Spinocerebellar Ataxias: Phenotypic Spectrum of PolyQ versus Non-Repeat Expansion Forms.

Spinocerebellar ataxias (SCA) are most frequently due to (CAG)n (coding for polyglutamine, polyQ) expansions and, less so, to expansion of other oligonucleotide repeats (non-polyQ) or other type of variants (non-repeat expansion SCA). In this study we compared polyQ and non-repeat expansion SCA, in a cohort of patients with hereditary ataxia followed at a tertiary hospital. From a prospective study, 88 patients (51 families) with SCA were selected, 74 (40 families) of whom genetically diagnosed. Thirty-eight patients (51.4%, 19 families) were confirmed as having a polyQ (no other repeat-expansions were identified) and 36 (48.6%, 21 families) a non-repeat expansion SCA. Median age-at-onset was 39.5 [30.0-45.5] for polyQ and 7.0 years [1.00-21.50] for non-repeat expansion SCA. PolyQ SCA were associated with cerebellar onset, and non-repeat expansion forms with non-cerebellar onset. Time to diagnosis was longer for non-repeat expansion SCA. The most common polyQ SCA were Machado-Joseph disease (MJD/SCA3) (73.7%) and SCA2 (15.8%); whereas in non-repeat expansion SCA ATX-CACNA1A (14.3%), ATP1A3-related ataxia, ATX-ITPR1, ATX/HSP-KCNA2, and ATX-PRKCG (9.5% each) predominated. Disease duration (up to inclusion) was significantly higher in non-repeat expansion SCA, but the difference in SARA score was not statistically significant. Cerebellar peduncles and pons atrophy were more common in polyQ ataxias, as was axonal neuropathy. SCA had a wide range of genetic etiology, age-at-onset and presentation. Proportion of polyQ and non-repeat expansion SCA was similar; the latter had a higher genetic heterogeneity. While polyQ ataxias were typically linked to cerebellar onset in adulthood, non-repeat expansion forms associated with early onset and non-cerebellar presentations.

Machado-Joseph disease in a Sudanese family links East Africa to Portuguese families and allows reestimation of ancestral age of the Machado lineage.

Machado-Joseph disease (MJD/SCA3) is the most frequent dominant ataxia worldwide. It is caused by a (CAG)n expansion. MJD has two major ancestral backgrounds: the Machado lineage, found mainly in Portuguese families; and the Joseph lineage, present in all five continents, probably originating in Asia. MJD has been described in a few African and African-American families, but here we report the first diagnosed in Sudan to our knowledge. The proband presented with gait ataxia at age 24; followed by muscle cramps and spasticity, and dysarthria, by age 26; he was wheel-chair bound at 29 years of age. His brother had gait problems from age 20 years and, by age 21, lost the ability to run, showed dysarthria and muscle cramps. To assess the mutational origin of this family, we genotyped 30 SNPs and 7 STRs flanking the ATXN3_CAG repeat in three siblings and the non-transmitting father. We compared the MJD haplotype segregating in the family with our cohort of MJD families from diverse populations. Unlike all other known families of African origin, the Machado lineage was observed in Sudan, being shared with 86 Portuguese, 2 Spanish and 2 North-American families. The STR-based haplotype of Sudanese patients, however, was distinct, being four steps (2 STR mutations and 2 recombinations) away from the founder haplotype shared by 47 families, all of Portuguese extraction. Based on the phylogenetic network constructed with all MJD families of the Machado lineage, we estimated a common ancestry at 3211 ± 693 years ago.

Novel Machado-Joseph disease-modifying genes and pathways identified by whole-exome sequencing.

Machado-Joseph disease (MJD/SCA3) is a neurodegenerative polyglutamine disorder exhibiting a wide spectrum of phenotypes. The abnormal size of the (CAG)n at ATXN3 explains ~55% of the age at onset variance, suggesting the involvement of other factors, namely genetic modifiers, whose identification remains limited. Our aim was to find novel genetic modifiers, analyse their epistatic effects and identify disease-modifying pathways contributing to MJD variable expressivity. We performed whole-exome sequencing in a discovery sample of four age at onset concordant and four discordant first-degree relative pairs of Azorean patients, to identify candidate variants which genotypes differed for each discordant pair but were shared in each concordant pair. Variants identified by this approach were then tested in an independent multi-origin cohort of 282 MJD patients. Whole-exome sequencing identified 233 candidate variants, from which 82 variants in 53 genes were prioritized for downstream analysis. Eighteen disease-modifying pathways were identified; two of the most enriched pathways were relevant for the nervous system, namely the neuregulin signaling and the agrin interactions at neuromuscular junction. Variants at PARD3, NFKB1, CHD5, ACTG1, CFAP57, DLGAP2, ITGB1, DIDO1 and CERS4 modulate age at onset in MJD, with those identified in CFAP57, ACTG1 and DIDO1 showing consistent effects across cohorts of different geographical origins. Network analyses of the nine novel MJD modifiers highlighted several important molecular interactions, including genes/proteins previously related with MJD pathogenesis, namely between ACTG1/APOE and VCP/ITGB1. We describe novel pathways, modifiers, and their interaction partners, providing a broad molecular portrait of age at onset modulation to be further exploited as new disease-modifying targets for MJD and related diseases.

Novel KMT2B mutation causes cerebellar ataxia: Expanding the clinical phenotype.

Hereditary cerebellar ataxias comprise a heterogeneous group of neurodegenerative disorders affecting the cerebellum and/or cerebellar pathways. Next-generation sequencing techniques have contributed substantially to the expansion of ataxia-causing genes, including genes classically described in alternative phenotypes. Herein, we describe a patient with adult-onset cerebellar ataxia, minor dystonia, neuropathy, seizure and ophthalmological pathology, who bears a novel variant in KMT2B (NM_014727.2:c.3334 + 1G > A). Bioinformatic analysis suggested this variant completely abolished the splice-site at exon 8/intron 8, which was confirmed through analysis of mRNA extracted from fibroblasts. Exon 8 skipping would ultimately translate as an in-frame deletion at the protein level, corresponding to the loss of 91 aminoacids [p.(Gly1020_Asn1111del)]. So far, KMT2B disease causing variants have been described in patients with dystonia or neurodevelopmental delay, with no reports of a cerebellar predominant phenotype. Our findings highlight the possible role of KMT2B as a gene involved in hereditary cerebellar ataxias.

Congenital ataxia due to novel variant in ATP8A2.

Congenital ataxias are a heterogeneous group of disorders characterized by congenital or early-onset ataxia. Here, we describe two siblings with congenital ataxia, who acquired independent gait by age 4 years. After 16 years of follow-up they presented near normal cognition, cerebellar ataxia, mild pyramidal signs, and dystonia. On exome sequencing, a novel homozygous variant (c.1580-18C > G - intron 17) in ATP8A2 was identified. A new acceptor splice site was predicted by bioinformatics tools, and functionally characterized through a minigene assay. Minigene constructs were generated by PCR-amplification of genomic sequences surrounding the variant of interest and cloning into the pCMVdi vector. Altered splicing was evaluated by expressing these constructs in HEK293T cells. The construct with the c.1580-18C > G homozygous variant produced an aberrant transcript, leading to retention of 17 bp of intron 17, by the use of an alternative acceptor splice site, resulting in a premature stop codon by insertion of four amino acids. These results allowed us to establish this as a disease-causing variant and expand ATP8A2-related disorders to include less severe forms of congenital ataxia.

Between responsibility and desire: Accounts of reproductive decisions from those at risk for or affected by late-onset neurological diseases.

This paper explores ways in which genetic risk foregrounds forms of responsibility while dealing with reproduction. We analyzed individual and family semi-structured interviews (n = 35) with people at-risk for or affected by transthyretin-related familial amyloid polyneuropathy (TTR-FAP) and Machado-Joseph disease (MJD), which are late-onset neurological diseases. Although generally considered as rare diseases, some areas in Portugal present the world's highest frequency for MJD and TTR-FAP. Thematic analysis of the data revealed that participants drew on various - sometimes ambivalent and competing - understandings of their genetic risk and their wish to have children. Some participants perceived the avoidance of genetic risk to be responsible behavior, while, for others, responsibility entailed accepting risks because they prioritized values such as parenthood, family relationships and the value of life, above any question of genetic disease. Some participants shared accounts that were fraught with ambivalence, repentance and guilt, especially when children were born before participants knew of their own or their partner's risk. Participants' accounts also showed they make continued efforts to see themselves as responsible persons and to appear responsible in the eyes of others. We discuss findings in the context of participants' negotiation between genetic risk and their sense of responsibility toward themselves and others; we conclude that "genetic responsibility" is present not only in accounts of those who chose not to have children but also in those who make an informed decision to have at-risk children.

A genetic interaction of NRXN2 with GABRE, SYT1 and CASK in migraine patients: a case-control study.

BACKGROUND: Migraine is a multifactorial disorder that is more frequent (two to four times) in women than in men. In recent years, our research group has focused on the role of neurotransmitter release and its regulation. Neurexin (NRXN2) is one of the components of the synaptic vesicle machinery, responsible for connecting intracellular fusion proteins and synaptic vesicles. Our aim was to continue exploring the role and interaction of proteins involved in the control and promotion of neurotransmission in migraine susceptibility. METHODS: A case-control study was performed comprising 183 migraineurs (148 females and 35 males) and 265 migraine-free controls (202 females and 63 males). Tagging single nucleotide polymorphisms of NRXN2 were genotyped to assess the association between NRXN2 and migraine susceptibility. The χ2 test was used to compare allele frequencies in cases and controls and odds ratios were estimated with 95% confidence intervals. Haplotype frequencies were compared between groups. Gene-gene interactions were analysed using the Multifactor Dimensionality Reduction v2.0. RESULTS: We found a statistically significant interaction model (p = 0.009) in the female group between the genotypes CG of rs477138 (NRXN2) and CT of rs1158605 (GABRE). This interaction was validated by logistic regression, showing a significant risk effect [OR = 4.78 (95%CI: 1.76-12.97)] after a Bonferroni correction. Our data also supports a statistically significant interaction model (p = 0.011) in the female group between the GG of rs477138 in NRXN2 and, the rs2244325's GG genotype and rs2998250's CC genotype of CASK. This interaction was also validated by logistic regression, with a protective effect [OR = 0.08 (95%CI: 0.01-0.75)]. A weak interaction model was found between NRXN2-SYT1. We have not found any statistically significant allelic or haplotypic associations between NRXN2 and migraine susceptibility. CONCLUSIONS: This study unravels, for the first time, the gene-gene interactions between NRXN2, GABRE - a GABAA-receptor - and CASK, importantly it shows the synergetic effect between those genes and its relation with migraine susceptibility. These gene interactions, which may be a part of a larger network, can potentially help us in better understanding migraine aetiology and in development of new therapeutic approaches.

A Pentanucleotide ATTTC Repeat Insertion in the Non-coding Region of DAB1, Mapping to SCA37, Causes Spinocerebellar Ataxia.

Advances in human genetics in recent years have largely been driven by next-generation sequencing (NGS); however, the discovery of disease-related gene mutations has been biased toward the exome because the large and very repetitive regions that characterize the non-coding genome remain difficult to reach by that technology. For autosomal-dominant spinocerebellar ataxias (SCAs), 28 genes have been identified, but only five SCAs originate from non-coding mutations. Over half of SCA-affected families, however, remain without a genetic diagnosis. We used genome-wide linkage analysis, NGS, and repeat analysis to identify an (ATTTC)n insertion in a polymorphic ATTTT repeat in DAB1 in chromosomal region 1p32.2 as the cause of autosomal-dominant SCA; this region has been previously linked to SCA37. The non-pathogenic and pathogenic alleles have the configurations [(ATTTT)7-400] and [(ATTTT)60-79(ATTTC)31-75(ATTTT)58-90], respectively. (ATTTC)n insertions are present on a distinct haplotype and show an inverse correlation between size and age of onset. In the DAB1-oriented strand, (ATTTC)n is located in 5' UTR introns of cerebellar-specific transcripts arising mostly during human fetal brain development from the usage of alternative promoters, but it is maintained in the adult cerebellum. Overexpression of the transfected (ATTTC)58 insertion, but not (ATTTT)n, leads to abnormal nuclear RNA accumulation. Zebrafish embryos injected with RNA of the (AUUUC)58 insertion, but not (AUUUU)n, showed lethal developmental malformations. Together, these results establish an unstable repeat insertion in DAB1 as a cause of cerebellar degeneration; on the basis of the genetic and phenotypic evidence, we propose this mutation as the molecular basis for SCA37.

Large normal alleles of ATXN2 decrease age at onset in transthyretin familial amyloid polyneuropathy Val30Met patients.

OBJECTIVE: Transthyretin (TTR)-related familial amyloid polyneuropathy (FAP) is an autosomal dominant neurological disease, caused most frequently by a Val30Met (now classified as Val50Met) substitution in TTR. Age at onset (AO) ranges from 19 to 82 years, and variability exists mostly between generations. Unstable oligonucleotide repeats in various genes are the mechanism behind several neurological diseases, found also to act as modifiers for other disorders. Our aim was to investigate whether large normal repeat alleles of 10 genes had a possible modifier effect in AO in Portuguese TTR-FAP Val30Met families. METHODS: We analyzed 329 Portuguese patients from 123 families. Repeat length (at ATXN1, ATXN2, ATXN3, ATXN7, TBP, ATN1, HTT, JPH3, AR, and DMPK) was assessed by single and multiplex polymerase chain reaction, using fluorescently labeled primers, followed by capillary electrophoresis. We used a family-centered approach, and generalized estimating equations were used to account for AO correlation between family members. RESULTS: For ATXN2, the presence of at least 1 allele longer than 22 CAGs was significantly associated with an earlier onset in TTR-FAP Val30Met, decreasing mean AO by 6 years (95% confidence interval = -8.81 to -2.19, p = 0.001). No association was found for the remaining repeat loci. INTERPRETATION: Length of normal repeats at ATXN2 may modify AO in TTR-FAP Val30Met and may function as a risk factor. This can be due to the role of ATXN2 in RNA metabolism and as a modulator of various cellular processes, including mitochondrial stress. This may have relevant implications for prognosis and the follow-up of presymptomatic carriers. ANN NEUROL 2019;85:251-258.

Going Deep into Synaptic Vesicle Machinery Genes and Migraine Susceptibility - A Case-Control Association Study.

OBJECTIVE: A number of observations, including among our study population, have implicated variants in the syntaxin-1A, a component of the synaptic vesicles, in migraine susceptibility. Therefore, we hypothesize that variants in other components of the vesicle machinery are involved in migraine. BACKGROUND: Migraine is a common and complex neurologic disorder that affects approximately 15-18% of the general population. The exact cause of migraine is unknown; however, genetic studies have made possible substantial progress toward the identification of underlying molecular pathways. Neurotransmitters have been for long considered to have a key role in migraine pathophysiology; so we investigated common variants in genes involved in the synaptic vesicle machinery and their impact in migraine susceptibility. METHODS: We performed a case-control study comprising 188 unrelated patients with headache and 286 healthy controls in a population from the north of Portugal. Benefiting from the presence of linkage disequilibrium, we selected and genotyped 119 tagging single-nucleotide polymorphisms in 18 genes. RESULTS: We found significant associations between single-nucleotide variants and migraine in 7 genes, SYN1, SYN2, SNAP25, VAMP2, STXBP1, STXBP5, and UNC13A, either conferring an increased risk or protection of migraine. Due to SYN1 X-chromosomal location, we performed the statistical analysis separated by gender and, in the female group, the C allele of rs5906435 increased the risk for migraine susceptibility (P = .021; OR = 1.69; 95% CI: 1.21-2.34). In contrast, the TT genotype of the same variant emerged as a potential protective factor (P = .003; OR = 0.45; 95% CI: 0.27-0.74). The SYN2 analysis supported the rs3773364's G allele (P = .014) as a risk factor for migraine, and although not statistically significant after correction, the AG genotype (P = .006; OR = 1.86; 95% CI: 1.20-2.90) reinforced the allelic findings. Additionally, we found the SNAP25-rs363039's CT genotype (P = .001; OR = 2.14; 95% CI: 1.36-3.34), the STXBP5-rs1765028's T allele (P = .041; OR = 1.46; 95% CI: 1.13-1.90), and the UNC13B-rs7851161's TT genotype (P = .001; OR = 2.14; 95% CI: 1.36-3.34) as statistically significant risk factors for migraine liability. VAMP2-rs1150's G allele revealed a risk association to migraine, not statistically significant after correction (P = .068). Additionally, we found haplotypes in SYN1, SYN2, STXBP1, and UNC13B to be associated with migraine. CONCLUSIONS: Overall, this study provides a new insight into migraine liability, identifying possible starting points for functional studies.

Mutational mechanism for DAB1 (ATTTC)n insertion in SCA37: ATTTT repeat lengthening and nucleotide substitution.

Dynamic mutations by microsatellite instability are the molecular basis of a growing number of neuromuscular and neurodegenerative diseases. Repetitive stretches in the human genome may drive pathogenicity, either by expansion above a given threshold, or by insertion of abnormal tracts in nonpathogenic polymorphic repetitive regions, as is the case in spinocerebellar ataxia type 37 (SCA37). We have recently established that this neurodegenerative disease is caused by an (ATTTC)n insertion within an (ATTTT)n in a noncoding region of DAB1. We now investigated the mutational mechanism that originated the (ATTTC)n insertion within an ancestral (ATTTT)n . Approximately 3% of nonpathogenic (ATTTT)n alleles are interspersed by AT-rich motifs, contrarily to mutant alleles that are composed of pure (ATTTT)n and (ATTTC)n stretches. Haplotype studies in unaffected chromosomes suggested that the primary mutational mechanism, leading to the (ATTTC)n insertion, was likely one or more T>C substitutions in an (ATTTT)n pure allele of approximately 200 repeats. Then, the (ATTTC)n expanded in size, originating a deleterious allele in DAB1 that leads to SCA37. This is likely the mutational mechanism in three similar (TTTCA)n insertions responsible for familial myoclonic epilepsy. Because (ATTTT)n tracts are frequent in the human genome, many loci could be at risk for this mutational process.

Mutations in PNKP cause recessive ataxia with oculomotor apraxia type 4.

Hereditary autosomal-recessive cerebellar ataxias are a genetically and clinically heterogeneous group of disorders. We used homozygosity mapping and exome sequencing to study a cohort of nine Portuguese families who were identified during a nationwide, population-based, systematic survey as displaying a consistent phenotype of recessive ataxia with oculomotor apraxia (AOA). The integration of data from these analyses led to the identification of the same homozygous PNKP (polynucleotide kinase 3'-phosphatase) mutation, c.1123G>T (p.Gly375Trp), in three of the studied families. When analyzing this particular gene in the exome sequencing data from the remaining cohort, we identified homozygous or compound-heterozygous mutations in five other families. PNKP is a dual-function enzyme with a key role in different pathways of DNA-damage repair. Mutations in this gene have previously been associated with an autosomal-recessive syndrome characterized by microcephaly; early-onset, intractable seizures; and developmental delay (MCSZ). The finding of PNKP mutations associated with recessive AOA extends the phenotype associated with this gene and identifies a fourth locus that causes AOA. These data confirm that MCSZ and some forms of ataxia share etiological features, most likely reflecting the role of PNKP in DNA-repair mechanisms.

A repeat-primed PCR assay for pentanucleotide repeat alleles in spinocerebellar ataxia type 37.

Spinocerebellar ataxia 37 (SCA37) is caused by an (ATTTC)n insertion in a polymorphic ATTTT repeat in the non-coding region of DAB1. The non-pathogenic alleles have a configuration [(ATTTT)7-400], whereas pathogenic alleles have a complex structure of [(ATTTT)60-79(ATTTC)31-75(ATTTT)58-90]. Molecular diagnosis of SCA37 is laborious because about 7% of the pentanucleotide repeat alleles in DAB1 are larger than 30 units and, thus, fail to amplify with standard PCR conditions, resulting in apparently homoallelism or in complete lack of PCR amplification in several cases. The molecular test currently available requires long-range PCR and sequencing analysis for the detection and characterization of these large alleles. We developed a simple assay capable of rapidly detecting the presence or absence of large pentanucleotide repeat sizes. This assay is based on repeat-primed PCR followed by high-throughput capillary electrophoresis. Combining the standard PCR with RP-PCR allows completion of the diagnosis in more than 80% of individuals, minimizing the number of samples that require long-range PCR followed by Sanger sequencing analysis. This assay meets many of the requirements for pre-screening of large cohorts of affected individuals.

Family dynamics in transthyretin-related familial amyloid polyneuropathy Val30Met: Does genetic risk affect family functioning?

Adult-onset, chronic, genetic diseases like transthyretin-related familial amyloid polyneuropathy Val30Met (TTR-FAP Val30Met), have a major psychosocial impact not only on patients, but also on families. Genetic risk may therefore be an increased factor in psychosocial impact of the disease on these families' functioning. To evaluate impact of genetic risk, a study was conducted to perceive the impact of the illness on families' functioning. Groups of TTR-FAP Val30Met patients, pre-symptomatic carriers, partners and patients with multiple sclerosis (MS), a non-hereditary disease, were studied. Sample included 190 adults: 87 patients and 28 pre-symptomatic carriers for TTR-FAP Val30Met, 41 partners and 34 patients with MS. Family Adaptability and Cohesion Scale IV (FACES IV) and a social-demographic questionnaire were applied. No significant differences were observed between patients and pre-symptomatic carriers and both these and their partners regarding cohesion and flexibility. MS patients scored significantly higher in median scores for balanced scales. Satisfaction and communication levels were also lower in patients with TTR-FAP Val30Met than with MS. Family functioning was perceived as balanced by most TTR-FAP Val30Met patients and pre-symptomatic carriers. These families may be considered as mostly healthy. Difficulties in family communication should be taken into account when caring for these families.

mtDNA copy number associated with age of onset in familial amyloid polyneuropathy.

BACKGROUND: Transthyretin-related familial amyloid polyneuropathy (TTR-FAP Val30Met) shows a wide variation in age-at-onset (AO) between generations and genders, as in Portuguese families, where women display a later onset and a larger anticipation (>10 years). Mitochondrial DNA (mtDNA) copy number was assessed to clarify whether it has a modifier effect on AO variability in Portuguese patients. METHODS: The mtDNA copy number of 262 samples (175 Val30Met TTR carriers and 87 controls (proven Val30Val)) was quantified by quantitative real-time PCR. Statistical analysis was performed using IBM SPSS V.23 software. RESULTS: This study shows that Val30Met TTR carriers have a significantly higher (p<0.001) mean mtDNA copy number than controls. Furthermore, the highest mtDNA copy number mean was observed in early-onset patients (AO <40 years). Importantly, early-onset offspring showed a significant increase (p=0.002) in the mtDNA copy number, when compared with their late AO parents. CONCLUSIONS: The present findings suggest, for the first time, that mtDNA copy number may be associated with earlier events and may therefore be further explored as a potential biomarker for follow-up of TTR-FAP Val30Met carriers.

Origins and Spread of Machado-Joseph Disease Ancestral Mutations Events.

Machado-Joseph disease (MJD) is the most common autosomal dominant spinocerebellar ataxia reported worldwide, but it shows marked geographic differences in prevalence. The study of ancestral origins and spreading routes of MJD mutational events has contributed to explain such differences. During human evolution, at least two independent de novo MJD expansions occurred in distinct haplotype backgrounds: TTACAC and GTGGCA (named Joseph and Machado lineages). The most ancient Joseph lineage, probably of Asian origin, has been introduced recently in Europe, where founder effects are responsible for the high MJD prevalence, as occurs in the Portuguese/Azorean island of Flores and Northeastern mainland. The Machado lineage is geographically more restricted, with most known families in Portugal (island of São Miguel and along the Tagus valley). The hypothesis of other mutational origins has been raised, namely to explain the disease among Australian aborigines; however, a comprehensive haplotype study suggested the introduction of the Joseph lineage in that community via Asia. Also, additional SNP-based haplotypes (TTAGAC, TTGGAC and GTGCCA) were observed in other MJD families, but phylogenetic analysis with more polymorphic flanking markers did not point to independent mutational events, reinforcing the hypothesis of a very low mutation rate underlying this repeat expansion locus.

Communication of Information about Genetic Risks: Putting Families at the Center.

Genetic information is a family affair. With the expansion of genomic technologies, many new causal genes and variants have been established and the potential for molecular diagnoses increased, with implications not only for patients but also their relatives. The need for genetic counseling and intrafamilial circulation of information on genetic risks grew accordingly. Also, the amount and, particularly, the complexity of the information to convey multiplied. Sharing information about genetic risks with family members, however, has never been an easy matter and often becomes a source of personal and familial conflicts and distress. Ethical requisites generally prevent healthcare professionals from directly contacting their consultands' relatives (affected or still at risk), who often feel unsupported throughout that process. We discuss here the communication of genetic risks to family members. We first consider genomic testing as a basis for family-centered health care, as opposed to a predominant focus on the individual. We reviewed the literature on sharing genetic risk information with family members, and the associated ethical issues for professionals. Some clinical cases are presented and discussed, and key issues for meeting the needs of individuals and families are addressed. We argue that genetic information is inextricably linked to the family and that communicating about genetic risks is a process grounded within the broader milieu of family relationships and functioning. We conclude for the need for a more family-centered approach and interventions that can promote sensitive attitudes to the provision of genetic information to and within the family, as well as its inclusion in educational and training programmes for genetic healthcare professionals.

Rare Neurodegenerative Diseases: Clinical and Genetic Update.

More than 600 human disorders afflict the nervous system. Of these, neurodegenerative diseases are usually characterised by onset in late adulthood, progressive clinical course, and neuronal loss with regional specificity in the central nervous system. They include Alzheimer's disease and other less frequent dementias, brain cancer, degenerative nerve diseases, encephalitis, epilepsy, genetic brain disorders, head and brain malformations, hydrocephalus, stroke, Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis (ALS or Lou Gehrig's Disease), Huntington's disease, and Prion diseases, among others. Neurodegeneration usually affects, but is not limited to, the cerebral cortex, intracranial white matter, basal ganglia, thalamus, hypothalamus, brain stem, and cerebellum. Although the majority of neurodegenerative diseases are sporadic, Mendelian inheritance is well documented. Intriguingly, the clinical presentations and neuropathological findings in inherited neurodegenerative forms are often indistinguishable from those of sporadic cases, suggesting that converging genomic signatures and pathophysiologic mechanisms underlie both hereditary and sporadic neurodegenerative diseases. Unfortunately, effective therapies for these diseases are scarce to non-existent. In this chapter, we highlight the clinical and genetic features associated with the rare inherited forms of neurodegenerative diseases, including ataxias, multiple system atrophy, spastic paraplegias, Parkinson's disease, dementias, motor neuron diseases, and rare metabolic disorders.