Hubertus P. H. Kremer

Spinocerebellar ataxias in the Netherlands Prevalence and age at onset variance analysis

BackgroundInternational prevalence estimates of autosomal dominant cerebellar ataxias (ADCA) vary from 0.3 to 2.0 per 100,000. The prevalence of ADCA in the Netherlands is unknown. Fifteen genetic loci have been identified (SCA-1-8, SCA-10-14, SCA-16, and SCA-17) and nine of the corresponding genes have been cloned. In SCA-1, SCA2, SCA3, SCA6, SCA7, SCA-12 and SCA-17 the mutation has been shown to be an expanded CAG repeat. Previously, the length of the CAG repeat was found to account for 50 to 80% of variance in age at onset. Because of heterogeneity in encoded proteins, different pathophysiologic mechanisms leading to neurodegeneration could be involved. The relationship between CAG repeat length and age at onset would then differ accordingly. MethodBased on the results of SCA mutation analysis in the three DNA diagnostic laboratories that serve the entire Dutch population, the authors surveyed the number of families and affected individuals per SCA gene, as well as individual repeat length and age at onset. Regression analysis was applied to study the relationship between CAG repeat length and age at onset per SCA gene. The slopes of the different regression curves were compared. ResultsOn November 1, 2000, mutations were found in 145 ADCA families and 391 affected individuals were identified. The authors extrapolated a minimal prevalence of 3.0 per 100,000 (range 2.8 to 3.8/100,000). SCA3 was the most frequent mutation. CAG repeat length contributed to 52 to 76% of age at onset variance. Regression curve slopes for SCA-1, SCA2, SCA3, and SCA7 did not differ significantly. ConclusionsThe estimated minimal prevalence of ADCA in the Netherlands is 3.0 per 100,000 inhabitants. Except for SCA6, the relationship between age at onset and CAG repeat expansion does not differ significantly between SCA-1, SCA2, SCA3, and SCA7 patient groups in our population, indicating that these SCA subtypes share similar mechanisms of polyglutamine-induced neurotoxicity, despite heterogeneity in gene products.

Identification of a novel SCA14 mutation in a Dutch autosomal dominant cerebellar ataxia family

Objective: To report a Dutch family with autosomal dominant cerebellar ataxia (ADCA) based on a novel mutation in the PRKCG gene. Methods: The authors studied 13 affected members of the six-generation family. After excluding the known spinocerebellar ataxia (SCA) genes, a combination of the shared haplotype approach, linkage analysis, and genealogic investigations was used. Exons 4 and 5 of the candidate gene, PRKCG, were sequenced. Results: Affected subjects displayed a relatively uncomplicated, slowly progressive cerebellar syndrome, with a mean age at onset of 40.8 years. A focal dystonia in two subjects with an onset of disease in their early 20s suggests extrapyramidal features in early onset disease. Significant linkage to a locus on chromosome 19q was found, overlapping the SCA-14 region. Based on the recent description of three missense mutations in the PRKCG gene, located within the boundaries of the SCA-14 locus, we sequenced exons 4 and 5 of this gene and detected a novel missense mutation in exon 4, which involves a G→A transition in nucleotide 353 and results in a glycine-to-aspartic acid substitution at residue 118. Conclusion: A SCA-14-linked Dutch ADCA family with a novel missense mutation in the PRKCG gene was identified.

A Second Gene for Autosomal Dominant Mobius Syndrome Is Localized to Chromosome 10q, in a Dutch Family

Möbius syndrome (MIM 157900) consists of a congenital paresis or paralysis of the VIIth (facial) cranial nerve, frequently accompanied by dysfunction of other cranial nerves. The abducens nerve is typically affected, and often, also, the hypoglossal nerve. In addition, orofacial and limb malformations, defects of the musculoskeletal system, and mental retardation are seen in patients with Möbius syndrome. Most cases are sporadic, but familial recurrence can occur. Different modes of inheritance are suggested by different pedigrees. Genetic heterogeneity of Möbius syndrome has been suggested by cytogenetic studies and linkage analysis. Previously, we identified a locus on chromosome 3q21-22, in a large Dutch family with Möbius syndrome consisting essentially of autosomal dominant asymmetric bilateral facial paresis. Here we report linkage analysis in a second large Dutch family with autosomal dominant inherited facial paresis. After exclusion of >90% of the genome, we identified the locus on the long arm of chromosome 10 in this family, demonstrating genetic heterogeneity of this condition. The reduced penetrance suggests that at least some of the sporadic cases might be familial.

Striking anticipation in spinocerebellar ataxia type 7: the infantile phenotype

Sirs: Autosomal dominant cerebellar ataxia type II (ADCA II) is characterised clinically by progressive cerebellar ataxia and pigmentary macular degeneration [9]. Age-at-onset may be highly variable, ranging from 1 month to 76 years, with a mean age of 32 years [2, 7, 11]. ADCA type II is genetically homogeneous and caused by a pathological CAG repeat expansion in the spinocerebellar ataxia type 7 (SCA7) gene on chromosome 3 [1]. The gene encodes for the ataxin–7 protein, the function of which remains unknown [4, 6]. Pathological repeat sizes range from 37 to 306 repeats, while normal alleles contain 4 to 35 CAG units [2, 14]. The expanded CAG repeat results in an elongated polyglutamine stretch in the ataxin–7 protein. SCA7 is therefore added to the growing list of polyglutamine tract diseases, that also includes Huntington’s disease (HD) and other SCAs. In all polyglutamine expansion diseases, an inverse relationship exists between repeat length and age-at-onset, i. e. the longer the repeat, the earlier the disease begins. These disorders also feature the phenomenon of anticipation: successive generations experience an earlier age-atonset. This is largely due to expansion of the unstable repeat during meiosis. In SCA7, the expanded repeat is more unstable in paternal than in maternal transmission [3, 8]. The rarely documented infantile SCA7 phenotype, characterised by additional extraneurological manifestations and a rapidly progressive course, is associated with enormous repeat expansions on paternal disease transmission [2, 11–13]. Here we report a family in which the onset of ataxia and subsequent detection of the SCA7 mutation in the father retrospectively explained a fatal multisystem illness in two children who died young. Family report (figure 1): Proband III–3 presented with visual complaints at age 35 years, being specified as blurred vision for distant objects with clearer vision in dimmed light. An ophthalmologist diagnosed bilateral cone dystrophy. Because of consanguinity of the proband’s parents, an autosomal recessive pattern of inheritance was considered. LETTER TO THE EDITORS

Genotype-phenotype correlations in spastic paraplegia type 7 : a study in a large Dutch cohort

Spastic paraplegia type 7 is an autosomal recessive neurodegenerative disorder mainly characterized by progressive bilateral lower limb spasticity and referred to as a form of hereditary spastic paraplegia. Additional disease features may also be observed as part of a more complex phenotype. Many different mutations have already been identified, but no genotype-phenotype correlations have been found so far. From a total of almost 800 patients referred for testing, we identified 60 patients with mutations in the SPG7 gene. We identified 14 previously unreported mutations and detected a high recurrence rate of several earlier reported mutations. We were able to collect detailed clinical data for 49 patients, who were ranked based on a pure versus complex phenotype, ataxia versus no ataxia and missense versus null mutations. A generally complex phenotype occurred in 69% of all patients and was associated with a younger age at onset (trend with P = 0.07). Ataxia was observed in 57% of all patients. We found that null mutations were associated with the co-occurrence of cerebellar ataxia (trend with P = 0.06). The c.1409 G > A (p.Arg470Gln) mutation, which was found homozygously in two sibs, was associated with a specific complex phenotype that included predominant visual loss due to optical nerve atrophy. Neuropathology in one of these cases showed severe degeneration of the optic system, with less severe degeneration of the ascending tracts of the spinal cord and cerebellum. Other disease features encountered in this cohort included cervical dystonia, vertical gaze palsy, ptosis and severe intellectual disability. In this large Dutch cohort, we seem to have identified the first genotype-phenotype correlation in spastic paraplegia type 7 by observing an association between the cerebellar phenotype of spastic paraplegia type 7 and SPG7 null alleles. An overlapping phenotypic presentation with its biological counterpart AFG3L2, which when mutated causes spinocerebellar ataxia type 28, is apparent and possibly suggests that abnormal levels of the SPG7 protein impact the function of the mitochondrial ATPases associated with diverse cellular activities-protease complex (formed by SPG7 and AFG3L2) in the cerebellum. In addition, a missense mutation in exon 10 resulted in predominant optical nerve atrophy, which might suggest deleterious interactions of this SPG7 variant with its substrate OPA1, the mutated gene product in optic atrophy type 1. Functional studies are required to further investigate these interactions.

Reviewing the genetic causes of spastic-ataxias

Although the combined presence of ataxia and pyramidal features has a long differential, the presence of a true spastic-ataxia as the predominant clinical syndrome has a rather limited differential diagnosis. Autosomal recessive ataxia of Charlevoix-Saguenay, late-onset Friedreich ataxia, and hereditary spastic paraplegia type 7 are examples of genetic diseases with such a prominent spastic-ataxic syndrome as the clinical hallmark. We review the various causes of spastic-ataxic syndromes with a focus on the genetic disorders, and provide a clinical framework, based on age at onset, mode of inheritance, and additional clinical features and neuroimaging signs, that could serve the diagnostic workup.

Ataxia rating scales are age‐dependent in healthy children

To investigate ataxia rating scales in children for reliability and the effect of age and sex.

Ramsay Hunt Syndrome: Clinical Characterization of Progressive Myoclonus Ataxia Caused by GOSR2 Mutation

Ramsay Hunt syndrome (progressive myoclonus ataxia) is a descriptive diagnosis characterized by myoclonus, ataxia, and infrequent seizures. Often the etiology cannot be determined. Recently, a mutation in the GOSR2 gene (c.430G>T, p.Gly144Trp) was reported in 6 patients with childhood‐onset progressive ataxia and myoclonus.

Long-term Consequences of the Posterior Reversible Encephalopathy Syndrome in Eclampsia and Preeclampsia: A Review of the Obstetric and Nonobstetric Literature

&NA; This review summarizes the long-term consequences of the posterior reversible encephalopathy syndrome (PRES) that have been described in the obstetric literature (eclampsia and preeclampsia) and compares these with data from the nonobstetric literature. Preeclampsia is characterized by new-onset hypertension and proteinuria after the 20th week of pregnancy. Neurological symptoms include headache; visual deficits; confusion; seizures; and, in the most severe cases, intracranial hemorrhage. Eclampsia is an acute cerebral complication of preeclampsia, defined as the occurrence of tonic-clonic seizures in pregnant or recently postpartum women. With severe preeclampsia, in conjunction with neurological symptoms, or eclampsia, neuroimaging changes consistent with PRES can be seen. Posterior reversible encephalopathy syndrome is a specific clinicoradiological syndrome presenting with headaches, visual impairment, seizures, and altered mental status. Characteristic neuroimaging features are consistent with cerebral edema predominantly in the parietal and occipital lobes. In addition to preeclampsia/eclampsia, PRES has been associated with various conditions in the nonobstetric population, that is, severe hypertension, transplantation, or autoimmune disease, in combination with immunosuppressive therapy or high-dose chemotherapy for various malignant conditions. Long-term sequelae of both preeclampsia/eclampsia and other PRES-related conditions are poorly described. After eclampsia or preeclampsia, nonspecific white matter lesions may be found on magnetic resonance imaging, which may or may not be related to the PRES episode. Previously (pre)eclamptic women report cognitive failures; however, no neurocognitive impairment has been shown so far. Various nonobstetric PRES-related conditions have been described with long-term neuroimaging abnormalities as well as cognitive problems, epilepsy, or visual impairment. Although no firm conclusions can be drawn because of the heterogeneity of reported cases, some general comments can be made. Because most persistent long-term problems are present in the nonobstetric population, the main determinant for these long-term problems may be the underlying condition that gave rise to the PRES episode. In addition, most reports suggest that late diagnosis or inadequate therapy may contribute, emphasizing the need for early recognition, adequate treatment, follow-up, and support. Target Audience Obstetricians and gynecologists, neurologists, radiologists, ophthalmologists, psychologists Learning Objectives After completing this CME activity, the reader should be able to identify the clinicoradiological syndrome and pathophysiology of PRES in preeclampsia/eclampsia, evaluate long-term consequences and complaints in formerly preeclamptic and eclamptic women, and determine the need for early magnetic resonance imaging diagnosis of PRES.

A novel locus for autosomal dominant non-syndromic hearing loss, DFNA31, maps to chromosome 6p21.3.

Background:Non-syndromic hearing loss is the most genetically heterogeneous trait known in humans. To date, 51 loci for autosomal dominant non-syndromic sensorineural hearing loss (NSSHL) have been identified by linkage analysis. Objective:To investigate the genes involved in a Dutch family with NSSHL. Methods:Linkage analysis in a large Dutch pedigree with progressive bilateral loss of the mid and high frequencies, in which a novel dominant locus for postlingual NSSHL (DFNA31) has been identified. Results:DFNA31 was found to be located in a 7.5 cM region of chromosome 6p21.3 between D6S276 (telomeric) and D6S273 (centromeric), with a maximum two point LOD score of 5.99 for D6S1624. DNA sequencing of coding regions and exon/intron boundaries of two candidate genes (POU5F1, GABBR1) in this interval did not reveal disease causing mutations. Conclusions:Haplotype analysis indicated that the genetic defect in this family does not overlap the DFNA13 and DFNA21 regions that are also located on 6p. Identification of the disease gene will be of major importance in understanding the pathophysiology of hearing impairment.