Nicholas T. Potter

Huntington's disease–like 2 (HDL2) in North America and Japan

Huntingtons Disease–like 2 (HDL2) is a progressive, autosomal dominant, neurodegenerative disorder with marked clinical and pathological similarities to Huntingtons disease (HD). The causal mutation is a CTG/CAG expansion mutation on chromosome 16q24.3, in a variably spliced exon of junctophilin‐3. The frequency of HDL2 was determined in nine independent series of patients referred for HD testing or selected for the presence of an HD‐like phenotype in North America or Japan. The repeat length, ancestry, and age of onset of all North American HDL2 cases were determined. The results show that HDL2 is very rare, with a frequency of 0 to 15% among patients in the nine case series with an HD‐like presentation who do not have the HD mutation. HDL2 is predominantly, and perhaps exclusively, found in individuals of African ancestry. Repeat expansions ranged from 44 to 57 triplets, with length instability in maternal transmission detected in a repeat of 33 triplets. A younger age of onset is correlated with a longer repeat length (r2 = 0.29, p = 0.0098). The results further support the evidence that the repeat expansion at the chromosome 16q24.3 locus is the direct cause of HDL2 and provide preliminary guidelines for the genetic testing of patients with an HD‐like phenotype. Ann Neurol 2004

Expression and distribution of the dentatorubral-pallidoluysian atrophy gene product (atrophin-1/drplap) in neuronal and non-neuronal tissues

Utilizing an affinity-purified antiserum directed against the carboxyl terminal region of atrophin-1/drplap (residues 1170-1185), we have examined the expression and distribution of the protein in a variety of neuronal and non-neuronal tissues. Immunohistochemical analyses of gelatin-embedded sections of monkey brain demonstrated a wide-spread distribution of the protein throughout the cerebrum and cerebellum. Labeling was primarily cytoplasmic within neuronal cell bodies and dendrites. Prominently staining regions included layers II, III, V, and VI of cerebral cortex, CA1-4 of the hippocampus, caudate nucleus, putamen, globus pallidus, amygdala, thalamus, red nucleus, pons, Purkinje cells, and deep cerebellar nuclei. Immunoblot analysis of extracts of frontal cortex from a wide variety of mammalian species (human, monkey, rabbit, rat, mouse, and bovine) detected a 190 kDa band in each extract. No cross-reactive material of similar molecular weight was detected in an extract of avian (chicken) central nervous system (CNS) tissue. Furthermore, in the rat, expression of the protein was predominantly neuronal in origin as immunoblot analyses of non-neuronal tissue extracts detected little or no 190 kDa protein. Collectively these investigations suggest a ubiquitous expression of atrophin-1/drplap in mammalian CNS tissue and provide initial immunochemical data for the study of the neuroanatomic and perhaps, phylogenetic relationships between mammalian and non-mammalian forms of the protein.

Detection of trinucleotide expansion in neurodegenerative disease by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Genotyping of the dentatorubral-pallidoluysian atrophy (DRPLA) locus in six patient samples, representing four normal individuals and two DRPLA patients, was successfully obtained using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). DRPLA is a dominantly inherited neurodegenerative disorder associated with the expansion of an unstable trinucleotide (CAG) repeat. The accurate determination of repeat length utilizing MALDI supports the use of this methodology for the analysis of genes containing unstable CAG trinucleotide repeats.

Issues & opinion. Sporadic ALS and chromosome 22: Evidence for a possible neurofilament gene defect

ALS is associated with the P2 blood group phenotype. Molecular evidence now shows the gene encoding this antigen to be on the long arm of human chromosome 22 near the newly discovered gene for heavy neurofilament (NF‐H). Since an ALS‐type condition can be generated in transgenic mice expressing the human NF‐H gene, and since the gene for the CNTF‐related cytokine leukemia inhibitory factor (LIF) is located adjacent to this gene, it is hypothesized that a defect on the chromosome 22 band region q12 is involved in the pathogenesis of sporadic ALS.

Genetic Testing for Ataxia in North America

Background: The Ataxia Molecular Diagnostics Testing Group was established to generate quantitative proficiency and outcomes data regarding molecular testing for the autosomal dominant cerebellar ataxias (spinocerebellar ataxia types 1 [SCA-1] through -3, -6, and -7, and dentatorubral-pallidoluysian atrophy) in North America.

Mutation detection in an equivocal case of Friedreich’s ataxia

Compound heterozygosity at the Friedreichs ataxia locus accounts for approximately 2% of molecularly confirmed cases. Genotype-phenotype correlation in this subgroup of patients reveals a spectrum of clinical variability. This report describes the clinical and molecular findings in a 6-year-old patient with Friedreichs ataxia who carried a pathologic GAA expansion of approximately 1,000 repeats on one allele and a novel initiation codon point mutation (3G-->A) on the other.

Use of a molecular genetic approach to diagnosing the fragile X genotype

We report the direct molecular detection of the fragile X genotype in 111 individuals from 17 families with a total of 31 cases of fragile X syndrome. Comparison of our molecular data with our previous cytogenetic and linkage data from these same families indicates the effectiveness of the direct molecular analysis. We have been able to assign a genotype unambiguously in 100% of the persons tested, and in all cases the molecular data correlated with the cytogenetic or linkage findings or both. Two of the three families presented in this study represent inheritance of this gene through normal transmitting males, and the third is strongly suggestive of this mode of inheritance. Our data show that the direct molecular approach will be of great utility for confirmation of the diagnosis and for the detection of female carriers and normal transmitting males who are at high risk for having affected children or grandchildren.

You Can Build It ... But Will They Come?: The Potential "Expansion" of Testing Methodologies for Fragile X Syndrome

This Commentary highlights a brief technical report by Iwashi and colleagues (J Mol Diagn 11: JMD08–0118) that describes an enhancement to an antibody-based ELISA assay for the detection of the FMR1 protein (FMRP) in peripheral blood.