Emilia Bellone

Corticobasal degeneration shares a common genetic background with progressive supranuclear palsy

Corticobasal degeneration is a sporadic form of tauopathy, involving the cerebral cortex and extrapyramidal motor system. A series of affected subjects was genotyped for a set of genetic markers along the tau protein gene. A specific haplotype is significantly overrepresented in patients versus controls. This haplotype is the same already reported in association with progressive supranuclear palsy. These data show that corticobasal degeneration and progressive supranuclear palsy, in addition to several clinical, pathological, and molecular features, may have the same genetic background. Ann Neurol 2000;47:374–377

A Novel Mutation (D305V) in the Early Growth Response 2 Gene Is Associated with Severe Charcot- Marie-Tooth Type 1 Disease

Hereditary motor and sensory neuropathies (HMSN) comprises a wide clinical spectrum of related disorders with defects in peripheral nerve myelination. Charcot‐Marie‐Tooth type 1 (CMT1) is the most common form and is usually a mild disease with onset in the first or second decade; however there is a interfamilial and intrafamilial clinical variation, ranging from asymptomatic expression to severe muscular weakness and atrophy. Recently point mutations in the early growth response 2 gene (EGR2/Krox‐20) have been associated with hereditary myelinopathies. We investigated for mutations at the EGR2 gene a patient with severe CMT1 phenotype. Direct sequencing of EGR2 gene showed a heterozygous A T transversion at nucleotide 1064 that predicts an Asp305Val substitution within the first zinc‐finger domain. The finding of a novel EGR2 mutation associated with a different phenotype confirms that peripheral neuropathies represent a continuum spectrum of related disorders due to an underlying defect in myelination. Hum Mutat 14:353–354, 1999.

Family and molecular data for a fine analysis of age at onset in Huntington disease

We analyzed the data on age at onset and CAG size of 319 patients clinically diagnosed with Huntington disease (HD) and 86 presymptomatic subjects recorded by four Italian Centers over the last 14 years. To overcome the problem of different CAG numbers found in each subject, also in the same family, the data were analyzed in terms of deviations from the average exponential relationship between onset and CAG number. The subjects year of birth was also considered to quantify possible sampling biases. Observations between relatives were compared with those of the whole group. The deviations were equal, on average, in subjects who inherited their HD gene from their fathers or mothers. Overall, our data argue in favor of a greater similarity across the same generation than across successive generations. In particular, an excess of parents with later than expected age of onset was observed, paralleled by a CAG-independent anticipation of onset in parent-child transmissions. These results can be interpreted in terms of a shared environment determining similar departures from the average CAG-onset relationship but also of a systematic effect that differentiates the two generations here examined.

Triplet Repeat Primed PCR (TP PCR) in Molecular Diagnostic Testing for Friedreich Ataxia

Friedreich ataxia (FRDA), an autosomal recessive neurodegenerative disease, is associated with an unstable expansion of a GAA trinucleotide repeat in the first intron of the frataxin gene on chromosome 9q13. Unequivocal molecular characterization of the FRDA triplet expansion requires the use of different PCR protocols to amplify normal and mutated alleles combined with Southern blotting analysis to accurately size the expansion. Nevertheless, expansion detection by PCR may be somewhat problematic in heterozygous individuals. The purpose of this study was to evaluate triplet repeat primed PCR (TP PCR) as a screening method for FRDA diagnosis in the diagnostic laboratory. Fifty-four cases referred either to confirm the diagnosis of FRDA or to detect carrier status were re-evaluated by the TP PCR method. The TP PCR assay correctly identified the FRDA status in all 54 individuals tested including homozygous expansions (9 individuals), heterozygous expansions (20 individuals), and non-carriers (25 individuals). Results showed 100% concordance with those obtained by Southern blot analysis. TP PCR allowed us to identify the expanded alleles or to demonstrate their absence in DNA samples where conventional PCR procedures failed to give a reliable result. TP PCR represents an additional valuable tool for mutation detection in FRDA patients and carriers, but also can be used as screening test in a diagnostic laboratory.

Congenital hypomyelination due to myelin protein zero Q215X mutation

Congenital hypomyelination (CH) is a hereditary demyelinating peripheral neuropathy characterized by early infancy onset, distal muscle weakness, hypotonia, areflexia, and severe slowing of nerve conduction velocities. In the present report, the clinical, morphological, and immunohistochemical features of a CH case and the identification of a mutation in the gene (MPZ) for protein zero (P0) associated with this phenotype are described. This “de novo” mutation in a patient presenting with clinical features quite distinct from those of the more frequent Charcot‐Marie‐Tooth type 1B disease (CMT1B) or Dejerine‐Sottas syndrome (DSS) confirms that CH is allelic with other disorders characterized by a less severe phenotype and a different clinical and neuropathological profile. Ann Neurol 1999;45:676–678

mRNA distribution in adult human brain of GRIN2B, a N-methyl-D-aspartate (NMDA) receptor subunit.

The expression of the N-methyl-D-aspartate (NMDA) receptor subunit NR2B/epsilon2 (GRIN2B) in the human adult brain was assayed by in situ hybridisation, by using a specific cRNA probe. The full length GRIN2B cDNA was cloned and sequenced. It showed a 90% nucleotide conservation when compared to the rodent homologue. GRIN2B gene is expressed at high levels in the fronto-parieto-temporal cortex and hippocampus pyramidal cells and, at a lower extent, in the basal ganglia (amygdala and striatum). The cerebellar granule cells does not show any mRNA expression. The non-ubiquitous anatomical distribution of the GRIN2B mRNA in the central nervous system suggests that the gene could be involved in specific functions pertaining to the expressing cell groups.

HSPB1 and HSPB8 in inherited neuropathies: study of an Italian cohort of dHMN and CMT2 patients.

Mutations in the small heat‐shock protein 27 kDa protein 1 (HSPB1) and 22 kDa protein 8 (HSPB8) genes were associated with distal hereditary motor neuropathy (dHMN) and with the axonal form of Charcot‐Marie‐Tooth disease type 2 (CMT2). Here we report the clinical and molecular evaluation of an Italian dHMN and CMT2 cohort to establish HSPB1 and HSPB8 mutation occurrence and associated clinical features. One hundred and sixty‐seven patients with dHMN or CMT2 were studied. HSPB1 and HSPB8 exons 1 and 3 molecular analysis was carried out through DHPLC and direct sequencing of each variant chromatogram. HSPB8 exon 2 was analyzed by direct sequencing. Four mutations in five unrelated dHMN patients and four mutations in four unrelated CMT2 cases were found in HSPB1. The p.Arg136Leu mutation was found in two patients with different phenotypes. Electroneurographical follow‐up study in a dHMN patient revealed that sensory impairment occurred with disease progression. The HSPB1 mutation frequency was 8% in dHMN and 4% in CMT2 patients. The significant HSPB1 mutation frequency in both phenotypes indicates its relevance in the pathogenesis of these neuropathies. Recent literature data suggest a continuum between dHMN and CMT2. We confirm this finding in our cohort, proposing a definite relationship between these disorders.

Variations in the NMDA receptor subunit 2B gene (GRIN2B) and schizophrenia: A case‐control study

A well established model for the pathophysiology of schizophrenia postulates a role for the NMDA‐mediated glutamate transmission. The human gene coding for the 2B subunit of the NMDA receptor (GRIN2B) is considered a candidate based on its selective expression in brain. To evaluate the hypothesis that GRIN2B acts as a major gene in determining susceptibility to schizophrenia, a case‐control association study was performed. Five single nucleotide polymorphisms (SNPs) were genotyped in 188 Italian patients and 156 control subjects. The association study showed a marginally significant excess of homozygosity for the polymorphism located in the 3′UTR region (P = 0.04). No other difference in genotype and allele frequencies was found in schizophrenics as compared to the control series. The case‐control study was also carried out on estimated haplotypes, confirming a trend for association (P = 0.04). These results suggest that GRIN2B variations might be linked with susceptibility to schizophrenia. Replication studies on larger samples are warranted to further test this hypothesis.

HMSN III phenotype due to homozygous expression of a dominant HMSN II gene

We describe two siblings with hereditary motor and sensory neuropathy (HMSN) type III. Their parents were both affected with autosomal dominant axonal HMSN. The neuropathy in the siblings probably resulted from homozygous expression of the HMSN II gene. Together with other reports of homozygous HMSN I, this family suggests that HMSN III is heterogenous and encompasses the most severe homozygous expression of neuropathic genes.

Enlarging clinical spectrum of FALS with TARDBP gene mutations: S393L variant in an Italian family showing phenotypic variability and relevance for genetic counselling

Objective: The present study was aimed to enlarge the Italian ALS sample analysed for TARDBP gene mutations. Methods: Genomic DNA from 47 patients, 70 FTD patients and 158 controls was extracted from peripheral blood samples according to a standard protocol. The five coding exons (2–6) of the TARDBP gene and the flanking exon-intron boundaries were analysed by direct sequencing. Using ClustalW2 human TDP-43, protein sequence was aligned with TDP-43 protein sequence of different species. Results: A heterozygous c.1178 C→T transition that leads to a change p.S393L was observed in a 75-years-old male patient and in his two affected siblings. A patients brother had died at 69 years of age after a two-year history of ALS. In FTD patients no mutations were found. Conclusions: We describe a further Italian family with FALS, in which a variant (p.S393L) of the TARDBP gene was identified. Clinical course and phenotypic variability in three affected siblings is presented and relevance for genetic counselling of patients and their families is underlined. At the present state of knowledge, we suggest that the same guidelines established for SOD1 molecular testing could be proposed also for TARDBP analysis in FALS.