Ischemia-reperfusion injury and pregnancy initiate time-dependent and robust signs of up-regulation of cardiac progenitor cells

To explore how cardiac regeneration and cell turnover adapts to disease, different forms of stress were studied for their effects on the cardiac progenitor cell markers c-Kit and Isl1, the early cardiomyocyte marker Nkx2.5, and mast cells. Adult female rats were examined during pregnancy, after myocardial infarction and ischemia-reperfusion injury with/out insulin like growth factor-1(IGF-1) and hepatocyte growth factor (HGF). Different cardiac sub-domains were analyzed at one and two weeks post-intervention, both at the mRNA and protein levels. While pregnancy and myocardial infarction up-regulated Nkx2.5 and c-Kit (adjusted for mast cell activation), ischemia-reperfusion injury induced the strongest up-regulation which occurred globally throughout the entire heart and not just around the site of injury. This response seems to be partly mediated by increased endogenous production of IGF-1 and HGF. Contrary to c-Kit, Isl1 was not up-regulated by pregnancy or myocardial infarction while ischemia-reperfusion injury induced not a global but a focal up-regulation in the outflow tract and also in the peri-ischemic region, correlating with the up-regulation of endogenous IGF-1. The addition of IGF-1 and HGF did boost the endogenous expression of IGF and HGF correlating to focal up-regulation of Isl1. c-Kit expression was not further influenced by the exogenous growth factors. This indicates that there is a spatial mismatch between on one hand c-Kit and Nkx2.5 expression and on the other hand Isl1 expression. In conclusion, ischemia-reperfusion injury was the strongest stimulus with both global and focal cardiomyocyte progenitor cell marker up-regulations, correlating to the endogenous up-regulation of the growth factors IGF-1 and HGF. Also pregnancy induced a general up-regulation of c-Kit and early Nkx2.5+ cardiomyocytes throughout the heart. Utilization of these pathways could provide new strategies for the treatment of cardiac disease.

Generation of Hepatocyte-Like Cells from in Vitro Transdifferentiated Human Fetal Pancreas

Although the appearance of hepatic foci in the pancreas has been described in animal experiments and in human pathology, evidence for the conversion of human pancreatic cells to liver cells is still lacking. We therefore investigated the developmental plasticity between human embryonic pancreatic cells and liver cells. Cells were isolated and expanded from 7–8-week-old human fetal pancreata (HFP) and were characterized for the absence and presence of pancreatic and hepatic markers. In vitro expanded HFP were treated with fibroblast growth factor 2 (FGF2) and dexamethasone (DX) to induce a liver phenotye in the cells. These treated cells in various passages were further studied for their capacity to be functional in hepatic parenchyma following retrorsine-induced injury in nude C57 black mice. Amylase- and EPCAM-positive-enriched cells isolated from HFP and treated with FGF2 and DX lost expression of pancreatic markers and gained a liver phenotype. Hepatic differentiation was based on the expression (both at the mRNA and protein level) of liver markers albumin and cytokeratin 19. When transplanted in vivo into nude mice treated with retrorsine, both cell types successfully engrafted and functionally differentiated into hepatic cells expressing human albumin, glycogen, dipeptidyl peptidase, and γ-glutamyltranspeptidase. These data indicate that human fetal pancreatic cells have a capacity to alter their gene expression profile in response to exogenous treatment with FGF2 and DX. It may be possible to generate an unlimited supply of hepatocytes in vitro for cell therapy.

Evidence for no relevance of anti-major histocompatibility complex class I-related chain a antibodies in liver transplantation

The polymorphic major histocompatibility complex class I-related chain A (MICA) antigen is being increasingly recognized as a potential target molecule for immune cells during allograft rejection. Here we studied whether MICA is a target antigen for antibodies in liver transplant patients. Eighty-four patients were investigated for the presence of MICA antibodies before and after liver transplantation with MICA-transfected cells and flow cytometry. MICA typing was performed by polymerase chain reaction. Expression of MICA in liver cells was determined by reverse-transcription polymerase chain reaction, Western blotting, and flow cytometry. Liver biopsy specimens from liver transplant patients were examined for MICA expression. A total of 22 of 84 (26%) patients had MICA antibodies either pre-transplant (8/84, 9.5%) or post-transplant (14/84, 17%). No correlation between rejection frequencies (14/22, 63%) or other clinical parameters was observed in patients with MICA antibody versus those without MICA antibody (29/62, 47% P = not significant). We found weak messenger RNA expression for MICA in liver cells but no protein or cell surface expression. In addition, no MICA expression in liver biopsy sections from liver transplant patients was observed at any time point, including rejections. Thus, our preliminary results demonstrate no causal relationship between the presence of MICA antibodies and liver allograft rejections. Therefore, it is likely that MICA may not be an important target antigen during liver allograft rejections.

Cell cycle-dependent variation of a CD133 epitope in human embryonic stem cell, colon cancer, and melanoma cell lines

CD133 (Prominin1) is a pentaspan transmembrane glycoprotein expressed in several stem cell populations and cancers. Reactivity with an antibody (AC133) to a glycoslyated form of CD133 has been widely used for the enrichment of cells with tumor-initiating activity in xenograph transplantation assays. We have found by fluorescence-activated cell sorting that increased AC133 reactivity in human embryonic stem cells, colon cancer, and melanoma cells is correlated with increased DNA content and, reciprocally, that the least reactive cells are in the G(1)-G(0) portion of the cell cycle. Continued cultivation of cells sorted on the basis of high and low AC133 reactivity results in a normalization of the cell reactivity profiles, indicating that cells with low AC133 reactivity can generate highly reactive cells as they resume proliferation. The association of AC133 with actively cycling cells may contribute to the basis for enrichment for tumor-initiating activity.

Biliary epithelial cell antibodies link adaptive and innate immune responses in primary sclerosing cholangitis

BACKGROUND & AIMS

Primary sclerosing cholangitis (PSC) is an autoimmune liver disease with destruction of hepatic bile ducts. A high frequency of biliary epithelial cell antibodies (BEC-Ab) is present in PSC. Here, we studied the mechanisms and signaling pathways used by these Ab in causing BEC dysfunction.

METHODS

Immunoassays were performed using freshly isolated BECs to study the signaling capacity of purified immunoglobulin (Ig) G and F(ab)'(2) fractions from 33 patients with PSC with anti-BEC-Ab.

RESULTS

We provide evidence that stimulation of BECs with PSC IgG, but not control IgG, induced expression of Toll-like receptor (TLR) 4 and TLR9 and specific phosphorylation of extracellular signal-regulated kinase (ERK) 1/2 as well as the transcription factors ELK-1 and nuclear factor kappaB. A specific inhibitor of ERK1/2 abrogated phosphorylation of ELK-1 and protein expression of TLR4 but not TLR9 on BECs. TLR-expressing BECs, when further stimulated with lipopolysaccharide and CpG DNA, produced high levels of interleukin-1beta, interleukin-8, interferon gamma, tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor, and transforming growth factor beta. Bile ducts stained positively for TLR4 and TLR9 in 58% of liver specimens taken from patients with PSC with BEC-Ab, as compared with 14% in those without BEC-Ab and also less frequently in diseased control livers.

CONCLUSIONS

Our data show that binding of PSC BEC-Ab initiates ERK1/2 signaling and up-regulation of TLR, which upon ligation induces BECs to produce cytokines/chemokines, leading to the possible recruitment of inflammatory cells. Thus, in PSC, BECs are not only targets of the immune attack but may also be active participants and mediators of their own destruction. BEC-Ab may be critical regulators of cholangitis in PSC.

Leigh syndrome caused by mutations in the flavoprotein (Fp) subunit of succinate dehydrogenase (SDHA)

Detailed clinical, neuroradiological, histological, biochemical, and genetic investigations were undertaken in a child suffering from Leigh syndrome. The clinical symptoms started at age five months and led to a severe progressive neurodegenerative disorder causing epilepsy, psychomotor retardation, and tetraspasticity. Biochemical measurement of skeletal muscle showed a severe decrease in mitochondrial complex II. Sequencing of SDHA revealed compound heterozygosity for a nonsense mutation in exon 4 (W119X) and a missense mutation in exon 3 (A83V), both absent in normal controls. In six additional patients--five with Leigh or Leigh-like syndrome and one with neuropathy and ataxia associated with isolated deficiency of complex II--mutations in SDHA were not detected, indicating genetic heterogeneity.

Mutations in mtDNA-encoded cytochrome c oxidase subunit genes causing isolated myopathy or severe encephalomyopathy

We report on clinical, histological and genetic findings in two patients carrying novel heteroplasmic mutations in the mitochondrial cytochrome c oxidase subunit genes COII and COIII. The first patient, a 35 year-old man had a multisystemic disease, with clinical symptoms of bilateral cataract, sensori-neural hearing loss, myopathy, ataxia, cardiac arrhythmia, depression and short stature and carried a 7970 G>T (E129X) nonsense mutation in COII. A sudden episode of metabolic encephalopathy caused by extremely high blood lactate lead to coma. The second patient developed exercise intolerance and rhabdomyolysis at age 22 years. A heteroplasmic missense mutation 9789 T>C (S195P) was found in skeletal muscle, but not in blood and myoblasts pointing to a sporadic mutation. Our report of two patients with isolated COX deficiency and new mutations in COX subunit genes may help to draw more attention to this type of mtDNA defects and provide new aspects for counselling affected families.

Characterization of cells in the developing human liver

Human hepatic progenitor cells (HPCs) have been shown to co-express the hematopoietic stem cell (HSC) markers, CD117 and CD34. These cells differentiate not only into hepatocytes and cholangiocytes but also into pancreatic ductal and acinar cells under certain conditions. The fetal liver (FL) is rich in precursor/stem cells; however, little is known about (i) the markers expressed by liver cells during fetal development and (ii) whether an equivalent to the adult liver stem-like progenitors exists in the FL. Here, (i) FL tissue obtained from human 5-18-week-old fetuses were evaluated by means of flow cytometry, immunocyto-, and histochemistry for the emergence of cells expressing and co-expressing known hematopoietic, hepatic, and pancreatic cell markers, and (ii) isolated putative HPCs were phenotypically and molecularly characterized. We report that (i) red blood and endothelial cell precursors were most abundant in early gestation. Cells expressing HSC and pancreatic markers were found in the first trimester, while cells expressing hepatic markers appeared in the second trimester. Very few committed cells were present in FLs obtained early in the first trimester. In addition, cells expressing pancreatic markers co-expressed the HSC marker CD117. (ii) Isolated CD117+/CD34+/CD90- cells in vitro expressed both the genes and proteins for the hepatic markers such as albumin, alpha feto protein (AFP), alpha1-antitrypsin, and cytokeratin 19 (CK19). Our study suggests that hepatoblast and ductal plate/bile duct development mainly occurs during the second trimester. FLs in gestation weeks 5-9 had the highest numbers of precursor cells and the least committed cells. Cells that differentiate into Alb+ or CK19+ can be isolated from early FLs and may be appropriate progenitors for establishing novel systems to investigate basic mechanisms for cell therapy.

Molecular monitoring of T-cell chimerism early after allogeneic stem cell transplantation may predict the occurrence of acute GVHD grades II-IV

Mixed chimerism (MC) within CD4+ and CD8+ T cell days 7 and 10 after allogeneic stem cell transplantation (SCT) was compared with the occurrence of acute graft-vs.-host disease (GVHD) in 34 patients after SCT. Acute GVHD was diagnosed in 22 patients within the first 3 months after SCT, 15 of these developed acute GVHD grades II-IV. The difference in the clearance rate of host T cell between the two days were compared. We found a significantly higher risk (p = 0.005) for developing acute GVHD grades II-IV in patients with complete donor CD4+ T-cell chimerism day 7 after SCT together with patients who increased 50% or more in donor CD4+ T cells between days 7 and 10 after SCT. Our data suggest that molecular monitoring of MC early after transplantation may be useful as a diagnostic tool in predicting the occurrence of moderate to severe acute GVHD after SCT.

Identification of expandable human hepatic progenitors which differentiate into mature hepatic cells in vivo

BACKGROUND

Liver diseases include a wide spectrum of both acute and chronic conditions which are associated with significant morbidity and mortality worldwide. Hepatocyte transplantation has therapeutic potential in the treatment of liver diseases, but its clinical use is hampered by the lack of donor tissue. Generation of hepatocytes in vitro from adult or fetal liver cell progenitors or, alternatively, identification of a progenitor population which in vivo can generate mature liver cells could solve this problem.

METHODS

CD117+/CD34+/Lin- human fetal liver cells were isolated by magnetic cell sorting and expanded in culture. Both freshly isolated and in vitro expanded cells in various passages were studied for their ability to be functional in hepatic parenchyma following d-galactosamine (GalN) induced injury in nude C57 black mice.

RESULTS

Freshly isolated and in vitro expanded CD117+/CD34+/Lin- cells, when transplanted intrasplenically into GalN treated mice, morphologically and functionally differentiated into hepatocytes and cholangiocytes. Human specific albumin, alpha fetoprotein, cytokeratin 19, and antitrypsin mRNA were expressed in mouse liver. In addition, the human progenitor cells expressed glucose-6-phosphatase, glycogen, albumin, gamma glutamyl transpeptidase, and dipeptidyl peptidase IV after transplantation. Expanded cells in various passages maintained their capacity to differentiate into functional liver cells.

CONCLUSIONS

Fetal liver CD117+/CD34+/Lin- progenitors and their progeny proliferated in vitro and also functionally differentiated into mature hepatic cells in an acute liver injury model. Successful in vitro expansion of liver progenitor cells provides a basis for developing cell therapy strategies, metabolic and toxicity testing systems, and may serve as a vehicle for gene therapy.

The Pathophysiology of Acute Graft-Versus-Host Disease

Despite improvements in allogeneic stem cell transplantation, acute graft-versus-host disease (GVHD) remains a significant problem after transplantation, and it is still a major cause of post-transplant mortality. Disease progression is characterized by the differentiation of alloreactive T cells to effector cells leading to tissue damage, recruitment of additional inflammatory cell populations and further cytokine dysregulation. To make the complex process of acute GVHD more explicit, the pathophysiology of acute GVHD is often divided into three different phases. This review summarizes the mechanisms involved in the three phases of acute GVHD.

Increased gene expression of chemokine receptors is correlated with acute graft-versus-host disease after allogeneic stem cell transplantation

Acute graft-versus-host disease (GVHD) is still a major complication after allogeneic stem cell transplantation. It is initiated by infiltrating donor T cells specific against the host antigens. Because T-cell migration is largely controlled by the expression of chemokines and chemokine receptors, we investigated the relation of acute GVHD and chemokine receptor expression in peripheral blood in 50 patients after allogeneic stem cell transplantation. The gene expression of the chemokine receptors CCR1, CCR2, CCR5, and CXCR3 was monitored by using quantitative real-time polymerase chain reaction. Among the 36 patients diagnosed with acute GVHD, 10 developed a second episode of acute GVHD. Therefore, gene-expression levels could be analyzed in 46 occasions of acute GVHD. When all 4 markers were evaluated at the same time, increased gene-expression levels of at least 1 of the 4 markers were seen in 44 of 46 episodes of acute GVHD. The median increase of the 4 markers ranged from 3x to 12x in connection with acute GVHD. It is interesting to note that we saw increasing gene-expression levels a few days before acute GVHD was diagnosed clinically at 17, 15, 22, and 19 occasions for CCR5, CXCR3, CCR1, and CCR2, respectively. The median number of days before diagnosis ranged from 3 to 5. Although they are not specific for acute GVHD, quantitative monitoring of the gene expression of chemokine receptors may be a valuable molecular method to monitor and diagnose acute GVHD.

Congenital cataract, muscular hypotonia, developmental delay and sensorineural hearing loss associated with a defect in copper metabolism

Deficiencies of different proteins involved in copper metabolism have been reported to cause human diseases. Well-known syndromes, for example, are Menkes and Wilson diseases. Here we report a patient presenting with congenital cataract, severe muscular hypotonia, developmental delay, sensorineural hearing loss and cytochrome-c oxidase deficiency with repeatedly low copper and ceruloplasmin levels. These findings were suggestive of a copper metabolism disorder. In support of this, the patient's fibroblasts showed an increased copper uptake with normal retention. Detailed follow-up examinations were performed. Immunoblotting for several proteins including ATP7A (MNK or Menkes protein), ATP7B (Wilson protein) and SOD1 showed normal results, implying a copper metabolism defect other than Wilson or Menkes disease. Sequence analysis of ATOX1 and genes coding for proteins that are known to play a role in the mitochondrial copper metabolism (COI-III, SCO1, SCO2, COX11, COX17, COX19) revealed no mutations. Additional disease genes that have been associated with cytochrome-c oxidase deficiency were negative for mutations as well. As beneficial effects of copper histidinate supplementation have been reported in selected disorders of copper metabolism presenting with low serum copper and ceruloplasmin levels, we initiated a copper histidinate supplementation. Remarkable improvement of clinical symptoms was observed, with complete restoration of cytochrome-c oxidase activity in skeletal muscle.

Two families with autosomal dominant progressive external ophthalmoplegia

OBJECTIVES

We report here the clinical and genetic features of two new families with autosomal dominant progressive external ophthalmoplegia (adPEO).

PATIENTS AND METHODS

The examination of index patients included a detailed clinical characterisation, histological analysis of muscle biopsy specimens, and genetic testing of mitochondrial and nuclear DNA extracted from muscle and leucocytes.

RESULTS

Index patients in both families presented with PEO and developed other clinical disease manifestations, such as myopathy and cardiomyopathy (patient 1) and axonal neuropathy, diabetes mellitus, hearing loss, and myopathy (patient 2), later in the course of illness. Both patients had ragged red fibres on muscle histology. Southern blot of mtDNA from muscle of patient 2 showed multiple deletions. In this case, a novel heterozygous missense mutation F485L was identified in the nuclear encoded putative mitochondrial helicase Twinkle. The mutation co-segregated with the clinical phenotype in the family and was not detected in 150 control chromosomes. In the other index patient, sequencing of ANT1, C10orf2 (encoding for Twinkle), and POLG1 did not reveal pathogenic mutations.

CONCLUSIONS

Our cases illustrate the clinical variability of adPEO, add a novel pathogenic mutation in Twinkle (F485L) to the growing list of genetic abnormalities in adPEO, and reinforce the relevance of other yet unidentified genes in mtDNA maintenance and pathogenesis of adPEO.

Increased immune transcript levels are correlated with acute graft-versus-host disease and cytomegalovirus response after allogeneic stem cell transplantation

BACKGROUND

Donor T cells are primarily responsible for graft-versus-host disease (GVHD). Three effector pathways have been described for T-cell cytotoxicity: granzyme B/perforin, Fas/Fas ligand (FasL), and secreted molecules such as tumor necrosis factor (TNF)-alpha. Therefore, this study evaluates the gene expression pattern in the peripheral blood of patients after allogeneic stem cell transplantation and correlates the results to acute GVHD.

METHODS

Real-time quantitative reverse transcriptase-polymerase chain reaction was used to quantify the gene expression of granzyme B, perforin, FasL, and TNF-alpha in peripheral blood from 53 patients.

RESULTS

Samples were available from 27 of the 38 patients with acute GVHD diagnoses. Increased gene expression (>50%) during acute GVHD was detected in 23 of 27, 26 of 27, and 24 of 27 patients for granzyme B, perforin, and FasL, respectively. TNF-alpha showed a diffuse correlation. The median increases were as follows: granzyme B, 7.2x (1.6-183.2); perforin, 5.8x (1.6-254.9); and FasL, 8.5x (1.5-895.6). We also showed that all of the 10 patients with increasing levels of granzyme B, perforin, and FasL during steroid treatment demonstrated persistent or deteriorating GVHD. Patients with increasing transcription levels during cytomegalovirus (CMV) reactivation responded significantly better to therapy than those with declining levels. A total of 13 of 17 patients with increasing levels versus 0 of 11 patients with decreasing levels responded well to CMV treatment (P<0.01).

CONCLUSION

Although not specific for acute GVHD, quantitative assessment of immune transcripts may be of value in diagnosing and monitoring acute GVHD. It may also serve as a guide for the clinician in detecting patients who respond poorly to CMV therapy.

Reversion of hypertrophic cardiomyopathy in a patient with deficiency of the mitochondrial copper binding protein Sco2: is there a potential effect of copper?

Mutations in Sco2, a protein involved in copper trafficking to the terminal enzyme of the respiratory chain, cytochrome c oxidase, results in infantile hypertrophic cardioencephalomyopathy. We have recently shown that copper-histidine (Cu-his) supplementation of Sco2-deficient myoblasts rescues COX activity in vitro. Here, we report a patient with SCO 2 mutations and with resolution of severe hypertrophic cardiomyopathy. Weighing up the evidence, the most likely explanation for the improved cardiac function in this patient was the subcutaneous application of Cu-his.

Minimal residual disease detection after allogeneic stem cell transplantation is correlated to relapse in patients with acute lymphoblastic leukaemia

Minimal residual disease (MRD) assessments were performed retrospectively after allogeneic stem cell transplantation (SCT) in 32 patients (23 children and nine adults) with acute lymphoblastic leukaemia (ALL). Using immunoglobulin and T-cell receptor rearrangements as clonal markers, MRD was detected after SCT in nine patients, eight of whom have relapsed. The median time between first MRD detection and relapse was 5.5 (range 0.5-30) months. In 23 patients without MRD, six have relapsed to date: lower sensitivity, central nervous system relapse and clonal exchange of the leukaemic clone were factors that may explain the failure to detect MRD before relapse in these patients. In univariate analysis, factors associated with decreased risk of relapse were transplantation in first remission (P=0.02), the combination of acute and chronic graft-versus-host disease (P=0.03) and absence of MRD after SCT (P=0.005). In multivariate analysis, only MRD detection after SCT was significantly associated with increased risk of relapse (P=0.05). In conclusion, MRD detection after SCT is correlated with relapse and provides the opportunity for initiating immunotherapeutic intervention at an early stage when the tumour cell burden is still low.

Serum levels of cytokines correlate to donor chimerism and acute graft-vs.-host disease after haematopoietic stem cell transplantation

BACKGROUND

Some patients become full donor chimeras (DC) early after stem-cell transplantation (SCT), while others remain mixed chimeras for a longer time. Little is known about the mechanism behind these phenomena.

METHODS

Serum cytokine levels during conditioning and during the first month after SCT were analysed in 30 patients. Of the 21 patients who became full T-cell DC from the first analysed sample, 12 developed grade II-IV acute graft-vs.-host disease (GVHD) and the other nine, mild or no acute GVHD. Another nine patients were T-cell mixed chimeras (MC). All MC patients had no or mild acute GVHD.

RESULTS

During the pretransplant conditioning, DC patients had higher levels of tumour necrosis factor (TNF)-alpha and lower levels of transforming growth factor (TGF)-beta and interleukin (IL)-10, compared with MC patients. During the first week after SCT, lower levels of TGF-beta and IL-10 and higher levels of soluble Fas (sFas) were found in DC patients compared with MC patients. During the second and third weeks after SCT, increased levels of TNF-alpha, interferon (IFN)-gamma and sFas were found among DC patients compared with MC patients. Patients who developed moderate-to-severe acute GVHD had higher levels of TNF-alpha, IFN-gamma, IL-10 and sFas at 2 weeks post-SCT than in those with less GVHD. Patients homozygous for the TNFd microsatellite alleles 3 or 4 had significantly higher TNF-alpha levels during conditioning and more often developed acute GVHD grades II-IV.

CONCLUSION

These results indicate that an imbalance between pro-inflammatory and immune- modulating cytokines are involved in the development of chimerism and acute GVHD after allo-SCT. The Fas/FasL pathway is probably involved in the elimination of recipient cells leading to full donor chimerism.

Increased levels of immune transcript in patients with acute GVHD after allogeneic stem cell transplantation

After allogeneic stem cell transplantation (SCT), donor T-cells are primarily responsible for the antihost activity, resulting in graft-versus-host disease (GVHD). Three effector pathways have been described for T-cell cytotoxicity: perforin/granzyme B; Fas/Fas ligand (FasL) and secreted molecules such as TNF-alpha. The goal of this pilot study was to utilize competitive reverse transcription (RT)-PCR to evaluate the pattern of granzyme B, perforin, FasL and TNF-alpha gene expression in peripheral blood in patients after SCT. Protein levels of granzyme B, soluble FasL (sFasL) and TNF-alpha in plasma were also analyzed. Eight patients who underwent allogeneic SCT were included; five were diagnosed with acute GVHD. In the patients diagnosed with acute GVHD, we found increased levels of granzyme B, perforin and FasL mRNA, although this did not correlate with the clinical severity. However, patients with increasing levels of gene expression during acute GVHD treatment may have an increased risk of developing severe acute GVHD, as two out of three patients with increasing immune transcript levels during GVHD therapy developed life-threatening acute GVHD. In conclusion, the quantitative RT-PCR of granzyme B, perforin and FasL may serve as a guide to the clinician in diagnosing acute GVHD and monitoring treatment.

Myofibrillar (desmin-related) myopathy: clinico-pathological spectrum in 3 cases and review of the literature

Myofibrillar or desmin-related myopathies encompass neuromuscular disorders with abnormal deposits of desmin and myofibrillar alterations. We report 3 unrelated patients presenting with proximal and distal myopathy, and, as a unique congenital syndrome, diffusely distributed myopathy, osteoporosis and myopia. Muscle biopsies shared cytoplasmic inclusions, rimmed vacuoles, and ragged-red-like fibers. Sarcoplasmic inclusions, either plaque-like or amorphous, strongly immunoreacted on dystrophin and variably for desmin, alphaB crystallin and ubiquitin. Cyclin-dependent kinases CDK1, CDK2 and CDK5 were overexpressed in affected fibers. Ultrastructurally, focal myofibrillar disruption was accompanied by tubulo-filamentous inclusions in one case and abundant glycogen and enlarged mitochondria displaying respiratory chain dysfunction at biochemistry in another case. Molecular analysis of the alphaB crystallin gene coding sequence and exons 4, 5 and 6 of the desmin gene did not reveal any mutation. The morphologic denominator of hyaline structures and areas of myofibrillar destruction occurs in heterogeneous conditions and may overlap with features of inclusion body myopathy and mitochondrial myopathy.

Nail-patella syndrome associated with respiratory chain disorder

Nail-patella syndrome (NPS) has not been described to be associated with a respiratory chain disorder (RCD) before. In a 42-year-old man with the typical phenotype of an NPS, weakness and wasting of the shoulder girdle muscles, muscle cramps, fatigability, hyperhidrosis, chest pain and creatine kinase elevation were observed. Echocardiography revealed left ventricular hypertrabeculation. Needle electromyography was myopathic, lactate stress testing was abnormal, muscle biopsy showed typical features of an RCD and mtDNA analysis revealed the A3243G MELAS mutation. In conclusion, this case demonstrates that NPS may be randomly associated with RCD. NPS patients should undergo detailed cardiological and neurological investigations, in order not to overlook a double trouble partially mimicking NPS.

Cytochrome c oxidase deficiency due to mutations in SCO2, encoding a mitochondrial copper-binding protein, is rescued by copper in human myoblasts

Mutations in SCO2, a cytochrome c oxidase (COX) assembly gene, have been reported in nine infants with early onset fatal cardioencephalomyopathy and a severe COX deficiency in striated muscle. Studies on a yeast homolog have suggested that human Sco2 acts as a copper chaperone, transporting copper to the Cu(A) site on the Cox II subunit, but the mechanism of action remains unclear. To investigate the molecular basis of pathogenesis of Sco2 defects in humans we performed genetic and biochemical studies on tissues, myoblasts and fibroblasts from affected patients, as well as on a recombinant human C-terminal Sco2 segment (22 kDa), bearing the putative CxxxC metal-binding motif. Recombinant Sco2 was shown to bind copper with a 1:1 stoichiometry and to form homomeric complexes in vitro, independent of the metal-binding motif. Immunohistochemistry using antibodies directed against different COX subunits showed a marked tissue-specific decrease in the Cox II/III subunits that form part of the catalytic core, consistent with the differential tissue involvement, but a more uniform distribution of Cox Vab, a nuclear-encoded subunit. Sco2 was severely reduced in patient fibroblasts and myoblasts by immunoblot analysis. Patient fibroblasts showed increased (64)Cu uptake but normal retention values and, consistent with this, the copper concentration was four times higher in Sco2-deficient myoblasts than in controls. COX activity in patient myoblasts was completely rescued by transduction with a retroviral vector expressing the human SCO2 coding sequence, and more interestingly by addition of copper-histidine (300 microM) to the culture medium. Whether the latter is accomplished by the very low residual levels of Sco2 in the patient cells, direct addition of copper to the Cu(A) site, or by another copper-binding protein remains unknown. Whatever the mechanism, this result suggests a possible therapy for the early treatment of this fatal infantile disease.

Valproic acid triggers acute rhabdomyolysis in a patient with carnitine palmitoyltransferase type II deficiency

A 47-year-old man suffering from a bipolar disorder and intermittent myoglobinuria presented with acute rhabdomyolysis with renal failure after starting therapy with valproic acid. On morphological examination, skeletal muscle revealed increased lipid storage. Biochemically, decreased enzyme activity of carnitine palmitoyltransferase (CPT) type II with carnitine levels in the lower limit was found. Genetic analysis detected the common Ser113Leu substitution on one allele of the CPT2 gene. We conclude that valproic acid should be avoided in patients with CPT type II deficiency.

Homozygosity (E140K) in SCO2 causes delayed infantile onset of cardiomyopathy and neuropathy

OBJECTIVE

To report three unrelated infants with a distinctive phenotype of Leigh-like syndrome, neurogenic muscular atrophy, and hypertrophic obstructive cardiomyopathy. The patients all had a homozygous missense mutation in SCO2.

BACKGROUND

SCO2 encodes a mitochondrial inner membrane protein, thought to function as a copper transporter to cytochrome c oxidase (COX), the terminal enzyme of the respiratory chain. Mutations in SCO2 have been described in patients with severe COX deficiency and early onset fatal infantile hypertrophic cardioencephalomyopathy. All patients so far reported are compound heterozygotes for a missense mutation (E140K) near the predicted CxxxC metal binding motif; however, recent functional studies of the homologous mutation in yeast failed to demonstrate an effect on respiration.

METHODS

Here we present clinical, biochemical, morphologic, functional, MRI, and MRS data in two infants, and a short report in an additional patient, all carrying a homozygous G1541A transition (E140K).

RESULTS

The disease onset and symptoms differed significantly from those in compound heterozygotes. MRI and muscle morphology demonstrated an age-dependent progression of disease with predominant involvement of white matter, late appearance of basal ganglia lesions, and neurogenic muscular atrophy in addition to the relatively late onset of hypertrophic cardiomyopathy. The copper uptake of cultured fibroblasts was significantly increased.

CONCLUSIONS

The clinical spectrum of SCO2 deficiency includes the delayed development of hypertrophic obstructive cardiomyopathy and severe neurogenic muscular atrophy. There is increased copper uptake in patients' fibroblasts indicating that the G1541A mutation effects cellular copper metabolism.

Frequency of mitochondrial transfer RNA mutations and deletions in 225 patients presenting with respiratory chain deficiencies

OBJECTIVE

To evaluate the frequency of pathogenic mtDNA transfer RNA mutations and deletions in biochemically demonstrable respiratory chain (RC) deficiencies in paediatric and adult patients.

METHODS

We screened for deletions and sequenced mitochondrial transfer RNA genes in skeletal muscle DNA from 225 index patients with clinical symptoms suggestive of a mitochondrial disorder and with biochemically demonstrable RC deficiency in skeletal muscle.

RESULTS

We found pathogenic mitochondrial DNA mutations in 29% of the patients. The detection rate was significantly higher in adults (48%) than in the paediatric group (18%). Only one pathogenic mutation was detected in the neonatal group. In addition, we describe seven novel transfer RNA sequence variations with unknown pathogenic relevance (six homoplasmic and one heteroplasmic) and 13 homoplasmic polymorphisms. One heteroplasmic transfer RNA(Leu(UUR)) A>G mutation at position 3274 is associated with a distinct neurological syndrome.

CONCLUSIONS

We provide an estimation of the frequency of mitochondrial transfer RNA mutations and deletions in paediatric and adult patients with respiratory chain deficiencies.

The significance of graft-versus-host disease and pretransplantation minimal residual disease status to outcome after allogeneic stem cell transplantation in patients with acute lymphoblastic leukemia

Relapse is the major cause of treatment failure after allogeneic stem cell transplantation (SCT) in patients with acute lymphoblastic leukemia. Minimal residual disease (MRD) was analyzed before SCT in 30 patients with acute lymphoblastic leukemia. The aim was to determine whether the level of MRD before transplantation was correlated with outcome. Fifteen patients were found to have high-level MRD (10(-2) to 10(-3)), 10 had low-level MRD (< 10(-3)), and 5 were MRD(-). Among MRD(-) patients the probability of relapse was 0 in 5, which was less than in MRD(+) patients (13 of 25) (P =.05). No major difference was found between the high- and low-level MRD(+) groups. Among the MRD(+) patients, only 2 of 11 with acute and chronic graft-versus-host disease had a relapse, versus 11 of 14 without (P =.005). In conclusion, for patients entering transplantation while they have residual disease, a combination of acute and chronic graft-versus-host disease may be needed to decrease the risk of relapse after SCT.

Characterization of human muscle type cofilin (CFL2) in normal and regenerating muscle

Cofilins are actin binding proteins and regulate actin assembly in vivo. Numerous cofilin homologues have been characterized in various organisms including mammals. In mice, a ubiquitously expressed cofilin (CFL1) and a skeletal muscle specific cofilin (CFL2) have been described. In the present study, we identified and characterized a human CFL2 gene localized on chromosome 14, with high homology to murine CFL2. Furthermore, we provide evidence for differentially spliced CFL2 transcripts (CFL2a and CFL2b). CFL2b is expressed predominantly in human skeletal muscle and heart, while CFL2a is expressed in various tissues. Genetic defects of CFL2 were excluded for one human muscle disorder, the chromosome 14 linked distal myopathy MPD1, and shown to be only possible to be a rare cause of another, nemaline myopathy. In a mouse model of mechanically induced muscle damage the changes of cofilin expression were monitored during the first 10 days of regeneration, with dephosphorylated CFL2 being the major isoform at later stages of muscle regeneration. A similar predominance of dephosphorylated CFL2 was observed in chronically regenerating dystrophin-deficient muscles of Duchenne muscular dystrophy patients. Therefore, the CFL2 isoform may play an important role in normal muscle function and muscle regeneration.

Multiple origins of the mtDNA 7472insC mutation associated with hearing loss and neurological dysfunction

Several mtDNA mutations have been reported in families with both syndromic and non-syndromic hearing loss. One such mutation is the heteroplasmic 7472insC in the tRNA(Ser(UCN)) gene which has been found in six families, all from Western Europe. However, it was not clear if this distribution was due to a common founder effect or chance sampling of several unrelated families, the 7472insC mutation having occurred multiple times. Haplotype analysis of all six families supports the latter notion. This confirms the pathogenicity of the 7472insC mutation and suggests it may exist in other populations where it may prove to be a small but significant cause of hearing loss, particularly when neurological symptoms are also present.

Wolff-Parkinson-White syndrome and isolated left ventricular abnormal trabeculation as a manifestation of Leber's hereditary optic neuropathy

Myocardial thickening and isolated left ventricular abnormal trabeculation (ILVAT) have not been described in patients with Leber's hereditary optic neuropathy (LHON) before. Wolff-Parkinson-White syndrome, myocardial thickening and ILVAT were found by electrocardiogram, echocardiography and cardiac magnetic resonance imaging in a 48-year-old man with bilateral, severely reduced visual acuity since age 24 years, palpitations since age 43 years and lower limb muscle cramps since age 47 years. Because ILVAT is frequently associated with respiratory chain disorders, neurological investigations were initiated, revealing the primary LHON mutation G3460A in lymphocytic mitochondrial DNA. On the basis of the clinical and genetic data, LHON was diagnosed in the index patient, but also in the patient's brother who showed ILVAT as well. Wolff-Parkinson-White syndrome, myocardial thickening and ILVAT may be rare manifestations of LHON.

Interaction of the G protein beta 3 subunit T825 allele and the IRS-1 Arg972 variant in type 2 diabetes

BACKGROUND

Type 2 diabetes mellitus is a common late-onset disease with a strong genetic component. It is characterized by insulin resistance which results from alterations in insulin signal transduction. The G protein beta 3 subunit 825T allele was recently found to be associated with hypertension and obesity which makes it a sensible candidate gene for type 2 diabetes.

METHODS

In a case-control study on 320 male patients and 962 male healthy controls we investigated the association of two candidate genes with diabetes, i.e. (i) the GNB3 825T allele, associated with a G protein beta 3 subunit splice variant and enhanced intracellular signal transduction, and (ii) the insulin receptor substrate-1 (IRS-1) 972Arg variant, which encodes a protein variant associated with cellular insulin resistance.

RESULTS

The GNB3 825T allele and the IRS-1 972Arg variant were significantly associated with diabetes (odds ratios for either variant 1.4 1.8). Odds ratios were 3 4 in males carrying both alleles.

CONCLUSIONS

The results document an association of a hypertension susceptibility gene with type 2 diabetes which may partially explain the frequent coexistence of both disorders.

Characterization of human SCO1 and COX17 genes in mitochondrial cytochrome-c-oxidase deficiency

At least three proteins, COX17p, SCO1p, and its homologue SCO2p are thought to be involved in mitochondrial copper transport to cytochrome-c-oxidase (COX), the terminal enzyme of the respiratory chain. Recently, we and others have shown that mutations in SCO2 are associated with a lethal infantile hypertrophic cardiomyopathy (HCMP) with COX-deficiency. The majority of patients with a similar phenotype were, however, negative for SCO2 mutations, suggesting the other genes as candidates for this disorder. Here we report on the genomic organization of SCO1 and COX17 on human chromosomes 17 and 3 respectively, and the complete sequence analysis of COX17 and SCO1 in 30 patients with COX deficiency. Using a panel of human:mouse-monochromosomal hybrids, the expression of COX17 was specifically restricted to chromosome 3, indicating that the previously reported sequence on chromosome 13 represents a pseudogene. DNA sequence analysis of SCO1 and COX17 in nine patients with severe COX deficiency and fatal HCMP, and in 21 patients with other COX deficiency disorders, did not reveal any pathogenic mutations or polymorphisms. We conclude that neither SCO1 nor COX17 are common causes of COX deficiency disorders.

A novel mutation in the thiamine responsive megaloblastic anaemia gene SLC19A2 in a patient with deficiency of respiratory chain complex I

The thiamine transporter gene SLC19A2 was recently found to be mutated in thiamine responsive megaloblastic anaemia with diabetes and deafness (TRMA, Rogers syndrome), an early onset autosomal recessive disorder. We now report a novel G1074A transition mutation in exon 4 of the SLC19A2 gene, predicting a Trp358 to ter change, in a girl with consanguineous parents. In addition to the typical triad of Rogers syndrome, the girl presented with short stature, hepatosplenomegaly, retinal degeneration, and a brain MRI lesion. Both muscle and skin biopsies were obtained before high dose thiamine supplementation. While no mitochondrial abnormalities were seen on morphological examination of muscle, biochemical analysis showed a severe deficiency of pyruvate dehydrogenase and complex I of the respiratory chain. In the patient's fibroblasts, the supplementation with high doses of thiamine resulted in restoration of complex I activity. In conclusion, we provide evidence that thiamine deficiency affects complex I activity. The clinical features of TRMA, resembling in part those found in typical mitochondrial disorders with complex I deficiency, may be caused by a secondary defect in mitochondrial energy production.

Mutations in SCO2 are associated with a distinct form of hypertrophic cardiomyopathy and cytochrome c oxidase deficiency

Mutations in SCO2, a cytochrome c oxidase (COX) assembly gene located on chromosome 22, have recently been reported in patients with fatal infantile cardio-encephalomyopathy and severe COX deficiency in heart and skeletal muscle. The Sco2 protein is thought to function as a copper chaperone. To investigate the extent to which mutations in SCO2 are responsible for this phenotype, a complete sequence analysis of the gene was performed on ten patients in nine families. Mutations in SCO2 were found in three patients in two unrelated families. We detected two missense mutations, one of which (G1541A) results in an E140K substitution adjacent to the highly conserved CxxxC metal-binding site. The other (C1634T) results in an R171W substitution more distant from the copper-binding site. A nonsense codon was found on one allele in two siblings presenting with a rapidly progressive fatal cardio-encephalomyopathy. Interestingly, all patients so far reported are compound heterozygotes for the G1541A mutation, suggesting that this is either an ancient allele or a mutational hotspot. The COX deficiency in patient fibroblasts (approximately 50%) did not result in a measurable decrease in the steady-state levels of COX complex polypeptide subunits and could be rescued by transferring chromosome 22, but not other chromosomes. These data indicate that mutations in SCO2 cause a fatal infantile mitochondrial disorder characterized by hypertrophic cardiomyopathy and encephalopathy, and point to the presence of one or more other genes, perhaps in the copper delivery pathway, in this clinical phenotype.

MITOP, the mitochondrial proteome database: 2000 update

MITOP (http://www.mips.biochem.mpg.de/proj/medgen/mitop/) is a comprehensive database for genetic and functional information on both nuclear- and mitochondrial-encoded proteins and their genes. The five species files--Saccharomyces cerevisiae, Mus musculus, Caenorhabditis elegans, Neurospora crassa and Homo sapiens--include annotated data derived from a variety of online resources and the literature. A wide spectrum of search facilities is given in the overlapping sections 'Gene catalogues', 'Protein catalogues', 'Homologies', 'Pathways and metabolism' and 'Human disease catalogue' including extensive references and hyperlinks to other databases. Central features are the results of various homology searches, which should facilitate the investigations into interspecies relationships. Precomputed FASTA searches using all the MITOP yeast protein entries and a list of the best human EST hits with graphical cluster alignments related to the yeast reference sequence are presented. The orthologue tables with cross-listings to all the protein entries for each species in MITOP have been expanded by adding the genomes of Rickettsia prowazeckii and Escherichia coli. To find new mitochondrial proteins the complete yeast genome has been analyzed using the MITOPROT program which identifies mitochondrial targeting sequences. The 'Human disease catalogue' contains tables with a total of 110 human diseases related to mitochondrial protein abnormalities, sorted by clinical criteria and age of onset. MITOP should contribute to the systematic genetic characterization of the mitochondrial proteome in relation to human disease.

Age and cause of death in mitochondrial diseases

We report on the age and the causes of death in 16 patients with mitochondrial diseases. Nine patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) died at a mean age of 34 years and three patients with chronic progressive external ophthalmoplegia at a mean age of 56 years. The causes of death were cardiopulmonary failure (n = 5), status epilepticus (n = 4), aspiration pneumonia (n = 2), pulmonary embolism (n = 2), renal failure (n = 1), metabolic disturbance (n = 1), and unknown causes (n = 1). Thus, many patients in this series died of medical complications, some of which may be prevented.

Mitochondrial disorders. A diagnostic challenge in clinical chemistry

Mitochondria play a pivotal role in cellular metabolism and in energy production in particular. Defects in structure or function of mitochondria, mainly involving the oxidative phosphorylation (OXPHOS), mitochondrial biogenesis and other metabolic pathways, have been shown to be associated with a wide spectrum of clinical phenotypes. The ubiquitous nature of mitochondria and their unique genetic features contribute to the clinical, biochemical and genetic heterogeneity of mitochondrial diseases. We will focus on the recent advances in the field of mitochondrial disorders and their consequences for an advanced clinical and genetic diagnostics. In addition, an overview on recently identified genetic defects and their pathogenic molecular mechanisms will be given.

Different clinical aspects of debrancher deficiency myopathy

OBJECTIVE

To characterise the main clinical phenotypes of debrancher deficiency myopathy and to increase awareness for this probably underdiagnosed disorder.

METHODS

The diagnosis of debrancher deficiency was established by laboratory tests, EMG, and muscle and liver biopsy.

RESULTS

Four patients with debrancher deficiency myopathy were identified in the Tyrol, a federal state of Austria with half a million inhabitants. Clinical appearance was highly variable. The following phenotypes were differentiated: (1) adult onset distal myopathy; (2) subacute myopathy of the respiratory muscles; (3) severe generalised myopathy; and (4) minimal variant myopathy. Exercise intolerance was uncommon. The clinical course was complicated by advanced liver dysfunction in two patients and by severe cardiomyopathy in one. All had raised creatine kinase concentrations (263 to 810 U/l), myogenic and neurogenic features on EMG, and markedly decreased debrancher enzyme activities in muscle or liver biopsy specimens. The findings were substantiated by a review of 79 previously published cases with neuromuscular debrancher deficiency.

CONCLUSIONS

This study illustrates the heterogeneity of neuromuscular manifestations in debrancher deficiency. Based on the clinical appearance, age at onset, and course of disease four phenotypes may be defined which differ in prognosis, frequency of complications, and response to therapy.

Loss-of-function mutations of SURF-1 are specifically associated with Leigh syndrome with cytochrome c oxidase deficiency

Mutations of SURF-1, a gene located on chromosome 9q34, have recently been identified in patients affected by Leigh syndrome (LS), associated with deficiency of cytochrome c oxidase (COX), the terminal component of the mitochondrial respiratory chain. To investigate to what extent SURF-1 is responsible for human disorders because of COX deficiency, we undertook sequence analysis of the SURF-1 gene in 46 unrelated patients. We analyzed 24 COX-defective patients classified as having typical Leigh syndrome (LS(COX)), 6 patients classified as Leigh-like (LL(COX)) cases, and 16 patients classified as non-LS(COX) cases. Frameshift, stop, and splice mutations of SURF-1 were detected in 18 of 24 (75%) of the LS(COX) cases. No mutations were found in the LL(COX) and non-LS(COX) group of patients. Rescue of the COX phenotype was observed in transfected cells from patients harboring SURF-1 mutations, but not in transfected cell lines from 2 patients in whom no mutations were detected by sequence analysis. Loss of function of SURF-1 protein is specifically associated with LS(COX), although a proportion of LS(COX) cases must be the result of abnormalities in genes other than SURF-1. SURF-1 is the first nuclear gene to be consistently mutated in a major category of respiratory chain defects. DNA analysis can now be used to accurately diagnose LS(COX), a common subtype of Leigh syndrome.

MITOP: database for mitochondria-related proteins, genes and diseases

The MITOP database http://websvr.mips.biochem.mpg. de/proj/medgen/mitop/ consolidates information on both nuclear- and mitochondrial-encoded genes and their proteins. The five species files- Saccharomyces cerevisiae, Mus musculus, Caenorhabditis elegans, Neurospora crassa and Homo sapiens -include annotated data derived from a variety of online resources and the literature. A wide spectrum of search facilities is given in the interelated sections 'Gene catalogues', 'Protein catalogues', 'Homologies', 'Pathways and metabolism', and 'Human disease catalogue' including extensive references and hyperlinks for each entry. Precomputed FASTA searches using all the MITOP yeast protein entries and a list of the best EST hits with graphical cluster alignments related to the yeast reference sequence are presented. The MITOP orthologue tables with cross-listing to all the protein entries for each species in the database facilitate investigations into interspecies homology. A program (MITOPROT) is available to identify mitochondrial targeting sequences and graphical depictions of several important mitochondrial processes are included. The 'Human disease catalogue' lists a total of 101 disorders related to mitochondrial protein abnormalities, sorted by clinical criteria and age of onset.

A systematic mutation screen of 10 nuclear and 25 mitochondrial candidate genes in 21 patients with cytochrome c oxidase (COX) deficiency shows tRNA(Ser)(UCN) mutations in a subgroup with syndromal encephalopathy

COX deficiency is believed to be the most common defect in neonates and infants with mitochondrial diseases. To explore the causes of this group of disorders, we examined 25 mitochondrial genes (three COX subunit genes and 22 tRNA genes) and 10 nuclear COX subunit genes for disease associated mutations using PCR-SSCP and direct sequencing of polymorphic SSCP fragments. DNA from one patient with severe COX deficiency and with consanguineous parents was entirely sequenced. The patient population consisted of 21 unrelated index patients with mitochondrial disorders and predominant (n=7) or isolated (n=14) COX deficiency. We detected two distinct tRNA(Ser)(UCN) mutations, which have been recently described in single kindreds, in a subgroup of four patients with COX deficiency, deafness, myoclonic epilepsy, ataxia, and mental retardation. Besides a number of nucleotide variants, a single novel missense mutation, which may contribute to the disease phenotype, was found in the mitochondrial encoded COX 1 gene (G6480A). Mutations in nuclear encoded COX subunit genes were not detected in this study.

Progressive myoclonus epilepsy and mitochondrial myopathy associated with mutations in the tRNA(Ser(UCN)) gene

We report seven unrelated families with mitochondrial tRNA(Ser(UCN)) gene mutations at three different loci. A novel G7497A mutation is found in two families, both of which present with progressive myopathy, ragged-red fibers, lactic acidosis, and deficiency of respiratory chain complexes I and IV. This mutation presumably affects the tertiary tRNA(Ser(UCN)) dihydrouridine interaction. Mutations 7472 insC and T7512C, found in three and two families, respectively, are associated with myoclonus epilepsy, deafness, ataxia, cognitive impairment, and complex IV deficiency. No ragged-red fibers or ultrastructural abnormalities are seen. It is interesting that 6 of our 7 index patients are apparently homoplasmic, indicating a minor pathogenetic power of the tRNA(Ser(UCN)) mutations.

Population genetics and disease susceptibility: characterization of central European haplogroups by mtDNA gene mutations, correlation with D loop variants and association with disease

Mitochondrial (mt)DNA haplogroups in a German control group (n = 67) were characterized by screening mitochondrial coding regions encompassing most of the ND, tRNA and cyt b genes. We used a PCR-SSCP screening approach followed by direct sequencing of polymorphic mtDNA fragments. Five major mtDNA lineages, diverging in at least nine different haplogroups, could be defined by characteristic polymorphic sites in mitochondrial genes. Additional sequencing of two hypervariable segments (HVS-I and II) of the non-coding displacement (D) loop in all control subjects revealed that certain D loop variants were strongly correlated with lineages and haplogroups, while others represented hotspots occurring frequently in different haplogroups. The existence of identified lineages and haplogroups received support from data in the literature, obtained by use of different approaches. Subsequently, we investigated four disease groups for association with these haplogroups: (i) LHON patients (n = 55) carrying at least one of the primary/intermediate LHON mutations at nt 3460, 11778, 14484 and/or 15257; (ii) patients suffering from Wolfram or DIDMOAD syndrome (n = 8); (iii) MELAS patients (n = 9); (iv) a group of children, who died from 'sudden infant death syndrome' (SIDS) (n = 9). The distribution patterns among the haplogroups of the disease groups (LHON, DIDMOAD and SIDS) differed considerably from the control population. LHON and DIDMOAD were significantly under-represented in the most frequent German haplogroup DC, but were concentrated in a mtDNA lineage defined by polymorphisms at nt 4216 + 11251 + 16126. As this lineage diverged into two precisely defined haplogroups, LHON and DIDMOAD could be assigned to the two haplogroups separately. Strikingly, SIDS was often found in association with two rare German haplogroups. MELAS patients were equally distributed among German haplogroups and, moreover, did not reveal any accumulation of specific D loop variants. We conclude that certain European mtDNA haplogroups define a genetic susceptibility basis for various disorders.

Analysis of the mitochondrial DNA from patients with Wolfram (DIDMOAD) syndrome

Wolfram or DIDMOAD (Diabetes Insipidus, Diabetes Mellitus, Optic Atrophy and Deafness) syndrome, which has long been known as an autosomal-recessive disorder, has recently been proposed to be a mitochondrial-mediated disease with either a nuclear or a mitochondrial genetic background. The phenotypic characteristics of the syndrome resemble those found in other mitochondrial (mt)DNA mediated disorders such as Leber's hereditary optic neuropathy (LHON) or maternally inherited diabetes and deafness (MIDD). Therefore, we looked for respective mtDNA alterations in blood samples from 7 patients with DIDMOAD syndrome using SSCP-analysis of PCR-amplified fragments, encompassing all mitochondrial ND and tRNA genes, followed by direct sequencing. Subsequently, we compared mtDNA variants identified in this disease group with those detected in a group of LHON patients (n = 17) and in a group of 69 healthy controls. We found that 4/7 (57%) DIDMOAD patients harbored a specific set of point mutations in tRNA and ND genes including the so-called class II or secondary LHON mutations at nucleotide positions (nps) 4216 and 4917 (haplogroup B). In contrast, LHON-patients were frequently (10/17, 59%) found in association with another cluster of mtDNA variants including the secondary LHON mutations at nps 4216 and 13708 and further mtDNA polymorphisms in ND genes (haplogroup A), overlapping with haplogroup B only by variants at nps 4216 and 11251. The frequencies of both haplogroups were significantly lower in the control group versus the respective disease groups. We propose that haplogroup B represents a susceptibility factor for DIDMOAD which, by interaction with further exogeneous or genetic factors, might increase the risk for disease.

Wolfram (DIDMOAD) syndrome and Leber hereditary optic neuropathy (LHON) are associated with distinct mitochondrial DNA haplotypes

Because Wolfram (or DIDMOAD) syndrome is supposed to be a mitochondrial (mt)-mediated disease, we investigated a group of eight DIDMOAD patients with respect to point mutations of the mtDNA thus far described as being associated with defined mitochondrial disorders such as MELAS, MERRF, and LHON. Furthermore, to screen DIDMOAD patients for other mtDNA defects we used Southern blot analysis to detect mtDNA length mutations and rearrangements as well as PCR-SSCP and direct sequencing to screen all ND genes (complex I of the respiratory chain), the 22 tRNAs, and a part of the cyt b gene for unknown mutations. As a disease control group, 17 LHON patients (harboring one of the primary LHON mutations) were included in this study because of the overlapping clinical symptoms (optic atrophy) in both syndromes. We compared mtDNA variants identified in DIDMOAD patients with those found in LHON patients as well as in a control group consisting of 67 healthy German blood donors. In total, the control group was characterized by 29 polymorphic sites in ND and tRNA genes that define certain major Caucasian haplotypes. We found that a cluster of nucleotide exchanges at nucleotide positions (nps) 4216 and 11,251 roughly discriminates controls (12/67 controls, 18%) from the disease groups (6/8 DIDMOAD patients, 75%; 10/17 LHON patients, 59%). All 4216-positive LHON patients (10 patients) were concentrated in a haplogroup defined by additional exchanges at nps 10,398, 12,612, and 13,708 (haplogroup A), while the bulk of 4216-positive DIDMOAD patients (5 patients) were found in a distinct haplogroup consisting of nucleotide exchanges at nps 4917, 10,463, 13,368, 14,233, and 15,928. The frequencies of both haplogroups were significantly lower in the control group versus the respective disease groups. A more detailed analysis was performed by sequencing the two hypervariable regions of the non-coding D-loop region from patients and controls and corroborated the ranging in the two major haplogroups. Thus, the different clinical features of the mitochondrial disease groups investigated here corresponded to different clusters of mtDNA variants, which might act as predisposing haplotypes, increasing the risk for disease.