Inherited Peripheral Neuropathies (IPN)
Inherited peripheral neuropathies (IPN) are one of the most common hereditary disorders affecting 1 in 3000 people. There are many types of IPN and the disorder is classified based on the involvement of the motor and/or sensory nerves. The neuropathies can include hereditary sensory neuropathy (HSN), hereditary motor neuropathy (HMN) and hereditary motor and sensory neuropathy (HMSN) also known at Charcot-Marie-Tooth (CMT) neuropathy.
Charcot-Marie-Tooth (CMT) neuropathy is the most common group of the IPNs. The syndrome affects both the motor and sensory neurons. CMT is a disabling disorder that afflicts 8800 Australians for their lifetime. It, therefore, has major economic impacts in terms of productive years lost and the requirement for medical, paramedical and pension support. Motor and sensory neurons represent a unique cell type with long axons (up to 1 metre) that require continuous maintenance from the cell body to the nerve endings. The breakdown of this maintenance leads to the ‘dying back’ of nerve ends going to the extremities of the body and patients suffer gradual muscle weakness in the arms and legs as well as some loss of sensory nerve function.
Our CMT research team
A/Prof Marina Kennerson, Dr Gonzalo Perez, Obaid Albulym, Rabia Chaudhry, Clare Healy, Melina Ellis, Adrienne Grant, Aditi Kidambi, Carolyn Ly, A/Prof Stephen Reddel, Dr Alexander Drew, Prof Garth Nicholson
Identifying CMT Genes Using Family Studies
Our CMT research team at the Northcott Neuroscience Laboratory, ANZAC Research Institute has an exemplary international track record for the discovery of CMT genes. For over 20 years the laboratory has been recruiting CMT, HSN and HMN families. Through our association with the Neurogentics Clinic at Concord Hospital and being the main Australian centre for DNA testing of inherited peripheral neuropathies we have over 700 families documented in one of the largest IPN databases in the world.
Our research group has expertise in genetic linkage studies and using state of the art genome technologies for gene discovery. The overall aim of our research is to discover new genes causing CMT and to understand the underlying pathogenic biology causing the demise of the motor and sensory nerves in CMT families that do not have mutations in the known genes. By understanding the disease mechanisms this may lead to the development of treatments and therapeutic intervention for CMT. Many of our gene discoveries have been developed and implemented for diagnostic testing.
Our team is actively recruiting new families and individuals to participate in our family studies. If you or your family are interested in participating in our research, please contact Clare Healy at (02) 9767 7622 or firstname.lastname@example.org.
The following research is currently being carried out in the laboratory.
Discovering Genes for X-linked CMT (CMTX)
Approximately 15% of all CMT is inherited on the X chromosome. To date there are five known CMTX loci. The most common form CMTX1, is caused by mutations in the connexin 32 (Cx32). Our research is focused on identifying the CMTX3 gene which localises to a region on the long arm of chromosome. Through collaborations with our US colleagues, we have access to DNA samples from family that first reported the CMTX3 locus back in 1991. This resource will be extremely important for validating the CMTX3 gene mutation when it is eventually identified. The discovery of this gene will reveal mechanisms causing degeneration of long nerves. Finding new mechanisms of length dependent axonal degenerations may provide insights relevant to other neurodegenerative disorders. We have also mapped a new locus for X-linked dominant CMT in a multi-generation family. The search for the gene mutation continues with the use of exome sequencing.
Implementing New Technologies For Mutation Analysis
Mutation analysis of genes causing CMT has been expedited by the introduction of a new improved method called High Resolution Melt (HRM) analysis. The LightScanner 96 well machine from Idaho Technology USA was the first instrument to be commissioned in an Australian research institute and was the first to be purchased in the world. We have validated this technology in our laboratory and it is routinely used to identify mutations in large multi-exon genes for the most common axonal form of CMT (CMT2A; mitofusin MFN2), an intermediate form of CMT (DI-CMTB; dynamin 2 DNM2) and an X-linked form distal hereditary motor neuropathy (dHMNX; ATP7a). HRM analysis is a simple, sensitive and cost efficient method to alternative gene scanning methods and has the potential to reduce the sequencing burden of mutation discovery.
Discovering CMT Genes Using Next Generation Sequencing
Whole-exome sequencing is a new approach which utilises the power of next generation sequencing (NGS) to identify very rare variants in approximately 1% of our DNA that codes for proteins. This strategy of gene mutation identification is very useful for families with CMT as many of the mutations identified in genes causing CMT have occurred in the protein coding portion of the DNA. With this technology we have the ability to sequence over 20,000 genes in a single sequencing experiment. By sequencing key individuals in small nuclear families we can identify all the possible DNA changes in genes for these individuals and then determine which variant is the disease-causing mutation. With current NHMRC funding we have begun to use this technology in several CMT families and we have identified variants in two new genes which could potentially cause CMT. Work is currently confirming the DNA changes do in fact cause CMT disease in these families.
Copper Biology and X-linked Distal Motor Neuropathy
Our laboratory led an international collaboration in the discovery of mutations in the copper transport gene ATP7A as a cause of a distal motor neuropathy on chromosome X (Kennerson et al. 2010). The ATP7A protein is important for maintaining the balance of copper in our bodies and our discovery highlighted the importance of copper homeostasis in motor neuron function. The mutations we identified result in the ATP7A protein not trafficking (moving) correctly in the cells when exposed to high levels of copper. Our research is now involves studying neuronal cell and animal models for this motor neuropathy which may lead to the development of therapeutic strategies based on the modification of copper balance in patients with dHMNX. We have recently shown an increased interaction with the valosin-containing protein (p97VCP) which is mutated in an autosomal dominant form of motor neuron disease (Yi et al 2012).