Optimising the biocompatibility of 3D printed photopolymer constructs in vitro and in vivo.

3D printing is a rapid and accessible fabrication technology that engenders creative custom design solutions for cell scaffolds, perfusion systems and cell culture systems for tissue engineering. Critical to its success is the biocompatibility of the materials used, which should allow long-term tissue culture without affecting cell viability or inducing an inflammatory response for in vitro and in vivo applications. Polyjet 3D printers offer arguably the highest resolution with the fewest design constraints of any commercially available 3D printing systems. Although widely used for rapid-prototyping of medical devices and 3D anatomical modelling, polyjet printing has not been adopted by the tissue engineering field, largely due to the cytotoxicity of leachates from the printed parts. Biocompatibility in the context of cell culture is not commonly addressed for polyjet materials, as they tend to be optimised for their ability to fabricate complex structures. In order to study the potential issues surrounding the leaching of toxins, we prepared cell culture substrates using the commercially available MED610 photopolymer. The substrates were cleaned using either the manufacturer-specified 'biocompatible' washing procedures, or a novel protocol incorporating a sonication in isopropanol and water step. We then compared the effectiveness of these both in vitro and in vivo. Using primary mouse myoblast cultures, the manufacturer's protocol led to inconsistent and poorer cell viability when compared to the sonication protocol (p = 0.0002 at 48 h after indirect exposure). Subdermal implantation of MED610 into nude rats demonstrated a significant foreign body response with a greater number of giant cells (p = 0.0161) and foreign bodies (p = 0.0368) when compared to the sonication protocol, which was comparable to the control (sham) groups. These results present an improved, cytocompatible cleaning protocol of printable photopolymers to facilitate creative 3D-printed custom designs for cell culture systems for both in vitro and in vivo tissue engineering applications.

Conductive composite fibres from reduced graphene oxide and polypyrrole nanoparticles.

Continuous composite fibres composed of polypyrrole (PPy) nanoparticles and reduced graphene oxide (rGO) at different mass ratios were fabricated using a single step wet-spinning approach. The electrical conductivity of the composite fibres increased significantly with the addition of rGO. The mechanical properties of the composite fibres also improved by the addition of rGO sheets compared to fibres containing only PPy. The ultimate tensile strength of the fibres increased with the proportion of rGO mass present. The elongation at break was greatest for the composite fibre containing equal mass ratios of PPy nanoparticles and rGO sheets. L929 fibroblasts seeded onto fibres showed no reduction in cell viability. To further assess toxicity, cells were exposed to media that had been used to extract any aqueous-soluble leachates from developed fibre. Overall, these composite fibres show promising mechanical and electrical properties while not significantly impeding cell growth, opening up a wide range of potential applications including nerve and muscle regeneration studies.

Engineering a multimodal nerve conduit for repair of injured peripheral nerve.

Injury to nerve tissue in the peripheral nervous system (PNS) results in long-term impairment of limb function, dysaesthesia and pain, often with associated psychological effects. Whilst minor injuries can be left to regenerate without intervention and short gaps up to 2 cm can be sutured, larger or more severe injuries commonly require autogenous nerve grafts harvested from elsewhere in the body (usually sensory nerves). Functional recovery is often suboptimal and associated with loss of sensation from the tissue innervated by the harvested nerve. The challenges that persist with nerve repair have resulted in development of nerve guides or conduits from non-neural biological tissues and various polymers to improve the prognosis for the repair of damaged nerves in the PNS. This study describes the design and fabrication of a multimodal controlled pore size nerve regeneration conduit using polylactic acid (PLA) and (PLA):poly(lactic-co-glycolic) acid (PLGA) fibers within a neurotrophin-enriched alginate hydrogel. The nerve repair conduit design consists of two types of PLGA fibers selected specifically for promotion of axonal outgrowth and Schwann cell growth (75:25 for axons; 85:15 for Schwann cells). These aligned fibers are contained within the lumen of a knitted PLA sheath coated with electrospun PLA nanofibers to control pore size. The PLGA guidance fibers within the nerve repair conduit lumen are supported within an alginate hydrogel impregnated with neurotrophic factors (NT-3 or BDNF with LIF, SMDF and MGF-1) to provide neuroprotection, stimulation of axonal growth and Schwann cell migration. The conduit was used to promote repair of transected sciatic nerve in rats over a period of 4 weeks. Over this period, it was observed that over-grooming and self-mutilation (autotomy) of the limb implanted with the conduit was significantly reduced in rats implanted with the full-configuration conduit compared to rats implanted with conduits containing only an alginate hydrogel. This indicates return of some feeling to the limb via the fully-configured conduit. Immunohistochemical analysis of the implanted conduits removed from the rats after the four-week implantation period confirmed the presence of myelinated axons within the conduit and distal to the site of implantation, further supporting that the conduit promoted nerve repair over this period of time. This study describes the design considerations and fabrication of a novel multicomponent, multimodal bio-engineered synthetic conduit for peripheral nerve repair.

Inhibition of smooth muscle cell adhesion and proliferation on heparin-doped polypyrrole.

We have investigated the application of polypyrrole (pPy) as a material to influence neointimal cell behaviour. The physico-chemical properties of pPy doped with heparin (Hep), para-toluene sulfonate, poly(2-methoxyaniline-5-sulfonic acid) (pMAS) and nitrate ions were studied in addition to cell adhesion and proliferation studies of neointimal relevant cell lines cultured on the pPy substrates. Both smooth muscle (hSMC) and endothelial (hEC) cell types adhered and proliferated best on the smooth, hydrophilic pPy/pMAS material. Moreover, pPy/Hep is able to support the proliferation of hECs on the surface but inhibits hSMC proliferation after 4 days of culture. The inhibitory effect on hSMCs is most likely due to the well-known antiproliferative effect of heparin on hSMC growth. The results presented indicate that surface exposed heparin binds to the putative heparin receptor of hSMCs and is sufficient to inhibit proliferation. The application of galvanostatically synthesized pPy/Hep to stent surfaces presents a novel bioactive control mechanism to control neointimal cell growth.

Creating conductive structures for cell growth: growth and alignment of myogenic cell types on polythiophenes.

Conducting polymers provide suitable substrates for the in vitro study of excitable cells, including skeletal muscle cells, due to their inherent conductivity and electroactivity. The thiophene family of conducting polymers offers unique flexibility for tailoring of polymer properties as a result of the ease of functionalization of the parent monomer. This article describes the preparation of films and electrospun fibers from an ester-functionalized organic solvent-soluble polythiophene (poly-octanoic acid 2-thiophen-3-yl-ethyl ester) and details the changes in properties that result from post-polymerization hydrolysis of the ester linkage. The polymer films supported the proliferation and differentiation of both primary and transformed skeletal muscle myoblasts. In addition, aligned electrospun fibers formed from the polymers provided scaffolds for the guided differentiation of linearly aligned primary myotubes, suggesting their suitability as three-dimensional substrates for the in vitro engineering of skeletal muscle tissue.

Diagnostic screening of mitochondrial DNA mutations in Australian adults 1990-2001.

BACKGROUND: Many diverse pathogenic mitochondrial DNA (mtDNA) mutations have been described since 1988. The Melbourne Neuromuscular Research Institute (MNRI) has undertaken diagnostic detection of selected mtDNA mutations since 1990. MtDNA mutations screened have included point mutations associated with Leber's hereditary optic neuropathy (LHON; G3460A, G11778A and T14484C), mitochondrial encephalopathy lactic acidosis and stroke-like episodes (MELAS; A3243G), myoclonus epilepsy and ragged red fibres (MERRF; A8344G) and Leigh's syndrome/neuropathy ataxia retinitis pigmentosa (LS/NARP; T8993C/G). Samples have also been screened for deletions/ rearrangements associated with Kearns-Sayre syndrome (KSS) and chronic progressive external ophthalmoplegia (CPEO). AIMS: To present an audit of the MNRI mtDNA diagnostic service between 1990 and 2001, encompassing 1725 referred patients. METHODS: The detection techniques carried out included polymerase chain reaction amplification of mtDNA combined with restriction fragment length polymorphism analysis for mtDNA point mutation detection, supplemented with selected sequence analysis and Southern blots for the detection of deletions/ rearrangements. Tissues tested included blood, hair and skeletal muscle. RESULTS: Of the 1184 patients screened for MELAS A3243G, 6.17% were positive for the mutation, whereas for MERRF A8344G, 2.21% carried the mutation and for LS/NARP T8993C/G, 0.32% carried the mutation. The outcomes for the LHON mutations were G11778A, 6.60%, T14484C, 5.76% and G3460A, 0.29%. Of the patients referred for KSS and CPEO, 17.72% had deletions/rearrangements. CONCLUSIONS: Overall, the detection rate of mtDNA point mutations was low. The protean clinical features of mitochondrial disorders and the frequency of partial phenotypes lead to requests for tests in many patients with a relatively low likelihood of mtDNA mutations. An improved algorithm could involve mutation screening appropriate to the phenotype using sequencing of selected mtDNA regions in patients with a high likelihood of mtDNA disease. Features increasing the likelihood of mtDNA mutations include the following: (i) a typical phenotype, (ii) a maternal inheritance pattern and (iii) histochemical evidence of mitochondrial abnormality in the muscle biopsy. Efficient laboratory diagnosis of mtDNA disease involves good communication between the physician and laboratory scientists, coupled with screening of the appropriate tissue.

CD45 fraction bone marrow cells as potential delivery vehicles for genetically corrected dystrophin loci.

Targeted correction of mutations in muscle can be delivered by direct i.m. injection of corrective DNA to the dystrophic muscle or by autologous injection of cells that have been genetically corrected after isolation from the individual with the dystrophic muscle. The successful application of chimeraplasty and short fragment homologous replacement to correct the exon 23 nonsense mdx transition at the mouse dys locus has opened up the possibility that with further development, targeted gene correction may have some future application for the treatment of muscular dystrophies. In vitro, application of targeted gene correction at the mdx dys locus results in better correction efficiencies than when applied directly to dystrophic muscle. This suggests that at least for the time being, a strategy involving ex vivo correction may be advantageous over a direct approach for delivery of gene correction to dystrophic muscle. This, particularly in view of recent developments indicating that bone-marrow-derived cells are able to systemically remodel dystrophic muscle, whilst penetration of DNA introduced to muscle is limited to individually injected muscles. Application of targeted gene correction to Duchenne dystrophy needs to account for the fact that about 65% of Duchenne muscular dystrophy cases involve large frame-shift deletion of gene sequence at the dys locus. Traditionally, whilst targeted gene correction is able to restore point mutations entirely, it remains to be seen as to whether a strategy for the 'correction' of frame shift deletions may be engineered successfully. This communication discusses the possibility of applying targeted gene correction to dystrophic muscle in Duchenne dystrophy.

Targeted gene correction in the mdx mouse using short DNA fragments: towards application with bone marrow-derived cells for autologous remodeling of dystrophic muscle.

In muscle, mutant genes can be targeted and corrected directly by intramuscular (i.m.) injection of corrective DNA, or by ex vivo delivery of DNA to myogenic cells, followed by cell transplantation. Short fragment homologous replacement (SFHR) has been used to repair the exon 23 nonsense transition at the Xp21.1 dys locus in cultured cells and also, directly in tibialis anterior from male mdx mice. Whilst mdx dys locus correction can be achieved in up to 20% of cells in culture, much lower efficiency is evident by i.m. injection. The major consideration for application of targeted gene correction to muscle is delivery throughout relevant tissues. Systemically injected bone marrow (BM)-derived cells from wt C57BL/10 ScSn mice are known to remodel mdx muscle when injected into the systemic route. Provided that non muscle-derived cell types most capable of muscle remodeling activity can be more specifically identified, isolated and expanded, cell therapy seems presently the most favorable vehicle by which to deliver gene correction throughout muscle tissues. Using wt bone marrow as a model, this study investigates systemic application of bone marrow-derived cells as potential vehicles to deliver corrected (ie wt) dys locus to dystrophic muscle. Intravenous (i.v.) and intraperitoneal (i.p.) injections of wt BM were given to lethally and sub-lethally irradiated mdx mice. Despite both i.v. and surviving i.p. groups containing wt dys loci in 100% and less than 1% of peripheral blood nuclei, respectively, both groups displayed equivalent levels of wt dys transcript in muscle RNA. These results suggest that the muscle remodeling activity observed in systemically injected BM cells is not likely to be found in the hemopoietic fraction.

Presymptomatic motor neuron loss and reactive astrocytosis in the SOD1 mouse model of amyotrophic lateral sclerosis.

In familial amyotrophic lateral sclerosis (fALS), there is a need to establish more precisely the progression of the disease, particularly whether there is gradual presymptomatic neuronal loss or an abrupt loss coinciding with the symptomatic stage. To elucidate this, we investigated the progression of motor neuron loss through morphological techniques, reactive astrocytosis, and expression of ubiquitin and neurofilament proteins, by immunohistochemistry, in SOD1 G93A mice with a protracted disease course and control mice. Loss of motor neurons in SOD1 G93A mice followed a biphasic progression, with an initial loss at 126 days of age, followed by a gradual loss from onset of symptoms through to end-stage disease. Reactive astrocytosis was first observed at 70 days of age and showed a gradual increase through to end-stage disease. This suggests that there is a need for early detection of fALS cases, and potential therapeutic treatments may be more beneficial if administered at an early stage.

In vivo and in vitro correction of the mdx dystrophin gene nonsense mutation by short-fragment homologous replacement.

Targeted genetic correction of mutations in cells is a potential strategy for treating human conditions that involve nonsense, missense, and transcriptional splice junction mutations. One method of targeted gene repair, single-stranded short-fragment homologous replacement (ssSFHR), has been successful in repairing the common deltaF508 3-bp microdeletion at the cystic fibrosis transmembrane conductance regulator (CFTR) locus in 1% of airway epithelial cells in culture. This study investigates in vitro and in vivo application of a double-stranded method variant of SFHR gene repair to the mdx mouse model of Duchenne muscular dystrophy (DMD). A 603-bp wild-type PCR product was used to repair the exon 23 C-to-T mdx nonsense transition at the Xp21.1 dys locus in cultured myoblasts and in tibialis anterior (TA) from male mdx mice. Multiple transfection and variation of lipofection reagent both improved in vitro SFHR efficiency, with successful conversion of mdx to wild-type nucleotide at the dys locus achieved in 15 to 20% of cultured loci and in 0.0005 to 0.1% of TA. The genetic correction of mdx myoblasts was shown to persist for up to 28 days in culture and for at least 3 weeks in TA. While a high frequency of in vitro gene repair was observed, the lipofection used here appeared to have adverse effects on subsequent cell viability and corrected cells did not express dystrophin transcript. With further improvements to in vitro and in vivo gene repair efficiencies, SFHR may find some application in DMD and other genetic neuromuscular disorders in humans.

Myostatin, insulin-like growth factor-1, and leukemia inhibitory factor mRNAs are upregulated in chronic human disuse muscle atrophy.

Human disuse muscle atrophy frequently accompanies orthopedic injury, arthritis, or bed rest, and recovery is often incomplete despite current rehabilitation programs. We have studied the vastus lateralis muscle in 12 patients with chronic disuse atrophy associated with chronic osteoarthritis of the hip both preoperatively and after total hip arthroplasty. Semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) demonstrated an increase in the level of expression of myostatin, insulin-like growth factor-1 (IGF-1) and leukemia inhibitory factor (LIF) mRNAs compared to healthy control muscle. In all patients there was a significant correlation preoperatively between increasing myostatin mRNA expression and reduction in type 2A and 2B fiber area. In the 8 female patients there was a significant correlation between increased myostatin mRNA expression and the atrophy factor calculated for 2A and 2B fiber types preoperatively. We hypothesize that a complex interaction occurs between muscle growth regulating factors in the genesis of muscle wasting. Our results indicate that myostatin is a muscle-wasting factor contributing to type 2B and 2A atrophy. Other muscle growth factors, such as IGF-1 and LIF, may be upregulated in a counterregulatory fashion or may be involved in the fiber type switching seen in disuse muscle wasting.

A novel clinical phenotype of myopathy, sensorimotor neuropathy, infertility, and hypogonadism with multiple mitochondrial DNA deletions.

We describe a patient with myopathy, sensorimotor neuropathy, hypogonadism, and infertility with abnormal sperm mobility and morphology. Analysis of the deltoid muscle DNA revealed a G to A change at nt 1102 in the twinkle gene and multiple mitochondrial DNA deletions. Histochemistry revealed "ragged-red" fibers and many cytochrome-c oxidase negative fibers (32%) that lacked the mitochondrial encoded respiratory chain subunits I and II and the nuclear encoded subunit VIc. Respiratory chain enzyme analysis showed severe deficiency of complex I, III, and IV. This patient has no documented family history of progressive external ophthalmoplegia, which suggests either a sporadic or autosomal-recessive syndrome. This case is a novel phenotype for twinkle gene mutations and multiple mitochondrial DNA deletion syndromes, as these syndromes generally follow an autosomal-dominant inheritance pattern.

Leukemia inhibitory factor ameliorates muscle fiber degeneration in the mdx mouse.

Although the muscles of the mdx mouse lack dystrophin, the protein absent in muscles of humans affected with Duchenne muscular dystrophy (DMD), the only mdx muscle to degenerate in a manner similar to those of DMD boys is the diaphragm. We have previously shown that leukemia inhibitory factor (LIF) is a trauma factor that enhances muscle repair in vivo and, when applied exogenously, increases the fiber size of mdx skeletal muscle. Furthermore, we developed a controlled release device for LIF based on a calcium alginate rod (release rate about 0.5% per day). These rods were sutured to the abdominal surface of the hemidiaphragm of mdx mice 3 months old. At age 6 months the mice were killed and the diaphragm muscles fixed and sectioned. The sections showed obvious muscle degeneration at 3 months of age in mdx mouse diaphragms and further degeneration at 6 months in saline-perfused muscle. Hemidiaphragm muscles continuously exposed to LIF over the same period contained more normal myofibers, larger regenerated fibers, and less adipose tissue and other non-contractile tissue. Morphometric analysis of the diaphragm sections was carried out. The LIF-treated animals showed a significant increase in fiber number and size compared to saline rod controls. The amount of nonmuscle (connective tissue and adipose tissue) was significantly reduced and the maximum force-producing capacity of isolated diaphragm muscle strips was higher in LIF-treated mice. The results demonstrate that LIF treatment ameliorates the dystrophic abnormalities in mdx mouse diaphragm.

Increased levels of leukemia inhibitory factor mRNA in muscular dystrophy and human muscle trauma.

Leukemia inhibitory factor (LIF) is an important muscle trauma factor both after crush injury and in the mdx mouse dystrophy model. It is important to establish which growth factors have a role in human muscle regeneration due to potential clinical therapeutic applications. As there is limited information concerning LIF expression in human muscle, we investigated the relative levels of LIF messenger ribonucleic acid (mRNA) in human muscle injury. Semiquantitative reverse transcriptase followed by polymerase chain reaction was used to amplify LIF message. We found that although LIF mRNA is expressed in low levels in control muscle, a sevenfold increase occurred after orthopedic muscle trauma and a marked 19-fold increase in dystrophic muscle (P < 0.002). These results indicate that LIF mRNA is upregulated in surgical and especially medical muscle injury with repeated myonecrosis. Muscle growth factors such as LIF may assist in future muscle rehabilitation after injury.

Mitochondrial respiratory chain activity in idiopathic dilated cardiomyopathy.

BACKGROUND: Cardiomyopathy is well recognized in mitochondrial diseases in which it has been associated with defects of mitochondrial function, including cytochrome-c oxidase (COX) deficiencies. This study explores the respiratory chain activity, particularly of COX, in patients with cardiomyopathy to determine whether a relationship exists between respiratory enzyme activity and cardiac function. METHODS AND RESULTS: Myocardial specimens from the left ventricular wall of explanted hearts were obtained from subjects with ischemic (n = 6) or nonischemic dilated (n = 8) cardiomyopathy. Assays for citrate synthase (CS) and complexes II/III and IV activity were performed on cardiac mitochondria and homogenate. Enzyme activities were normalized to CS activity and compared with control activities (n = 10). A significant reduction in COX and/or CS activity was identified in mitochondrial preparations from the transplant group and correlated significantly with ejection fraction (P < .05), although this does not prove a causal relationship. Significantly reduced CS activity in homogenate was identified, suggesting decreased mitochondrial volume in addition to decreased COX activity. Measurements in cardiac homogenates failed to show a significant reduction in COX activity (P > .05) in the transplant group, suggesting that the use of prefrozen tissue homogenates may underestimate existing mitochondrial respiratory defects in cardiac tissue. CONCLUSIONS: Mitochondrial function is altered at a number of levels in end-stage cardiomyopathy. Defective COX activity resulting in deficient adenosine triphosphate generation may contribute to impaired ventricular function in heart failure. Agents capable of improving mitochondrial function may find an adjuvant role in the treatment of cardiac failure.

mtDNA replicative potential remains constant during ageing: polymerase gamma activity does not correlate with age related cytochrome oxidase activity decline in platelets.

Progressive age-related oxidative phosphorylation (OxPhos) decline is well known in human tissues. Depletion of mitochondrial DNA (mtDNA) causes OxPhos defects in patients with myopathic syndromes and deficient mtDNA replication has been observed in cells cultured from patients with mitochondrial disease. Patients undergoing treatment for AIDS develop OxPhos defects via mtDNA depletion resulting from inhibition of mtDNA polymerase gamma (Polgamma) by 2'-deoxy 3'-azido thymidine. These findings by others give rise to a possible link between mtDNA replication and bioenergetic decline in disease and during ageing. We have designed an in vitro assay for Polgamma function in small tissue samples to explore this possible link. Platelet homogenate Polgamma showed an activity with a K m of 150 microM (dTTP), a V max of 11.8 pmol/min/mg, inhibited (41% inhibition; 50 microM) by ethidium bromide. Determination of several storage characteristics showed that platelets were a convenient source of Polgamma for assay. Polgamma activity in 45 subjects did not coincide with significant age-related decline (P<0.002; P) observed in cytochrome oxidase (CytOx) activity or with citrate synthase activity. Of the activities studied, the only significant age-wise variation was a 24% CytOx deficiency in elderly (>50; n = 19) compared to young (<51; n = 24) individuals (P<0.01; t). These results suggest a maintenance of total cellular mtDNA Polgamma processive levels during ageing, largely independent of total cellular bioenergetic status or mitochondrial number/density. The processive component of Polgamma is therefore unlikely to make a major contribution to age-related bioenergetic activity decline. This does not, however, preclude the possibility that transient periods of inhibition at crucial points of the cell cycle or development may augment existing intracellular deficiencies. The assay described here greatly facilitates study of Polgamma activity in patients with conditions involving mtDNA depletion or rearrangement.

Detection of MELAS A3243G point mutation in muscle, blood and hair follicles.

Polymerase chain reaction (PCR) based methods for the diagnosis and screening of the mitochondrial disorders have been well established. A number of tissues are routinely used. In this study, we compared the detection rate for MELAS A3243G point mutation in muscle, blood and hair follicles. Ten subjects were studied; mean age was 47 years, (SD 16, range 23-73). All ten subjects had the MELAS A3243G point mutation detected in muscle and hair follicles, but only five had the abnormality in blood samples. The rate of detection of the point mutation in blood samples was age dependent. MtDNA analysis on hair follicles is as sensitive as muscle in detecting this mutation. Analysis using blood samples is not as sensitive, particularly in older subjects. The absence of the mutation in blood samples suggests that there is a preferential selection process for normal (wild type) mtDNA over time. This may be related to the rate of cell division and energy requirements of each tissue.

Developmental genetics of deleted mtDNA in mitochondrial oculomyopathy.

Heteroplasmic populations of mtDNA, consisting of normal mtDNA and mtDNA with large deletions, are found in the skeletal muscle and other tissues of certain patients with mitochondrial respiratory chain deficiencies, particularly in those with the CPEO (chronic progressive external ophthalmoplegia) phenotype. To study the developmental genetics of this mitochondrial disorder, the distribution of the deleted mtDNA in a wide range of tissues of different embryonic origins (total 34 samples from 27 tissues obtained at autopsy) was investigated in a patient with the CPEO syndrome. Three species of partially deleted mtDNA were observed, with deletions of 2.3 kb, 5.0 kb and 6.4 kb. Their tissue distribution suggests that the mtDNA deletions have occurred very early during embryonic development, prior to the differentiation events that lead to the formation of the three primary embryonic germ layers, and that the partially deleted mtDNA species were segregated during development mainly to the skeletal muscle and to tissues of the central nervous system.

The polymerase chain reaction in the study of mitochondrial genetics.

Since its development in the late 1980's, the polymerase chain reaction (PCR) has revolutionised molecular genetic studies. It has provided direct access to genetic material in quantities sufficient for meaningful analyses to be performed. Adaptations to the basic technique have resulted in a wide range of applications from basic gene amplification to the estimation of DNA species quantities within cells. The study of human mitochondrial genetics is but one of the many disciplines to benefit from the rapid ascension of PCR based technology. In this communication we outline several uses of the PCR technique in the detection, quantification and characterisation of human mitochondrial genetic defects. The data presented in this communication highlight the versatility and applicability of PCR not only to mitochondrial research but to other disciplines of medical research.