Publications by authors named "Alleene Strickland"

9 Publications

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Variant pathogenicity evaluation in the community-driven Inherited Neuropathy Variant Browser.

Hum Mutat 2018 05 14;39(5):635-642. Epub 2018 Mar 14.

Dr. John T. Macdonald Foundation Department of Human Genetics, University of Miami, Miami, Florida.

Charcot-Marie-Tooth disease (CMT) is an umbrella term for inherited neuropathies affecting an estimated one in 2,500 people. Over 120 CMT and related genes have been identified and clinical gene panels often contain more than 100 genes. Such a large genomic space will invariantly yield variants of uncertain clinical significance (VUS) in nearly any person tested. This rise in number of VUS creates major challenges for genetic counseling. Additionally, fewer individual variants in known genes are being published as the academic merit is decreasing, and most testing now happens in clinical laboratories, which typically do not correlate their variants with clinical phenotypes. For CMT, we aim to encourage and facilitate the global capture of variant data to gain a large collection of alleles in CMT genes, ideally in conjunction with phenotypic information. The Inherited Neuropathy Variant Browser provides user-friendly open access to currently reported variation in CMT genes. Geneticists, physicians, and genetic counselors can enter variants detected by clinical tests or in research studies in addition to genetic variation gathered from published literature, which are then submitted to ClinVar biannually. Active participation of the broader CMT community will provide an advance over existing resources for interpretation of CMT genetic variation.
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http://dx.doi.org/10.1002/humu.23412DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5903998PMC
May 2018

Characterizing the molecular phenotype of an Atp7a(T985I) conditional knock in mouse model for X-linked distal hereditary motor neuropathy (dHMNX).

Metallomics 2016 09 13;8(9):981-92. Epub 2016 Jun 13.

Northcott Neuroscience Laboratory, ANZAC Research Institute, Concord, NSW, Australia.

ATP7A is a P-type ATPase essential for cellular copper (Cu) transport and homeostasis. Loss-of-function ATP7A mutations causing systemic Cu deficiency are associated with severe Menkes disease or its milder allelic variant, occipital horn syndrome. We previously identified two rare ATP7A missense mutations (P1386S and T994I) leading to a non-fatal form of motor neuron disorder, X-linked distal hereditary motor neuropathy (dHMNX), without overt signs of systemic Cu deficiency. Recent investigations using a tissue specific Atp7a knock out model have demonstrated that Cu plays an essential role in motor neuron maintenance and function, however the underlying pathogenic mechanisms of ATP7A mutations causing axonal degeneration remain unknown. We have generated an Atp7a conditional knock in mouse model of dHMNX expressing Atp7a(T985I), the orthologue of the human ATP7A(T994I) identified in dHMNX patients. Although a degenerative motor phenotype is not observed, the knock in Atp7a(T985I/Y) mice show altered Cu levels within the peripheral and central nervous systems, an increased diameter of the muscle fibres and altered myogenin and myostatin gene expression. Atp7a(T985I/Y) mice have reduced Atp7a protein levels and recapitulate the defective trafficking and altered post-translational regulatory mechanisms observed in the human ATP7A(T994I) patient fibroblasts. Our model provides a unique opportunity to characterise the molecular phenotype of dHMNX and the time course of cellular events leading to the process of axonal degeneration in this disease.
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http://dx.doi.org/10.1039/c6mt00082gDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5586149PMC
September 2016

De novo PMP2 mutations in families with type 1 Charcot-Marie-Tooth disease.

Brain 2016 06 23;139(Pt 6):1649-56. Epub 2016 Mar 23.

Department of Neurology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA

We performed whole exome sequencing on a patient with Charcot-Marie-Tooth disease type 1 and identified a de novo mutation in PMP2, the gene that encodes the myelin P2 protein. This mutation (p.Ile52Thr) was passed from the proband to his one affected son, and segregates with clinical and electrophysiological evidence of demyelinating neuropathy. We then screened a cohort of 136 European probands with uncharacterized genetic cause of Charcot-Marie-Tooth disease and identified another family with Charcot-Marie-Tooth disease type 1 that has a mutation affecting an adjacent amino acid (p.Thr51Pro), which segregates with disease. Our genetic and clinical findings in these kindred demonstrate that dominant PMP2 mutations cause Charcot-Marie-Tooth disease type 1.
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http://dx.doi.org/10.1093/brain/aww055DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5022672PMC
June 2016

Mutations in SLC25A46, encoding a UGO1-like protein, cause an optic atrophy spectrum disorder.

Nat Genet 2015 Aug 13;47(8):926-32. Epub 2015 Jul 13.

Department of Biology, University of Miami, Coral Gables, Florida, USA.

Dominant optic atrophy (DOA) and axonal peripheral neuropathy (Charcot-Marie-Tooth type 2, or CMT2) are hereditary neurodegenerative disorders most commonly caused by mutations in the canonical mitochondrial fusion genes OPA1 and MFN2, respectively. In yeast, homologs of OPA1 (Mgm1) and MFN2 (Fzo1) work in concert with Ugo1, for which no human equivalent has been identified thus far. By whole-exome sequencing of patients with optic atrophy and CMT2, we identified four families with recessive mutations in SLC25A46. We demonstrate that SLC25A46, like Ugo1, is a modified carrier protein that has been recruited to the outer mitochondrial membrane and interacts with the inner membrane remodeling protein mitofilin (Fcj1). Loss of function in cultured cells and in zebrafish unexpectedly leads to increased mitochondrial connectivity, while severely affecting the development and maintenance of neurons in the fish. The discovery of SLC25A46 strengthens the genetic overlap between optic atrophy and CMT2 while exemplifying a new class of modified solute transporters linked to mitochondrial dynamics.
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http://dx.doi.org/10.1038/ng.3354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4520737PMC
August 2015

Mutation screen reveals novel variants and expands the phenotypes associated with DYNC1H1.

J Neurol 2015 Sep 24;262(9):2124-34. Epub 2015 Jun 24.

Department of Orthopaedics, Medical University Vienna, Währingergürtel 18-20, 1090, Vienna, Austria.

Dynein, cytoplasmic 1, heavy chain 1 (DYNC1H1) encodes a necessary subunit of the cytoplasmic dynein complex, which traffics cargo along microtubules. Dominant DYNC1H1 mutations are implicated in neural diseases, including spinal muscular atrophy with lower extremity dominance (SMA-LED), intellectual disability with neuronal migration defects, malformations of cortical development, and Charcot-Marie-Tooth disease, type 2O. We hypothesized that additional variants could be found in these and novel motoneuron and related diseases. Therefore, we analyzed our database of 1024 whole exome sequencing samples of motoneuron and related diseases for novel single nucleotide variations. We filtered these results for significant variants, which were further screened using segregation analysis in available family members. Analysis revealed six novel, rare, and highly conserved variants. Three of these are likely pathogenic and encompass a broad phenotypic spectrum with distinct disease clusters. Our findings suggest that DYNC1H1 variants can cause not only lower, but also upper motor neuron disease. It thus adds DYNC1H1 to the growing list of spastic paraplegia related genes in microtubule-dependent motor protein pathways.
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http://dx.doi.org/10.1007/s00415-015-7727-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4573829PMC
September 2015

A novel mutation in VCP causes Charcot-Marie-Tooth Type 2 disease.

Brain 2014 Nov 14;137(Pt 11):2897-902. Epub 2014 Aug 14.

2 Department of Neurology, University of Iowa, 200 Hawkins Drive, Iowa City, IA 52242, USA

Mutations in VCP have been reported to account for a spectrum of phenotypes that include inclusion body myopathy with Paget's disease of the bone and frontotemporal dementia, hereditary spastic paraplegia, and 1-2% of familial amyotrophic lateral sclerosis. We identified a novel VCP mutation (p.Glu185Lys) segregating in an autosomal dominant Charcot-Marie-Tooth disease type 2 family. Functional studies showed that the Glu185Lys variant impaired autophagic function leading to the accumulation of immature autophagosomes. VCP mutations should thus be considered for genetically undefined Charcot-Marie-Tooth disease type 2.
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http://dx.doi.org/10.1093/brain/awu224DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4208462PMC
November 2014

Characterization of the mitofusin 2 R94W mutation in a knock-in mouse model.

J Peripher Nerv Syst 2014 Jun;19(2):152-64

Department of Human Genetics, Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Miami, FL, USA.

Charcot-Marie-Tooth disease (CMT) comprises a group of heterogeneous peripheral axonopathies affecting 1 in 2,500 individuals. As mutations in several genes cause axonal degeneration in CMT type 2, mutations in mitofusin 2 (MFN2) account for approximately 90% of the most severe cases, making it the most common cause of inherited peripheral axonal degeneration. MFN2 is an integral mitochondrial outer membrane protein that plays a major role in mitochondrial fusion and motility; yet the mechanism by which dominant mutations in this protein lead to neurodegeneration is still not fully understood. Furthermore, future pre-clinical drug trials will be in need of validated rodent models. We have generated a Mfn2 knock-in mouse model expressing Mfn2(R94W), which was originally identified in CMT patients. We have performed behavioral, morphological, and biochemical studies to investigate the consequences of this mutation. Homozygous inheritance leads to premature death at P1, as well as mitochondrial dysfunction, including increased mitochondrial fragmentation in mouse embryonic fibroblasts and decreased ATP levels in newborn brains. Mfn2(R94W) heterozygous mice show histopathology and age-dependent open-field test abnormalities, which support a mild peripheral neuropathy. Although behavior does not mimic the severity of the human disease phenotype, this mouse can provide useful tissues for studying molecular pathways associated with MFN2 point mutations.
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http://dx.doi.org/10.1111/jns5.12066DOI Listing
June 2014

Genetics of Charcot-Marie-Tooth (CMT) Disease within the Frame of the Human Genome Project Success.

Genes (Basel) 2014 Jan 22;5(1):13-32. Epub 2014 Jan 22.

Department of Human Genetics, Hussman Institute for Human Genomics, University of Miami Miller School of Medicine, Biomedical Research Building, Room 523, LC: M-860, 1501 NW 10 Ave., Miami, FL 33136, USA.

Charcot-Marie-Tooth (CMT) neuropathies comprise a group of monogenic disorders affecting the peripheral nervous system. CMT is characterized by a clinically and genetically heterogeneous group of neuropathies, involving all types of Mendelian inheritance patterns. Over 1,000 different mutations have been discovered in 80 disease-associated genes. Genetic research of CMT has pioneered the discovery of genomic disorders and aided in understanding the effects of copy number variation and the mechanisms of genomic rearrangements. CMT genetic study also unraveled common pathomechanisms for peripheral nerve degeneration, elucidated gene networks, and initiated the development of therapeutic approaches. The reference genome, which became available thanks to the Human Genome Project, and the development of next generation sequencing tools, considerably accelerated gene and mutation discoveries. In fact, the first clinical whole genome sequence was reported in a patient with CMT. Here we review the history of CMT gene discoveries, starting with technologies from the early days in human genetics through the high-throughput application of modern DNA analyses. We highlight the most relevant examples of CMT genes and mutation mechanisms, some of which provide promising treatment strategies. Finally, we propose future initiatives to accelerate diagnosis of CMT patients through new ways of sharing large datasets and genetic variants, and at ever diminishing costs.
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http://dx.doi.org/10.3390/genes5010013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3978509PMC
January 2014

Mutations in the ER-shaping protein reticulon 2 cause the axon-degenerative disorder hereditary spastic paraplegia type 12.

J Clin Invest 2012 Feb 9;122(2):538-44. Epub 2012 Jan 9.

Department of Human Genetics, University of Miami Miller School of Medicine, Miami, Florida, USA.

Hereditary spastic paraplegias (HSPs) are a group of genetically heterogeneous neurodegenerative conditions. They are characterized by progressive spastic paralysis of the legs as a result of selective, length-dependent degeneration of the axons of the corticospinal tract. Mutations in 3 genes encoding proteins that work together to shape the ER into sheets and tubules - receptor accessory protein 1 (REEP1), atlastin-1 (ATL1), and spastin (SPAST) - have been found to underlie many cases of HSP in Northern Europe and North America. Applying Sanger and exome sequencing, we have now identified 3 mutations in reticulon 2 (RTN2), which encodes a member of the reticulon family of prototypic ER-shaping proteins, in families with spastic paraplegia 12 (SPG12). These autosomal dominant mutations included a complete deletion of RTN2 and a frameshift mutation predicted to produce a highly truncated protein. Wild-type reticulon 2, but not the truncated protein potentially encoded by the frameshift allele, localized to the ER. RTN2 interacted with spastin, and this interaction required a hydrophobic region in spastin that is involved in ER localization and that is predicted to form a curvature-inducing/sensing hairpin loop domain. Our results directly implicate a reticulon protein in axonopathy, show that this protein participates in a network of interactions among HSP proteins involved in ER shaping, and further support the hypothesis that abnormal ER morphogenesis is a pathogenic mechanism in HSP.
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http://dx.doi.org/10.1172/JCI60560DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3266795PMC
February 2012