytes. The purpose of this study is to investigate the mechanisms whereby Rac1 is regulated in adipocyte insulin signaling. Here, we show that knockdown of the guanine nucleotide exchange factor FLJ00068 inhibits Rac1 activation and GLUT4 translocation by insulin and a constitutively activated form of the protein kinase Akt2. Furthermore, constitutively activated FLJ00068 induced Rac1 activation and Rac1-dependent GLUT4 translocation. Collectively, these results suggest the involvement of FLJ00068 downstream of Akt2 in insulin-stimulated glucose uptake signaling in adipocytes.

Molecular Mechanisms and Future Therapeutics for Spinocerebellar Ataxia Type 31 (SCA31)

Spinocerebellar ataxia type 31 (SCA31) is one of the autosomal-dominant neurodegenerative disorders that shows progressive cerebellar ataxia as a cardinal symptom. This disease is caused by a 2.5- to 3.8-kb-long complex pentanucleotide repeat containing (TGGAA)n, (TAGAA)n, (TAAAA)n, and (TAAAATAGAA)n in an intron of the gene called BEAN1 (brain expressed, associated with Nedd4). By comparing various pentanucleotide repeats in this particular locus among control Japanese and Caucasian populations, it was found that (TGGAA)n was the only sequence segregating with SCA31, strongly suggesting the pathogenicity of (TGGAA)n. The complex repeat also lies in an intron of another gene, TK2 (thymidine kinase 2), which is transcribed in the opposite direction, indicating that the complex repeat is bi-directionally transcribed as noncoding repeats. In SCA31 human brains, (UGGAA)n, the BEAN1 transcript of SCA31 mutation was found to form abnormal RNA structures called RNA foci in cerebellar Purkinje cell nuclei. Subsequent RNA pulldown analysis disclosed that (UGGAA)n binds to RNA-binding proteins TDP-43, FUS, and hnRNP A2/B1. In fact, TDP-43 was found to co-localize with RNA foci in human SCA31 Purkinje cells. To dissect the pathogenesis of (UGGAA)n in SCA31, we generated transgenic fly models of SCA31 by overexpressing SCA31 complex pentanucleotide repeats in Drosophila. We found that the toxicity of (UGGAA)n is length- and expression level-dependent, and it was dampened by co-expressing TDP-43, FUS, and hnRNP A2/B1. Further investigation revealed that TDP-43 ameliorates (UGGAA)n toxicity by directly fixing the abnormal structure of (UGGAA)n. This led us to propose that TDP-43 acts as an RNA chaperone against toxic (UGGAA)n. Further research on the role of RNA-binding proteins as RNA chaperones may provide a novel therapeutic strategy for SCA31.

Repeat-associated non-AUG (RAN) translation: insights from pathology

More than 40 different neurological diseases are caused by microsatellite repeat expansions. Since the discovery of repeat-associated non-AUG (RAN) translation by Zu et al. in 2011, nine expansion disorders have been identified as RAN-positive diseases. RAN proteins are translated from different types of nucleotide repeat expansions and can be produced from both sense and antisense transcripts. In some diseases, RAN proteins have been shown to accumulate in affected brain regions. Here we review the pathological and molecular aspects associated with RAN protein accumulation for each particular disorder, the correlation between disease pathology and the available in vivo models and the common aspects shared by some of the newly discovered RAN proteins.

Regulators of Rho GTPases in the Nervous System: Molecular Implication in Axon Guidance and Neurological Disorders

One of the fundamental steps during development of the nervous system is the formation of proper connections between neurons and their target cells-a process called neural wiring, failure of which causes neurological disorders ranging from autism to Down's syndrome. Axons navigate through the complex environment of a developing embryo toward their targets, which can be far away from their cell bodies. Successful implementation of neuronal wiring, which is crucial for fulfillment of all behavioral functions, is achieved through an intimate interplay between axon guidance and neural activity. In this review, our focus will be on axon pathfinding and the implication of some of its downstream molecular components in neurological disorders. More precisely, we will talk about axon guidance and the molecules implicated in this process. After, we will briefly review the Rho family of small GTPases, their regulators, and their involvement in downstream signaling pathways of the axon guidance cues/receptor complexes. We will then proceed to the final and main part of this review, where we will thoroughly comment on the implication of the regulators for Rho GTPases-GEFs (Guanine nucleotide Exchange Factors) and GAPs (GTPase-activating Proteins)-in neurological diseases and disorders.

Sequence configuration of spinocerebellar ataxia type 8 repeat expansions in a Japanese cohort of 797 ataxia subjects

Spinocerebellar ataxia type 8 (SCA8), an autosomal dominant neurodegenerative disorder showing slowly progressive cerebellar ataxia, is caused by a tri-nucleotide CTG repeat expansion (CTGexp) in the SCA8 gene. As the CTGexp is not fully penetrant, the significance of screening CTGexp in ataxia subjects remains obscure. We tested SCA8 CTGexp in a cohort of 797 ataxia subjects, and if present, its sequence configuration was analyzed. CTGexp was found in 16 alleles from 14 individuals, 2 of which was homozygous for CTGexp. Nucleotide sequencing disclosed 3 types of CTGexp sequence configurations: uninterrupted CTGexp, tri-nucleotide CTA interruption and CCG interruption. The 2 individuals with homozygous expansions were both sporadic cases with clinical features compatible with SCA8, supporting gene dosage effect. Seven out of 14 CTGexp-positive subjects were also carriers of other SCA expansions [Machado-Joseph disease (n=1), SCA6 (n=3) and SCA31 (n=3)], whereas 7 others were not complicated with such major SCAs. Ages of onset in subjects with pure CTGexp tended to be earlier than those with interrupted CTGexp among the 7 subjects not complicated by major SCAs, suggesting that pure CTGexp have stronger pathogenic effect than interrupted CTGexps. The present study underscores importance of disclosing sequence configuration when testing SCA8.

Inter-generational instability of inserted repeats during transmission in spinocerebellar ataxia type 31

The causative mutation for spinocerebellar ataxia type 31 (SCA31) is an intronic insertion containing pathogenic pentanucleotide repeats, (TGGAA)_n. We examined to what degree the inserted repeats were unstable during transmission. In 14 parent-child pairs, the average change of onset age was -6.4±7.3 years (mean±s.d.) in the child generation when compared with the parent generation. Of the 11 pairs analyzed, six showed expansion of inserted repeat length during transmission, and five showed contraction. On average, the inserted repeats expanded by 12.2±32.7 bp during transmission, but their mean length (with a 95% confidence interval) was not significantly different between parent and child generations. We consider that the length of the inserted repeats in SCA31 is changeable during transmission, but inter-generational instability is not marked, as far as the current sizing method can determine.

Rac1 Activation Caused by Membrane Translocation of a Guanine Nucleotide Exchange Factor in Akt2-Mediated Insulin Signaling in Mouse Skeletal Muscle

Insulin-stimulated glucose uptake in skeletal muscle is mediated by the glucose transporter GLUT4, which is translocated to the plasma membrane following insulin stimulation. Several lines of evidence suggested that the protein kinase Akt2 plays a key role in this insulin action. The small GTPase Rac1 has also been implicated as a regulator of insulin-stimulated GLUT4 translocation, acting downstream of Akt2. However, the mechanisms whereby Akt2 regulates Rac1 activity remain obscure. The guanine nucleotide exchange factor FLJ00068 has been identified as a direct regulator of Rac1 in Akt2-mediated signaling, but its characterization was performed mostly in cultured myoblasts. Here, we provide in vivo evidence that FLJ00068 indeed acts downstream of Akt2 as a Rac1 regulator by using mouse skeletal muscle. Small interfering RNA knockdown of FLJ00068 markedly diminished GLUT4 translocation to the sarcolemma following insulin administration or ectopic expression of a constitutively activated mutant of either phosphoinositide 3-kinase or Akt2. Additionally, insulin and these constitutively activated mutants caused the activation of Rac1 as shown by immunofluorescent microscopy using a polypeptide probe specific to activated Rac1 in isolated gastrocnemius muscle fibers and frozen sections of gastrocnemius muscle. This Rac1 activation was also abrogated by FLJ00068 knockdown. Furthermore, we observed translocation of FLJ00068 to the cell periphery following insulin stimulation in cultured myoblasts. Localization of FLJ00068 in the plasma membrane in insulin-stimulated, but not unstimulated, myoblasts and mouse gastrocnemius muscle was further affirmed by subcellular fractionation and subsequent immunoblotting. Collectively, these results strongly support a critical role of FLJ00068 in Akt2-mediated Rac1 activation in mouse skeletal muscle insulin signaling.

Spontaneous shaker rat mutant - a new model for X-linked tremor/ataxia

The shaker rat is an X-linked recessive spontaneous model of progressive Purkinje cell (PC) degeneration exhibiting a shaking ataxia and wide stance. Generation of Wistar Furth (WF)/Brown Norwegian (BN) F1 hybrids and genetic mapping of F2 sib-sib offspring using polymorphic markers narrowed the candidate gene region to 26 Mbp denoted by the last recombinant genetic marker DXRat21 at 133 Mbp to qter (the end of the long arm). In the WF background, the shaker mutation has complete penetrance, results in a stereotypic phenotype and there is a narrow window for age of disease onset; by contrast, the F2 hybrid phenotype was more varied, with a later age of onset and likely non-penetrance of the mutation. By deep RNA-sequencing, five variants were found in the candidate region; four were novel without known annotation. One of the variants caused an arginine (R) to cysteine (C) change at codon 35 of the ATPase, Ca²⁺ transporting, plasma membrane 3 (Atp2b3) gene encoding PMCA3 that has high expression in the cerebellum. The variant was well supported by hundreds of overlapping reads, and was found in 100% of all affected replicas and 0% of the wild-type (WT) replicas. The mutation segregated with disease in all affected animals and the amino acid change was found in an evolutionarily conserved region of PMCA3. Despite strong genetic evidence for pathogenicity, in vitro analyses of PMCA3^R35C function did not show any differences to WT PMCA3. Because Atp2b3 mutation leads to congenital ataxia in humans, the identified Atp2b3 missense change in the shaker rat presents a good candidate for the shaker rat phenotype based on genetic criteria, but cannot yet be considered a definite pathogenic variant owing to lack of functional changes.

Summary: The shaker rat mutant: a new model for essential tremors and ataxia characterized by Purkinje cell degeneration.

The chromosome 16q-linked autosomal dominant cerebellar ataxia (16q-ADCA): A newly identified degenerative ataxia in Japan showing peculiar morphological changes of the Purkinje cell: The 50th Anniversary of Japanese Society of Neuropathology

The chromosome 16q22.1-linked autosomal-dominant cerebellar ataxia (16q-ADCA) is a form of spinocerebellar ataxia (SCA) common in Japan. It is clinically characterized by late-onset purely cerebellar ataxia. The neuropathologic hallmark of 16q-ADCA is degeneration of Purkinje cells accompanied by an eosinophilic structure which we named "halo-like amorphous materials". By immunohistochemistry and electron microscopy, the structure has been so far found to contain two components: the somatic sprouts from the Purkinje cells and presynaptic terminals of unknown origin. As far as we are aware, this peculiar morphological change of Purkinje cells has not been previously described. Further investigations may disclose unique pathological processes in SCA.

Neurons Rho to Get in Shape for the Day

Linking structural changes in neurons to animal behavior has proven challenging. New findings by Pesakou et al. tie daily cycles of axon arbor extension and retraction, mediated by Rho activity, to circadian and seasonal patterns of behavior in the fruit fly.

Circadian Rhythms in Rho1 Activity Regulate Neuronal Plasticity and Network Hierarchy

Neuronal plasticity helps animals learn from their environment. However, it is challenging to link specific changes in defined neurons to altered behavior. Here, we focus on circadian rhythms in the structure of the principal s-LNv clock neurons in Drosophila. By quantifying neuronal architecture, we observed that s-LNv structural plasticity changes the amount of axonal material in addition to cycles of fasciculation and defasciculation. We found that this is controlled by rhythmic Rho1 activity that retracts s-LNv axonal termini by increasing myosin phosphorylation and simultaneously changes the balance of pre-synaptic and dendritic markers. This plasticity is required to change clock network hierarchy and allow seasonal adaptation. Rhythms in Rho1 activity are controlled by clock-regulated transcription of Puratrophin-1-like (Pura), a Rho1 GEF. Since spinocerebellar ataxia is associated with mutations in human Puratrophin-1, our data support the idea that defective actin-related plasticity underlies this ataxia.

Regulating Rac in the nervous system: molecular function and disease implication of Rac GEFs and GAPs

Rho family GTPases, including RhoA, Rac1, and Cdc42 as the most studied members, are master regulators of actin cytoskeletal organization. Rho GTPases control various aspects of the nervous system and are associated with a number of neuropsychiatric and neurodegenerative diseases. The activity of Rho GTPases is controlled by two families of regulators, guanine nucleotide exchange factors (GEFs) as the activators and GTPase-activating proteins (GAPs) as the inhibitors. Through coordinated regulation by GEFs and GAPs, Rho GTPases act as converging signaling molecules that convey different upstream signals in the nervous system. So far, more than 70 members of either GEFs or GAPs of Rho GTPases have been identified in mammals, but only a small subset of them have well-known functions. Thus, characterization of important GEFs and GAPs in the nervous system is crucial for the understanding of spatiotemporal dynamics of Rho GTPase activity in different neuronal functions. In this review, we summarize the current understanding of GEFs and GAPs for Rac1, with emphasis on the molecular function and disease implication of these regulators in the nervous system.

Autopsy case of spinocerebellar ataxia type 31 with severe dementia at the terminal stage

Spinocerebellar ataxia type 31 (SCA31) is an autosomal dominant cerebellar ataxia commonly observed in Japan. However, few neuropathological examinations have been conducted. Here we report the case of a 76-year-old Japanese male SCA31 patient. He noticed dysarthria and difficulty walking at 65 years old. His symptoms subsequently deteriorated, although he could still walk with assistance at 70 years. At 73 years, when he could no longer walk, he was admitted to our hospital. He showed severe limb and truncal ataxia. His father and older brother had shown the same symptoms. Brain magnetic resonance imaging showed cerebellar atrophy of the anterior lobe and white matter hyperintensities. He was diagnosed with SCA31 by genetic analysis. Gradually, his cognitive functions and ability to communicate declined. He died of respiratory failure at the age of 76. Neuropathological examination revealed severe Purkinje cell loss that was accentuated in the anterior lobe of the cerebellum. Furthermore, the remaining Purkinje cells showed abnormal processes (that is, halo-like amorphous materials), as has been reported previously. Severe deposition of hyperphosphorylated tau-positive neurites, many senile plaques and amyloid angiopathy were observed in the neocortex. Our findings suggest that in SCA31, accelerated tau and amyloid pathology in the neocortex might induce dementia at the terminal stage.

RhoGEFs in cell motility: novel links between Rgnef and focal adhesion kinase

Rho guanine exchange factors (GEFs) are a large, diverse family of proteins defined by their ability to catalyze the exchange of GDP for GTP on small GTPase proteins such as Rho family members. GEFs act as integrators from varied intra- and extracellular sources to promote spatiotemporal activity of Rho GTPases that control signaling pathways regulating cell proliferation and movement. Here we review recent studies elucidating roles of RhoGEF proteins in cell motility. Emphasis is placed on Dbl-family GEFs and connections to development, integrin signaling to Rho GTPases regulating cell adhesion and movement, and how these signals may enhance tumor progression. Moreover, RhoGEFs have additional domains that confer distinctive functions or specificity. We will focus on a unique interaction between Rgnef (also termed Arhgef28 or p190RhoGEF) and focal adhesion kinase (FAK), a non-receptor tyrosine kinase that controls migration properties of normal and tumor cells. This Rgnef-FAK interaction activates canonical GEF-dependent RhoA GTPase activity to govern contractility and also functions as a scaffold in a GEF-independent manner to enhance FAK activation. Recent studies have also brought to light the importance of specific regions within the Rgnef pleckstrin homology (PH) domain for targeting the membrane. As revealed by ongoing Rgnef-FAK investigations, exploring GEF roles in cancer will yield fundamental new information on the molecular mechanisms promoting tumor spread and metastasis.

The emerging role of guanine nucleotide exchange factors in ALS and other neurodegenerative diseases

Small GTPases participate in a broad range of cellular processes such as proliferation, differentiation, and migration. The exchange of GDP for GTP resulting in the activation of these GTPases is catalyzed by a group of enzymes called guanine nucleotide exchange factors (GEFs), of which two classes: Dbl-related exchange factors and the more recently described dedicator of cytokinesis proteins family exchange factors. Increasingly, deregulation of normal GEF activity or function has been associated with a broad range of disease states, including neurodegeneration and neurodevelopmental disorders. In this review, we examine this evidence with special emphasis on the novel role of Rho guanine nucleotide exchange factor (RGNEF/p190RhoGEF) in the pathogenesis of amyotrophic lateral sclerosis. RGNEF is the first neurodegeneration-linked GEF that regulates not only RhoA GTPase activation but also functions as an RNA binding protein that directly acts with low molecular weight neurofilament mRNA 3' untranslated region to regulate its stability. This dual role for RGNEF, coupled with the increasing understanding of the key role for GEFs in modulating the GTPase function in cell survival suggests a prominent role for GEFs in mediating a critical balance between cytotoxicity and neuroprotection which, when disturbed, contributes to neuronal loss.

Tyrosine phosphorylation of Dbl regulates GTPase signaling

Rho GTPases are molecular "switches" that cycle between "on" (GTP-bound) and "off" (GDP-bound) states and regulate numerous cellular activities such as gene expression, protein synthesis, cytoskeletal rearrangements, and metabolic responses. Dysregulation of GTPases is a key feature of many diseases, especially cancers. Guanine nucleotide exchange factors (GEFs) of the Dbl family are activated by mitogenic cell surface receptors and activate the Rho family GTPases Cdc42, Rac1, and RhoA. The molecular mechanisms that regulate GEFs from the Dbl family are poorly understood. Our studies reveal that Dbl is phosphorylated on tyrosine residues upon stimulation by growth factors and that this event is critical for the regulated activation of the GEF. These findings uncover a novel layer of complexity in the physiological regulation of this protein.

Nonenzymatic domains of Kalirin7 contribute to spine morphogenesis through interactions with phosphoinositides and Abl

Like several Rho GDP/GTP exchange factors (GEFs), Kalirin7 (Kal7) contains an N-terminal Sec14 domain and multiple spectrin repeats. A natural splice variant of Kalrn lacking the Sec14 domain and four spectrin repeats is unable to increase spine formation; our goal was to understand the function of the Sec14 and spectrin repeat domains. Kal7 lacking its Sec14 domain still increased spine formation, but the spines were short. Strikingly, Kal7 truncation mutants containing only the Sec14 domain and several spectrin repeats increased spine formation. The Sec14 domain bound phosphoinositides, a minor but crucial component of cellular membranes, and binding was increased by a phosphomimetic mutation. Expression of KalSec14-GFP in nonneuronal cells impaired receptor-mediated endocytosis, linking Kal7 to membrane trafficking. Consistent with genetic studies placing Abl, a non-receptor tyrosine kinase, and the Drosophila orthologue of Kalrn into the same signaling pathway, Abl1 phosphorylated two sites in the fourth spectrin repeat of Kalirin, increasing its sensitivity to calpain-mediated degradation. Treating cortical neurons of the wild-type mouse, but not the Kal7(KO) mouse, with an Abl inhibitor caused an increase in linear spine density. Phosphorylation of multiple sites in the N-terminal Sec14/spectrin region of Kal7 may allow coordination of the many signaling pathways contributing to spine morphogenesis.

[Clinical features and MRI findings in spinocerebellar ataxia type 31 (SCA31) comparing with spinocerebellar ataxia type 6 (SCA6)]

Since the discovery of spinocerebellar ataxia type 31 (SCA31) gene, we identified 6 patients whose SCA type had been unkown for a long period of time as having SCA31 in our hospital and realized that SCA31 is not a rare type of autosomal dominant spinocerebellar ataxia in this region. We examined and compared the clinical details of these six SCA31 patients and the same number of SCA6 patients, finding that some SCA31 patients had hearing loss in common while there are more wide range and complicated signs of extra cerebellum in SCA6 such as pyramidal signs, extrapyramidal signs, dizzy sensations or psychotic, mental problems. There is a significant difference in the number of extracerebellar symptoms between SCA31 and SCA6. There are differences also in MRI findings. Cerebellar atrophy starts from the upper vermis in SCA31, as well as some SCA types, whereas the 4th ventricule becomes enlarged in SCA6 even in the early stage of disease. We suggest that these differences in clinical and MRI findings can be clues for accurate diagnosis before gene analysis.

Plekhg4 is a novel Dbl family guanine nucleotide exchange factor protein for rho family GTPases

Mutations in the PLEKHG4 (puratrophin-1) gene are associated with the heritable neurological disorder autosomal dominant spinocerebellar ataxia. However, the biochemical functions of this gene product have not been described. We report here that expression of Plekhg4 in the murine brain is developmentally regulated, with pronounced expression in the newborn midbrain and brainstem that wanes with age and maximal expression in the cerebellar Purkinje neurons in adulthood. We show that Plekhg4 is subject to ubiquitination and proteasomal degradation, and its steady-state expression levels are regulated by the chaperones Hsc70 and Hsp90 and by the ubiquitin ligase CHIP. On the functional level, we demonstrate that Plekhg4 functions as a bona fide guanine nucleotide exchange factor (GEF) that facilitates activation of the small GTPases Rac1, Cdc42, and RhoA. Overexpression of Plekhg4 in NIH3T3 cells induces rearrangements of the actin cytoskeleton, specifically enhanced formation of lamellopodia and fillopodia. These findings indicate that Plekhg4 is an aggregation-prone member of the Dbl family GEFs and that regulation of GTPase signaling is critical for proper cerebellar function.

Autosomal dominant cerebellar ataxia type III: a review of the phenotypic and genotypic characteristics

Autosomal Dominant Cerebellar Ataxia (ADCA) Type III is a type of spinocerebellar ataxia (SCA) classically characterized by pure cerebellar ataxia and occasionally by non-cerebellar signs such as pyramidal signs, ophthalmoplegia, and tremor. The onset of symptoms typically occurs in adulthood; however, a minority of patients develop clinical features in adolescence. The incidence of ADCA Type III is unknown. ADCA Type III consists of six subtypes, SCA5, SCA6, SCA11, SCA26, SCA30, and SCA31. The subtype SCA6 is the most common. These subtypes are associated with four causative genes and two loci. The severity of symptoms and age of onset can vary between each SCA subtype and even between families with the same subtype. SCA5 and SCA11 are caused by specific gene mutations such as missense, inframe deletions, and frameshift insertions or deletions. SCA6 is caused by trinucleotide CAG repeat expansions encoding large uninterrupted glutamine tracts. SCA31 is caused by repeat expansions that fall outside of the protein-coding region of the disease gene. Currently, there are no specific gene mutations associated with SCA26 or SCA30, though there is a confirmed locus for each subtype. This disease is mainly diagnosed via genetic testing; however, differential diagnoses include pure cerebellar ataxia and non-cerebellar features in addition to ataxia. Although not fatal, ADCA Type III may cause dysphagia and falls, which reduce the quality of life of the patients and may in turn shorten the lifespan. The therapy for ADCA Type III is supportive and includes occupational and speech modalities. There is no cure for ADCA Type III, but a number of recent studies have highlighted novel therapies, which bring hope for future curative treatments.

Cellular strategies for regulating functional and nonfunctional protein aggregation

Growing evidence suggests that aggregation-prone proteins are both harmful and functional for a cell. How do cellular systems balance the detrimental and beneficial effect of protein aggregation? We reveal that aggregation-prone proteins are subject to differential transcriptional, translational, and degradation control compared to nonaggregation-prone proteins, which leads to their decreased synthesis, low abundance, and high turnover. Genetic modulators that enhance the aggregation phenotype are enriched in genes that influence expression homeostasis. Moreover, genes encoding aggregation-prone proteins are more likely to be harmful when overexpressed. The trends are evolutionarily conserved and suggest a strategy whereby cellular mechanisms specifically modulate the availability of aggregation-prone proteins to (1) keep concentrations below the critical ones required for aggregation and (2) shift the equilibrium between the monomeric and oligomeric/aggregate form, as explained by Le Chatelier’s principle. This strategy may prevent formation of undesirable aggregates and keep functional assemblies/aggregates under control.

The spinocerebellar ataxias: clinical aspects and molecular genetics

Spinocerebellar ataxias (SCAs) are a highly heterogeneous group of inherited neurological disorders, based on clinical characterization alone with variable degrees of cerebellar ataxia often accompanied by additional cerebellar and noncerebellar symptoms which in most cases defy differentiation. Molecular causative deficits in at least 31 genes underlie the clinical symptoms in the SCAs by triggering cerebellar and, very frequently, brain stem dysfunction. The identification of the causative molecular deficits enables the molecular diagnosis of the different SCA subtypes and facilitates genetic counselling. Recent scientific advances are shedding light into developing therapeutic strategies. The scope of this chapter is to provide updated details of the spinocerebellar ataxias with particular emphasis on those aspects aimed at facilitating the clinical and genetic diagnoses.

Spinocerebellar ataxia type 31 exists in northeast China

Spinocerebellar ataxia type 31 (SCA31), is a recently defined subtype of autosomal dominant cerebellar ataxia (ADCA) characterized by late-onset pure cerebellar ataxia. SCA31 is common in Japan but whether or not it exists in other countries is still unclear. In this study, the authors describe a sporadic Chinese patient with SCA31. Although the cardinal clinical features, i.e., late-onset cerebellar ataxia and hearing impairment in our sporadic patient were similar to those described previously in Japan, mild axonal sensorimotor neuropathy was identified in our SCA31 patient, which is somewhat distinct from most prior reports of the disease. This is the first report of SCA31 in China; thus, extending the ethnic association beyond families of Japanese origin. In addition, our study suggests that the clinical features of SCA31 might be broader than previously thought.

Protein interacting with C kinase (PICK1) is a suppressor of spinocerebellar ataxia 3-associated neurodegeneration in Drosophila

Spinocerebellar ataxia 3 (SCA3) is the most common autosomal dominant ataxia. The disease is caused by an expansion of a CAG-trinucelotide repeat region within the coding sequence of the ATXN3 gene, and this results in an expanded polyglutamine (polyQ) tract within the Ataxin-3 protein. The polyQ expansion leads to neuronal dysfunction and cell death. Here, we tested the ability of a number of proteins that interact with Ataxin-3 to modulate SCA3 pathogenicity using Drosophila. Of 10 candidates, we found four novel enhancers and one suppressor. The suppressor, PICK1 (Protein interacting with C kinase 1), is a transport protein that regulates the trafficking of ion channel subunits involved in calcium homeostasis to and from the plasma membrane. In line with calcium homeostasis being a potential pathway mis-regulated in SCA3, we also found that down-regulation of Nach, an acid sensing ion channel, mitigates SCA3 pathogenesis in flies. Modulation of PICK1 could be targeted in other neurodegenerative diseases, as the toxicity of SCA1 and tau was also suppressed when PICK1 was down-regulated. These findings indicate that interaction proteins may define a rich source of modifier pathways to target in disease situations.

Spinocerebellar ataxia type 28

We have recently mapped the spinocerebellar ataxia type 28 (SCA28) locus on chromosome 18p11.22 in a four-generation Italian family. The clinical phenotype in affected individuals of this family was characterized by juvenile onset, slowly progressive gait and limb ataxia, dysarthria, hyperreflexia at lower limbs, nystagmus, and ophthalmoparesis. The mean age at onset was 19.5 years, and no evidence of anticipation between generations was observed. The disease locus on chromosome 18p11.22-q11.2 was found to span a region of 7.9 Mb of genomic DNA. Direct sequencing of candidate genes within the critical interval led to the identification of a heterozygous point mutation in one of them. The mutation was located in a highly conserved domain with proposed functional properties in the protein product of the SCA28 gene, and segregated with the disease phenotype in all affected members of this family. Further genetic screening in 105 patients with autosomal dominant spinocerebellar ataxia negative for mutations in known SCA genes allowed the identification of a distinct missense mutation in a second Italian family. Both mutations are associated with amino acid changes in evolutionarily conserved residues of the alleged SCA28 gene, and indicate SCA28 as the sixth recognized SCA genotype caused by point mutations.

[Dissecting molecular mechanism of spinocerebellar ataxia type 31]

Spinocerebellar ataxia is a group of neurodegenerative disorders clinically presenting adult onset cerebellar ataxia. To date, 21 different genes (SCA1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13, 14, 15, 17, 23, 27, 28, 31, 35, 36 and DRPLA) and additionally 10 different gene loci (SCA4, 18, 19, 20, 21, 25, 26, 29, 30 and 32) are identified. Among these, SCA6 and SCA31 are the two common diseases clinically presenting as a relatively predominant cerebellar syndrome, whereas Machado-Joseph disease/SCA3, DRPLA, SCA1 and SCA2 are SCAs often associated with extra-cerebellar manifestations. SCA31 is a late-onset purely cerebellar ataxia caused by a complex pentanucleotide repeat containing (TGGAA)(n) lying in an intronic region shared by two genes, BEAN (brain expressed, associated with NEDD4) and TK2 (thymidine kinase 2). In situ hybridization analysis in patients' Purkinje cells demonstrated that pentanucleotide repeats transcribed in BEAN direction form RNA aggregates ("RNA foci"), and essential splicing factors, SFRS1 and SFRS9, bind to (UGGAA)(n), the transcript of (TGGAA)(n)in vitro. Our preliminary data also demonstrated that (UGGAA)(n) is toxic when expressed in cultured cells. These findings may imply that RNA-mediated pathogenesis is involved in SCA31. Further studies are needed to explore precise mechanism of this disease.

[Spinocerebellar ataxia type 31]

Spinocerebellar ataxia type 31 (SCA31) is a relatively common degenerative ataxia in Japan. We recently discovered SCA31 mutation as a complex pentanucleotide repeat containing (TAAAA)(n), (TAGAA)(n), and (TGGAA)(n). The size of this repeat ranged from 2.8 to 3.5 kilo-base pairs (kb). Among these repeats, (TGGAA)(n) repeat appears crucial for SCA31 pathogenesis. The length of this complex repeat inversely correlated with ages of onset in patients. The mutation lies in an intron shared by two different genes, BEAN (brain expressed, associated with NEDD4) and TK2 (thymidine kinase 2), which are transcribed in opposite directions. Thus, the complex pentanucleotide sequence is predicted to be transcribed in both directions, but not necessarily translated into proteins. In situ hybridization analysis in patients' Purkinje cells demonstrated that pentanucleotide repeats transcribed in BEAN direction form RNA aggregates ("RNA foci"). We further found that splicing factors, SFRS1 and SFRS9, binds to (UGGAA)(n), the transcript of (TGGAA)(n) in vitro. These findings may imply that SCA31 conforms to pathogenic mechanisms underlying non-coding repeat disorders, such as myotonic dystrophies (DM1 & DM2), and that SFRS1 and SFRS9 are involved in SCA31 pathogenesis.

High frequency of submicroscopic chromosomal deletions in patients with idiopathic congenital eye malformations

PURPOSE

The purpose of this study was to evaluate the clinical usefulness of the array comparative genomic hybridization technique for the genetic analysis of patients with congenital ocular malformations.

DESIGN

Laboratory investigation.

METHODS

This was a multicenter study. Samples were collected from 37 patients with negative results for the routine diagnostic work-up, including normal karyotype and mutation analysis of appropriate genes. Samples from both parents also were tested. High-resolution genome-wide Agilent 244K oligoarray (Agilent Technologies) was applied. Confirmation of the results was obtained with independent techniques.

RESULTS

Causal deletions were identified in 5 (13%) patients, affecting OTX2, FOXC1 and VPS13B (COH1), the downstream regulatory region of PAX6, and a 1,5 Megabases de novo deletion on chromosome 16.

CONCLUSIONS

This high frequency of causal submicroscopic chromosomal aberrations in patients with congenital ocular malformation warrants implementation of array comparative genomic hybridization in the diagnostic work-up of these patients. Moreover, this screening technique broadens the phenotypic and mutational spectrum associated with genes known to cause congenital ocular malformation.

Autosomal dominant cerebellar ataxias

Cerebellar ataxias with autosomal dominant transmission (ADCA) are far rarer than sporadic cases of cerebellar ataxia. The identification of genes involved in dominant forms has confirmed the genetic heterogeneity of these conditions and of the underlying mechanisms and pathways. To date, at least 28 genetic loci and, among them, 20 genes have been identified. In many instances, the phenotype is not restricted to cerebellar dysfunction but includes more complex multisystemic neurological deficits. Seven ADCA (SCA1, 2, 3, 6, 7, 17, and dentatorubro-pallido-luysian atrophy) are caused by repeat expansions in the corresponding proteins; phenotype-genotype correlations have shown that repeat size influences the progression of the disease, its severity and clinical differences among patients, including the phenomenon of anticipation between generations. All other ADCA are caused either by non-coding repeat expansions, conventional mutations or large rearrangements in genes with different functions. This review will focus on the genetic features of ADCA and on the clinical differences among the different forms.

A de novo 1.5 Mb microdeletion on chromosome 14q23.2-23.3 in a patient with autism and spherocytosis

Autism is a neuro-developmental disorder characterized by deficits in social interaction and communication as well as restricted interests or repetitive behaviors. Cytogenetic studies have implicated large chromosomal aberrations in the etiology of approximately 5-7% of autism patients, and the recent advent of array-based techniques allows the exploration of submicroscopic copy number variations (CNVs). We genotyped a 14-year-old boy with autism, spherocytosis and other physical dysmorphia, his parents, and two non-autistic siblings with the Illumina Human 1M Beadchip as part of a study of the molecular genetics of autism and determined copy number variants using the PennCNV algorithm. We identified and validated a de novo 1.5 Mb microdeletion of 14q23.2-23.3 in our autistic patient. This region contains 15 genes, including spectrin beta (SPTB), encoding a cytoskeletal protein previously associated with spherocytosis, methylenetetrahydrofolate dehydrogenase 1 (MTHFD1), a folate metabolizing enzyme previously associated with bipoloar disorder and schizophrenia, pleckstrin homology domain-containing family G member 3 (PLEKHG3), a guanide nucleotide exchange enriched in the brain, and churchill domain containing protein 1 (CHURC1), homologs of which regulate neuronal development in model organisms. While a similar deletion has previously been reported in a family with spherocytosis, severe learning disabilities, and mild mental retardation, this is the first implication of chr14q23.2-23.3 in the etiology of autism and points to MTHFD1, PLEKHG3, and CHURC1 as potential candidate genes contributing to autism risk.

A clinically complex form of dominant optic atrophy (OPA8) maps on chromosome 16

Dominant optic atrophy (DOA) is genetically heterogeneous and pathogenic mutations have been identified in the OPA1 and OPA3 genes, both encoding for mitochondrial proteins. We characterized clinical and laboratory features in a large OPA1-negative family with complicated DOA. Search for mitochondrial dysfunction was performed by studying muscle biopsies, fibroblasts, platelets and magnetic resonance (MR) spectroscopy. Genetic investigations included mitochondrial DNA (mtDNA) analysis, linkage analysis, copy number variation (CNV) analysis and candidate gene screening. Optic neuropathy was undistinguishable from that in OPA1-DOA and frequently associated with late-onset sensorineural hearing loss, increases of central conduction times at somato-sensory evoked potentials and various cardiac abnormalities. Serum lactic acid after exercise, platelet respiratory complex activities, adenosine triphosphate (ATP) content in fibroblasts and muscle phosphorus MR spectroscopy all failed to reveal a mitochondrial dysfunction. However, muscle biopsies and their mtDNA analysis showed increased mitochondrial biogenesis. Furthermore, patient's fibroblasts grown in the galactose medium were unable to increase ATP content compared with controls, and exhibited abnormally high rate of fusion activity. Genome-wide linkage revealed a locus on chromosome 16q21-q22 with a maximum two-point LOD score of 8.84 for the marker D16S752 and a non-recombinant interval of ∼ 6.96 cM. Genomic screening of 45 genes in this interval including several likely candidate genes (CALB2, CYB5B, TK2, DHODH, PLEKHG4) revealed no mutation. Moreover, we excluded the presence of CNVs using array-based comparative genome hybridization. The identification of a new OPA locus (OPA8) in this pedigree demonstrates further genetic heterogeneity in DOA, and our results indicate that the pathogenesis may still involve mitochondria.

Analysis of an insertion mutation in a cohort of 94 patients with spinocerebellar ataxia type 31 from Nagano, Japan

Spinocerebellar ataxia type 31 (SCA31) is a recently defined subtype of autosomal dominant cerebellar ataxia (ADCA) characterized by adult-onset, pure cerebellar ataxia. The C/T substitution in the 5′-untranslated region of the puratrophin-1 gene (PLEKHG4) or a disease-specific haplotype within the 900-kb SCA31 critical region just upstream of PLEKHG4 has been used for the diagnosis of SCA31. Very recently, a disease-specific insertion containing penta-nucleotide (TGGAA)_n repeats has been found in this critical region in SCA31 patients. SCA31 was highly prevalent in Nagano, Japan, where SCA31 accounts for approximately 42% of ADCA families. We screened the insertion in 94 SCA31 patients from 71 families in Nagano. All patients had a 2.6- to 3.7-kb insertion. The size of the insertion was inversely correlated with the age at onset but not associated with the progression rate after onset. (TAGAA)_n repeats at the 5′-end of the insertion were variable in number, ranging from 0 (without TAGAA sequence) to 4. The number of (TAGAA)_n repeats was inversely correlated to the total size of the insertion. The number of (TAGAA)_n repeats was comparatively uniform within patients from the three endemic foci in Nagano. Only one patient, heterozygous for the C/T substitution in PLEKHG4, had the insertions in both alleles; they were approximately 3.0 and 4.3 kb in size. Sequencing and Southern hybridization using biotin-labeled (TGGAA)₅ probe strongly indicated that the 3.0-kb insertion, but not the 4.3-kb insertion, contained (TGGAA)_n stretch. We also found that 3 of 405 control individuals (0.7%) had the insertions from 1.0 to 3.5 kb in length. They were negative for the C/T substitution in PLEKHG4, and neither of the insertions contained (TGGAA)_n stretch at their 5′-end by sequencing. The insertions in normal controls were clearly detected by Southern hybridization using (TAAAA)₅ probe, while they were not labeled with (TGGAA)₅ or (TAGAA)₅ probe. These data indicate that control alleles very rarely have a nonpathogenic large insertion in the SCA31 critical region and that not only the presence of the insertion but also its size is not sufficient evidence for a disease-causing allele. We approve of the view that (TGGAA)_n repeats in the insertion are indeed related to the pathogenesis of SCA31, but it remains undetermined whether a large insertion lacking (TGGAA)_n is nonpathogenic.

Strategies towards high-quality binary protein interactome maps

Many processes in a cell depend on protein-protein interactions (PPIs) and perturbations of these interactions can lead to diseases. Comprehensive knowledge of PPI networks will not only give us information on how the cell is organized, but will also provide new drug targets. Current binary PPI networks are mainly generated by high-throughput yeast two-hybrid. Due to the small overlap of these maps, it has long been assumed that these maps are of low quality containing many false positives. However, by using an orthogonal two-hybrid method, MAPPIT (mammalian protein-protein interaction trap), these maps were shown to be of high quality suggesting that the limited overlap is likely due to low sensitivity and not to low specificity.

Prevalence of autosomal dominant cerebellar ataxia in Aomori, the northernmost prefecture of Honshu, Japan

OBJECTIVE

The frequency of autosomal dominant cerebellar ataxia (ADCA) varies between different regions of Japan. This is the first report on the prevalence of ADCA subtypes in Aomori, Japan.

METHODS AND PATIENTS

Sixty-five familial spinocerebellar ataxia (SCA) patients and 15 sporadic SCA patients were genetically examined. For only the SCA2 patients (n = 8), the magnetic resonance imaging (MRI) data were analyzed in detail.

RESULTS

Spinocerebellar ataxia (SCA) type 6 was often observed (77.7% of cases), with SCA2 (10.6% of cases) being the next most common form. In contrast, only one of the eighty patients had SCA1. Among the 15 sporadic SCA patients, genetic mutations for SCA2, SCA6, SCA17, and SCA31 were identified, indicating that ADCAs should be considered in sporadic cases of ataxia. Furthermore, in SCA2 cases, brainstem atrophy, pontine midline linear hyperintensity, and atrophy of the frontal lobes were frequently observed using MRI.

CONCLUSION

The present data indicate that the prevalence of ADCA in Aomori differs from other prefectures in the Tohoku District. MRI findings are very similar between SCA2 and multiple system atrophy (MSA), and thus care must be taken to prevent the misdiagnosis of sporadic SCA2 as MSA.

[Molecular genetic approach to spinocerebellar ataxias]

Spinocerebellar ataxia (SCA) is a group of degenerative ataxias with autosomal dominant inheritance. The most common form of mutation that causes SCA is the expansion of trinucleotide (CAG) repeat encoding polyglutamine. These "polyglutamine disorders" are, SCA1, SCA2, Machado-Joseph disease, SCA6, SCA7, SCA17 and DRPLA. Another dynamic mutation, yet a non-coding one, has been identified as the cause of SCA8, SCA10 and SCA12. This mutation includes, trinucleotide (CAG/CTG) expansion causing SCA8 and SCA12, and pentanuclotide (ATTCT) expansion leading SCA10. In addition to these dynamic mutations, static mutations, such as missense mutations and deletions, have been identified to cause SCA5, SCA11, SCA13, SCA14, SCA15 and SCA27. Since 1992, authors have been involved in identifying the mutation (s) of autosomal dominant cerebellar ataxia with rather pure cerebellar syndrome (ADCAIII). About a half of our cohort with ADCAIII were SCA6, caused by a small CAG repeat expansion in the alpha1A-voltage-dependent calcium channel gene. Recent study in patients' brains suggested that a small polyglutamine expansion leads a portion of this channel protein to aggregate in the Purkinje cell. Another type of ADCAIII is the chromosome 16q22.1-linked ADCA. By a comprehensive positional cloning strategy, we have found a genetic change that segregate with the disease. Identifying the mutation of 16q-ADCA is imperative for understanding molecular basis of this disease.