Emilio Di Maria

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.

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.

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.

The D355V Mutation Decreases EGR2 Binding to an Element within the Cx32 Promoter

Mutations in the early growth response 2 (EGR2) gene are associated with some forms of Charcot--Marie--Tooth disease (CMT) and other demyelinating neuropathies. These mutations modify the EGR2 binding to specific DNA sequences suggesting a role in the transcriptional control of myelination-specific genes. Here we show that the D355V mutation, associated with a CMT case combining axonal and demyelinating abnormalities, reduces three times the affinity of EGR2 to its consensus sequence and ten times its affinity to a sequence in the human Cx32 promoter. These findings could indicate that this EGR2 mutation leads to the development of CMT1 through the transcriptional deregulation of Cx32 gene.

Does parkin play a role in the peripheral nervous system? A family report

Two genes were identified for autosomal recessive forms of early onset Parkinsons disease: parkin and DJ‐1. We describe 2 siblings with EOPD due to parkin mutations and peripheral neuropathy, which presented as neuropathy with liability to pressure palsies (HNPP) in the index case. RT‐PCR experiments revealed that the parkin gene is expressed in sural nerves from both controls and patient with parkin‐related disease. Our findings support the view that parkin may play a role in the peripheral nervous system.

The H1 haplotype of the tau gene (MAPT) is associated with mild cognitive impairment.

Mild cognitive impairment is often considered a transitional condition prodromal to Alzheimers disease. The dissection of genetic risk factors predisposing to mild cognitive impairment is paramount to assess the individual predisposition and reliably evaluate the effectiveness of early therapeutic interventions. We designed a cross-sectional analysis to test whether the occurrence of mild cognitive impairment is influenced by variations of the tau protein gene. The genotypes of seven polymorphisms tagging the major tau haplotypes were assayed on 186 patients with amnestic mild cognitive impairment and 191 unrelated controls. Association study was conducted by logistic regression including APOE genotype and age as covariates. Case-control analysis showed that the common H1 haplotype is significantly overrepresented in patients (OR, 95% CI: 2.31, 1.52-3.51; p<0.001), whereas did not provide positive signals for any of the H1 sub-haplotypes that had been described as associated with Alzheimer inverted exclamation mark s disease. This finding was confirmed when the epsilon4 allele of the APOE gene was taken into account (OR, 95% CI: 2.319, 1.492-3.603; p<0.001). These results firstly suggest that the risk of mild cognitive impairment is influenced by tau protein gene variations and that mild cognitive impairment shares a common genetic background with Alzheimers disease. They may help elucidating the genetic risk to cognitive decline and designing effective clinical trials.

The policy of public health genomics in Italy

Italy has a monitoring system for genetic testing, consisting in a periodic census of clinical and laboratory activities performed in the country. The experience is limited, however, concerning the translation of genomic testing for complex diseases into clinical practice. For the first time the Italian Ministry of Health has introduced a policy strategic plan on genomics and predictive medicine within the 2010-2012 National Prevention Plan. This achievement was supported by the Italian Network for Public Health Genomics (GENISAP) and will likely contribute to the integration of public health genomics into health care in the country. Our experience might be of interest not only in Italy, but in other high-income countries, struggling to keep a healthy economy and healthy citizens.

Genetic Variation in the G720/G30 Gene Locus (DAOA) Influences the Occurrence of Psychotic Symptoms in Patients with Alzheimer's Disease

The occurrence of neuropsychiatric symptoms in patients with Alzheimers disease hampers the clinical management and exacerbates the burden for caregivers. To what extent psychotic symptoms are genetically determined and which are the genes involved has to be established. We tested the hypothesis that the occurrence of delusions and hallucinations in AD is associated with variations in the G72/DAOA gene, which is supposed to play a key role in the glutamate pathway regulated through the NMDA receptors. A panel of single nucleotide polymorphisms were genotyped in a cohort of 185 Alzheimers disease patients. The analysis demonstrated a nominally significant association (p< 0.05) with one single nucleotide polymorphism (rs2153674). In addition, multivariate regression showed that the rs2153674 genotype accounts for up to 15% of the variance in delusions severity, as assessed by using the Neuropsychiatric Inventory. If the results from the present study will be replicated, the glutamate hypothesis could be invoked to explain the occurrence of psychosis in neurodegenerative disorders.

Essential tremor is not associated with α-synuclein gene haplotypes

A specific allele of the NACP‐Rep1 polymorphism within the α‐synuclein promoter was found to be associated both with Parkinsons disease and essential tremor. We repeated the association study on a large series of Italian patients with essential tremor using a panel of polymorphisms within the α‐synuclein gene. Our results did not confirm the association reported previously and failed to identify a α‐synuclein specific haplotype as susceptibility factor for essential tremor.