Asynchronous Digital Optical Regenerator for 4 x 40 Gbit/s WDM to 160 Gbit/s OTDM Conversion

We propose and numerically analyse an asynchronous digital optical regenerator using a single-EAM loop and a novel neighbor-combine approach. It effectively re-synchronizes input signals with arbitrary phases to the local clock, and regenerates signals with high amplitude fluctuation and polarization mode dispersion. We demonstrate the application of this regenerator for 4x40 Gbit/s WDM to 160 Gbit/s OTDM conversion.

Cardiac manifestations in oxidative phosphorylation disorders of childhood

OBJECTIVE

To determine the frequency, type, and severity of cardiac involvement in pediatric patients with oxidative phosphorylation (OXPHOS) disorders.

STUDY DESIGN

Retrospective review of clinical and laboratory records of all patients with definitive OXPHOS disorders diagnosed and treated at the Royal Children's Hospital in Melbourne between 1984 and 2005.

RESULTS

Of a total of 89 patients (male:female ratio 1.5:1) 29 (33%) had cardiac involvement: 9 as presenting symptoms, 9 developing on follow-up, and 11 with subclinical cardiac findings. Leigh or Leigh-like syndrome and complex I and combined complex I, III, and IV deficiencies were the most common clinical and laboratory diagnoses, respectively. Clinically symptomatic patients had hypertrophic cardiomyopathy (5 patients), dilated cardiomyopathy (4 patients), combined ventricular hypertrophy and systolic dysfunction (3 patients), and left ventricular noncompaction (3 patients) at first assessment. A change in the type of cardiomyopathy was noted on follow-up in 2 patients. Conduction and rhythm abnormalities were present in 7 symptomatic patients.

CONCLUSIONS

Cardiac assessment in children with OXPHOS disorders may reveal subclinical abnormalities of cardiac function. Patients who present with primary cardiac features have a poor prognosis. OXPHOS disorders should be considered in the differential diagnosis of children presenting with otherwise unexplained cardiomyopathy.

Proteins kinases: chromatin-associated enzymes?

Protein kinases contribute to the regulation of gene expression by interacting with transcription factors that are recruited to the regulatory regions of genes. Previous studies investigated the role of protein kinases in transcription initiation. Here, we discuss new insights gleaned from recent work showing that kinases can also interact with chromatin throughout the entire transcribed region of target genes (Pokholok et al., 2006; Proft et al., 2006).

Dosage-dependent transcriptional regulation by the calcineurin/NFAT signaling in developing myocardium transition

Thin spongy myocardium is critical at early embryonic stage [before embryonic day (E) 13.5 in mice] to allow diffusion of oxygen and nutrients to the developing cardiomyocytes. However, establishment of compact myocardium at later stage ( approximately E16.5) during development is necessary to prepare for the increase in demand for blood circulation. Elucidating molecular targets of the spongy-compact myocardium transition between E13.5 and E16.5 in heart development is thus important. Previous studies demonstrated that multiple transcription factors and signaling pathways are involved in the regulation and function of the myocardium in heart development. Disruption of certain transcription factors or critical components of signaling pathways frequently causes structural malformation in heart and persistence of "thin spongy myocardium". We have recently demonstrated activation of the calcineurin/NFAT signaling pathway at E14.5 in developing myocardium. Constitutive inhibition of the calcineurin/NFAT signaling pathway caused embryonic lethality. Molecular targets downstream of the calcineurin/NFAT signaling pathway, however, remains elusive. Here, we report transcription targets, independently and dependently, regulated by the calcineurin/NFAT signaling during the E13.5-E16.5 myocardium transition. We have uncovered that expression of one-third of the induced genes during myocardium transition is calcineurin/NFAT-dependent. Among these calcineurin/NFAT-dependent transcription targets, there is a dosage-dependent regulation. Molecular studies indicate that formation of distinct NFAT:DNA complex, in part, accounts for the dosage-dependent regulation. Thus, in addition to temporal and spatial regulation, dosage-dependent threshold requirement provides another mechanism to modulate transcription response mediated by the calcineurin/NFAT signaling during heart development.

Clinical features and outcomes of childhood dilated cardiomyopathy: results from a national population-based study

BACKGROUND

Despite considerable mortality, population-based prognostic factors for childhood dilated cardiomyopathy are lacking.

METHODS AND RESULTS

A population-based cohort study was undertaken of all children in Australia who presented with cardiomyopathy at age 0 to 10 years between January 1, 1987, and December 31, 1996. A single cardiologist analyzed all cardiac investigations, and a single pathologist analyzed histopathological material. There were 184 subjects with dilated cardiomyopathy. Positive viral identification or lymphocytic myocarditis was found in 30 (68.2%) of 44 cases with available early histology and 8 of 9 cases presenting with sudden death. Freedom from death or transplantation was 72% (95% CI, 65% to 78%) 1 year after presentation and 63% (95% CI, 55% to 70%) at 5 years. By proportional hazards regression analysis, risk factors for death or transplantation comprised age >5 years at presentation (hazard ratio 5.6, 95% CI, 2.6 to 12.0), familial dilated cardiomyopathy (hazard ratio, 2.9; 95% CI, 1.5 to 5.6), lower initial fractional shortening z score (hazard ratio per z-score unit, 0.75; 95% CI, 0.65 to 0.87), and failure to increase fractional shortening z score during follow-up (hazard ratio per unit increase, 0.68; 95% CI, 0.58 to 0.79). At follow-up, 78 (44.6%) of 175 cases diagnosed during life have no symptoms and are not taking any cardiac medication.

CONCLUSIONS

Early mortality is high in childhood dilated cardiomyopathy, but the clinical status of long-term survivors is good. This population-based study identifies children at risk of adverse events.

Nasal Dermoid Sinus Cysts

Nasal dermoid sinus cysts are uncommon congenital anomalies presenting either as cysts or sinuses. They are frequently associated with extension into the intracranial space, requiring craniotomy for adequate resection. At the Royal Children's Hospital in Melbourne, Australia, we have managed 25 patients with nasal dermoid sinus cysts over 8 years and present details of clinical features, preoperative assessment, and surgical management. Six patients presented with infection, including 1 with osteomyelitis. Four of our patients had intracranial extension of their lesions, and all were treated successfully with tailored investigation and appropriate surgical procedures. Insights into diagnosis, investigation, and surgery are offered to facilitate the management of these challenging lesions.

Role of transcription factor NFAT in glucose and insulin homeostasis

Compromised immunoregulation contributes to obesity and complications in metabolic pathogenesis. Here, we demonstrate that the nuclear factor of activated T cell (NFAT) group of transcription factors contributes to glucose and insulin homeostasis. Expression of two members of the NFAT family (NFATc2 and NFATc4) is induced upon adipogenesis and in obese mice. Mice with the Nfatc2-/- Nfatc4-/- compound disruption exhibit defects in fat accumulation and are lean. Nfatc2-/- Nfatc4-/- mice are also protected from diet-induced obesity. Ablation of NFATc2 and NFATc4 increases insulin sensitivity, in part, by sustained activation of the insulin signaling pathway. Nfatc2-/- Nfatc4-/- mice also exhibit an altered adipokine profile, with reduced resistin and leptin levels. Mechanistically, NFAT is recruited to the transcription loci and regulates resistin gene expression upon insulin stimulation. Together, these results establish a role for NFAT in glucose/insulin homeostasis and expand the repertoire of NFAT function to metabolic pathogenesis and adipokine gene transcription.

Optical label switching of DRZ/DPSK orthogonal signal generated by photonic-crystal fiber

We demonstrate orthogonal label switching by using a dark-return-to-zero (DRZ) payload and differential phase-shift keying (DPSK) label generated by a dispersion-flattened photonic-crystal fiber. The high extinction ratio of both the payload and label improves the receiver margin. The DRZ payload introduces little cross talk to the DPSK label due to the RZ-like output of the demodulated DPSK. Simulations are performed to study the eye-closure penalty of the payload and label at different DRZ pulse widths. We compare the DRZ/DPSK with the RZ and DPSK signals numerically at the same data rate and show that the DRZ/DPSK has a strong tolerance to the polarization-mode dispersion. The DRZ/DPSK has a more compact spectrum suitable for the strong filtering requirements in WDM systems.

The circadian clock within the cardiomyocyte is essential for responsiveness of the heart to fatty acids

Cells/organs must respond both rapidly and appropriately to increased fatty acid availability; failure to do so is associated with the development of skeletal muscle and hepatic insulin resistance, pancreatic beta-cell dysfunction, and myocardial contractile dysfunction. Here we tested the hypothesis that the intrinsic circadian clock within the cardiomyocytes of the heart allows rapid and appropriate adaptation of this organ to fatty acids by investigating the following: 1) whether circadian rhythms in fatty acid responsiveness persist in isolated adult rat cardiomyocytes, and 2) whether manipulation of the circadian clock within the heart, either through light/dark (L/D) cycle or genetic disruptions, impairs responsiveness of the heart to fasting in vivo. We report that both the intramyocellular circadian clock and diurnal variations in fatty acid responsiveness observed in the intact rat heart in vivo persist in adult rat cardiomyocytes. Reversal of the 12-h/12-h L/D cycle was associated with a re-entrainment of the circadian clock within the rat heart, which required 5-8 days for completion. Fasting rats resulted in the induction of fatty acid-responsive genes, an effect that was dramatically attenuated 2 days after L/D cycle reversal. Similarly, a targeted disruption of the circadian clock within the heart, through overexpression of a dominant negative CLOCK mutant, severely attenuated induction of myocardial fatty acid-responsive genes during fasting. These studies expose a causal relationship between the circadian clock within the cardiomyocyte with responsiveness of the heart to fatty acids and myocardial triglyceride metabolism.

Nonlinear polarization rotation in a dispersion-flattened photonic-crystal fiber for ultrawideband (>100 nm) all-optical wavelength conversion of 10 Gbit/s nonreturn-to-zero signals

We study the conversion bandwidth of the cross-polarization-modulation (XPoIM)-based wavelength conversion scheme with a dispersion-flattened highly nonlinear photonic-crystal fiber for signals with a nonreturn-to-zero (NRZ) modulation format. Both theoretical and experimental results show that the conversion bandwidth can be extended to cover a very wide band, including S-, C-, and L-bands for 10 Gbit/s NRZ signals (a total bandwidth of 120 nm is experimentally demonstrated). We also study the theoretical bandwidth limit for 40 Gbit/s NRZ signals. A significant extension of the conversion bandwidth using the XPoIM approach compared with the four-wave mixing approach previously reported is demonstrated.

3-bit/symbol optical data format based on simultaneous DRZ, DPSK and PolSK orthogonal modulations

We propose a novel 3-bit/symbol optical data format based on simultaneously modulating dark-return-to-zero (DRZ), differential-phase-shift-keying (DPSK) and polarization-shift-keying (PolSK) on the same optical carrier. Transmission performance is investigated. The proposed data format has a more compact spectrum when compared with other modulation schemes (at the same data rate), such as return-to-zero (RZ), DPSK and PolSK. It is also more tolerant to phase noise when compared with optical-differential-quadrature-phase-shift-keying (ODQPSK).

Clinical isolates of Streptococcus iniae from Asia are more mucoid and β-hemolytic than those from North America

Streptococcus iniae, a widely distributed fish pathogen, is known to cause rare cases of human infection. We describe 2 cases of invasive S. iniae infection, one with septic arthritis complicating chronic gout and the other with bacteremic cellulitis. Both patients were Chinese and have been regularly handling fresh fish for cooking. Both isolates were unidentified or misidentified by 3 commercially available identification system and were only identified by 16S rRNA gene sequencing. When compared with a clinical isolate of S. iniae from Canada, their colonies were larger, more beta-hemolytic, and microcoid. Although bacteremic cellulitis has been described as the most common infection associated with S. iniae, the bacterium has not been reported to cause exacerbations of gouty arthritis previously. Clinical laboratories should be aware of the possibility of different colony morphology of S. iniae from Asia. More accurate identification of nongroupable beta-hemolytic streptococci, especially from patients with epidemiologic linkage to fresh fish, may uncover more cases of S. iniae infection. The Asian population and handlers of fresh fish should be informed of the risk of acquiring S. iniae infection.

Role of the CCAAT/enhancer-binding protein NFATc2 transcription factor cascade in the induction of secretory phospholipase A2

Inflammatory cytokines such as interleukin-1 and tumor necrosis factor-alpha modulate a transcription factor cascade in the liver to induce and sustain an acute and systemic defense against foreign entities. The transcription factors involved include NF-kappaB, STAT, and CCAAT/enhancer-binding protein (C/EBP). Whether the NFAT group of transcription factors (which was first characterized as playing an important role in cytokine gene expression in the adaptive response in immune cells) participates in the acute-phase response in hepatocytes is not known. Here, we have investigated whether NFAT is part of the transcription factor cascade in hepatocytes during inflammatory stress. We report that interleukin-1 or tumor necrosis factor-alpha increases expression of and activates NFATc2. C/EBP-mediated NFATc2 induction is temporally required for expression of type IIA secretory phospholipase A2. NFATc2 is also required for expression of phospholipase D1 and the calcium-binding protein S100A3. Thus, a C/EBP-NFATc2 transcription factor cascade provides an additional means to modulate the acute-phase response upon stimulation with inflammatory cytokines.

URETHRAL POLYPS IN PREPUBERTAL GIRLS

PURPOSE

Urethral polyps in girls are included in the differential diagnosis of interlabial masses. Only 6 cases have been described in the English literature to date and etiology is uncertain. We present 5 more cases and review the literature. We also propose an etiology for urethral polyps in young girls and compare polyps between girls and boys as well as older females.

MATERIALS AND METHODS

The medical records of prepubertal girls with urethral polyps seen at our hospital between 1980 and 2003, including operative reports and followup, were reviewed. A senior pathologist re-inspected the specimens to confirm the diagnosis. A MEDLINE search of urethral polyps was performed.

RESULTS

We identified 5 girls 2 to 10 years old with urethral polyps. All girls presented with "vaginal" bleeding, 1 had recurrent urinary tract infections and vulvitis, 1 had urinary frequency, and 1 had painful voiding. The polyps were not site specific and were located in the distal, mid and proximal urethra. All polyps were excised and were found benign. Four girls were cured after 1 procedure, while in one girl the polyp reappeared. The patients were followed for 1 to 17 years and eventually became asymptomatic.

CONCLUSIONS

Urethral polyps in prepubertal girls are probably benign. We suggest that the etiology of most of polyps in girls is similar to those in older females, that is a prolapsing urothelium that has evolved into a polyp.

Increased chromosome instability but not cancer predisposition in haploinsufficient Bub3 mice

Mitotic spindle checkpoint proteins have been shown to play a crucial role in the accurate segregation of chromosomes during cell division. Bub3 is a member of a group of mitotic checkpoint proteins that are essential for this process. To investigate the role of Bub3 in chromosome segregation and cancer development, we analyzed haploinsufficient cells in mice. Heterozygous Bub3 embryonic fibroblasts displayed increased aneuploidy and premature sister-chromatid separation. In addition, when challenged with the microtubule disruptor nocodazole, the cells showed a slight increase in chromatid breakage and a decrease in the mitotic index. No substantial differences were observed between wild-type and Bub3 heterozygous mice in the frequency or the rate at which tumors appeared. Crossing Bub3(+/-) mice onto a heterozygous tumor-suppressor background of Trp53 or Rb1 similarly revealed no substantial differences in either the number or the rate at which tumors appeared. These results suggest that haploinsufficiency of Bub3 causes a slight increase in chromosome instability but is not clearly associated with a noticeable rise in the probability of tumor formation in the animal, possibly because of a partially functional mitotic checkpoint, or cells exhibiting chromosome instability could have activated the apoptosis pathway and thus escaped tumor induction and detection.

Clinical Features and Outcomes of Childhood Hypertrophic Cardiomyopathy

BACKGROUND

Population-based studies have provided insight into the natural history of adult hypertrophic cardiomyopathy, but comparable information for affected children is lacking.

METHODS AND RESULTS

All Australian children who presented with primary cardiomyopathy at 0 to 10 years of age between January 1, 1987, and December 31, 1996, were enrolled in a longitudinal cohort study. A single cardiologist reviewed serial cardiac investigations on each subject. A total of 80 subjects with hypertrophic cardiomyopathy were identified. An underlying syndromal, genetic, or metabolic condition was identified in 46 subjects (57.5%). There were no cases of sudden death at presentation. Left ventricular outflow tract obstruction was present in 32 subjects (40%); right ventricular outflow obstruction was present in 10 (12.5%). Freedom from death or transplantation was 83% (95% CI, 73 to 90) 5 years after presentation and 76% (95% CI, 62 to 86) 10 years after presentation. By proportional-hazards regression analysis, risk factors for death or transplantation included concentric left ventricular hypertrophy, age at presentation <1 year, lower initial fractional shortening Z score, and increasing left ventricular posterior wall thickness relative to body surface area. At the latest follow-up, 54 of 65 surviving subjects had no symptoms, and 46 were receiving no regular medication.

CONCLUSIONS

Syndromal, genetic, and metabolic causes predominate in children with hypertrophic cardiomyopathy. Ventricular outflow tract obstruction is common. The clinical status of long-term survivors is good. This population-based study identifies children with hypertrophic cardiomyopathy who are at risk of adverse events.

Optical label encoding and swapping using half-bit delayed dark RZ payload and DPSK label

Orthogonal labeling is a potential candidate in future opticallabel- switched-networks. Half-bit-delayed-dark-return-to-zero (HBDDRZ) payload with DPSK orthogonal labeling is proposed. The precise payload extinction-ratio adjustment at source nodes and maintenance at each intermediate node is not needed. The high extinction-ratio of both payload and label improves the receiver margin. Owing to the RZ-like nature of the demodulated DPSK label, HBDDRZ payload causes negligible effect on the label. Nonlinear-optical-loop-mirror generates the HBDDRZ payload, which is then encoded by DPSK label. Label swapping is demonstrated by birefringence switching. 10-Gb/s bit-error-rate measurements are performed.

Recruitment of the extracellular signal-regulated kinase/ribosomal S6 kinase signaling pathway to the NFATc4 transcription activation complex

Integration of protein kinases into transcription activation complexes influences the magnitude of gene expression. The nuclear factor of activated T cells (NFAT) group of proteins are critical transcription factors that direct gene expression in immune and nonimmune cells. A balance of phosphotransferase activity is necessary for optimal NFAT activation. Activation of NFAT requires dephosphorylation by the calcium-mediated calcineurin phosphatase to promote NFAT nuclear accumulation, and the Ras-activated extracellular signal-regulated kinase (ERK) mitogen-activated protein (MAP) kinase, which targets NFAT partners, to potentiate transcription. Whether protein kinases operate on NFAT and contribute positively to transcription activation is not clear. Here, we coupled DNA affinity isolation with in-gel kinase assays to avidly pull down the activated NFAT and identify its associated protein kinases. We demonstrate that p90 ribosomal S6 kinase (RSK) is recruited to the NFAT-DNA transcription complex upon activation. The formation of RSK-NFATc4-DNA transcription complex is also apparent upon adipogenesis. Bound RSK phosphorylates Ser(676) and potentiates NFATc4 DNA binding by escalating NFAT-DNA association. Ser(676) is also targeted by the ERK MAP kinase, which interacts with NFAT at a distinct region than RSK. Thus, integration of the ERK/RSK signaling pathway provides a mechanism to modulate NFATc4 transcription activity.

Severe fetal brain dysgenesis with focal calcification

OBJECTIVE

To describe a fetal syndrome of abnormal brain development with intracranial calcification, identified in three successive pregnancies.

METHODS

Clinical, imaging, and pathological descriptions, and pedigree assessment.

RESULTS

All three affected pregnancies were terminated, following imaging diagnosis of brain abnormality. The most complete fetal study, from the third of these pregnancies, showed widespread foci of brain calcification not associated with inflammation, with extensive necrosis and calcification of periventricular white matter, but with sparing of thalamus and basal ganglia. The corticospinal tracts were severely hypoplastic.

CONCLUSION

This condition appears to be a 'new' genetically determined, probably autosomal recessive disorder of severe early brain dysgenesis with focal calcification, resembling, but distinct from, certain other clinical genetic entities of which brain calcification is a part.

Respiratory chain enzyme analysis in muscle and liver

Respiratory Chain (RC) enzyme analysis remains the mainstay for diagnosis of children suspected of having a RC disorder. A previous international workshop suggested a set of criteria for the ideal approach to diagnosis but concluded that probably no single centre fulfilled all these criteria. Major practical issues relate to the range of tissues tested, whether frozen tissue biopsies can be used reliably, assay methods, difficulty in defining realistic reference ranges, and the lack of an external quality assurance scheme. We discuss these issues and describe our experience over the last decade with assaying RC enzymes in over 600 skeletal muscle and 300 liver biopsies from patients, a range of different controls (other known inborn errors, end-stage liver disease, post-mortem samples) and single donated normal muscle and liver samples assayed on more than 100 occasions over 5- to 10-year periods. Our experience is that 'sick' tissues have wider 'normal' ranges than 'healthy' tissues. Caution is therefore needed to ensure that secondary RC defects are not misdiagnosed as primary RC defects. We describe diagnostic criteria that integrate the results of RC enzyme assays with clinical, histological, metabolic and molecular investigations to determine whether the overall diagnostic certainty is possible, probable or definite.

Optical packet labeling based on simultaneous polarization shift keying and amplitude shift keying

We propose and demonstrate label encoding-swapping and transmission for an orthogonally labeled packet by use of a 10-Gbit/s amplitude shift keying payload and a 2.5-Gbit/s polarization shift keying (PolSK) label. A simple scheme for demodulating and demultiplexing the PolSK label based on an injection-locked Fabry-Perot laser diode is described. The extinction ratio of the newly added PolSK label can be precisely controlled and maintained after the intermediate node.

Ovarian lesions in children and adolescents--an 11-year review

OBJECTIVE

To describe the spectrum of pediatric ovarian pathology, identifying the clinical features and ultrasound characteristics that help in decisions about patient management, and to correlate these with ovarian pathology.

PATIENTS AND METHODS

Retrospective analysis of 134 records of patients admitted with ovarian lesions to Royal Children's Hospital, Melbourne over an 11-year period (1989-99 inclusive).

RESULTS

The age of presentation varied widely from 2 days to 19 years with 63.4% being over 12 years of age. Eighty-one patients (60.4%) had physiological or functional ovarian cysts, 52 of which required surgical intervention. Forty-four patients (32.8%) had neoplastic lesions and a palpable abdominal mass was felt in 53.7% of them. Mature cystic teratoma or dermoid cyst, seen in 27 patients, was the commonest neoplasm, and 77.8% of these children were under 12 years. Six children had malignant ovarian neoplasms, of which five were germ cell in origin. Five patients had epithelial or stromal neoplastic lesions. Endocrine manifestations were seen in seven patients and included early or precocious puberty and virilization. Plain trans-abdominal ultrasonography was useful in identifying ovarian lesions in 94 (81.7%) of the 115 patients in whom it was performed, but was not helpful in determining the nature of the lesion. Neoplastic ovarian lesions were commonly greater than 10 cm in diameter

CONCLUSIONS

Physiological or functional ovarian cysts are the most common ovarian lesions seen in the pediatric age group and malignant neoplasms are rare. A palpable abdominal mass or ovarian lesion >10 cm was significantly associated with the lesion being neoplastic. Lesions <5 cm in post-pubertal girls were significantly more likely to be non-neoplastic. Ultrasonography is useful in localizing ovarian lesions but is not helpful in determining their pathological nature. Endocrine manifestations sometimes occur with either benign or malignant lesions of the ovary.

Cholinergic transmission to colonic circular muscle of children with slow-transit constipation is unimpaired, but transmission via NK2 receptors is lacking

Tachykinins (TKs) colocalize with acetylcholine in excitatory motor neurones supplying human colonic circular muscle (CCM). Some children with slow-transit constipation (STC) have reduced TK-immunoreactivity in nerve terminals in CCM suggesting a deficit in neuromuscular transmission. This study aimed to test this possibility. Seromuscular biopsies of transverse colon were obtained laparoscopically from STC children (37, 17 with low density of TK-immunoreactivity). Specimens of transverse (17) and sigmoid colon (20) were obtained from adults undergoing colonic resection for cancer. CCM contractions were measured isotonically and responses to carbachol, neurokinin A (NKA) and electrical field stimulation (EFS) recorded. Carbachol and NKA-evoked contractions in adult and STC colon. Hyoscine (2 micromol L-1) significantly depressed responses to EFS in all preparations. Blockade of NK2 receptors (SR 48968, 2 micromol L-1) significantly depressed EFS-evoked contractions of adult transverse CCM, but had no effect on STC preparations. Thus, neuromuscular transmission in both adults and STC children is predominantly cholinergic and this component is unimpaired in the latter, indicating that reduced TK-immunoreactivity is not a marker for depressed cholinergic responses. Although pharmacologically responsive TK receptors are present in STC colon, we did not detect neuromuscular transmission mediated by release of TKs in these preparations.

Low mutant load of mitochondrial DNA G13513A mutation can cause Leigh's disease

Respiratory chain complex I deficiency is a common cause of Leigh's disease (LD) and can be caused by mutations in genes encoded by either nuclear or mitochondrial DNA (mtDNA). Most pathogenic mtDNA mutations act recessively and only cause disease when present at high mutant loads (typically >90%) in tissues such as muscle and brain. Two mitochondrial DNA mutations in complex I subunit genes, G14459A in ND6, and T12706C in ND5, have been associated with complex I deficiency and LD. We report another ND5 mutation, G13513A, in three unrelated patients with complex I deficiency and LD. The G13513A mutation was present at mutant loads of approximately 50% or less in all tissues tested, including multiple brain regions. The threshold mutant load for causing a complex I defect in cultured cells was approximately 30%. Blue Native polyacrylamide gel electrophoresis showed that fibroblasts with 45% G13513A mutant load had approximately 50% of the normal amount of fully assembled complex I. Fibroblasts with greater than 97% of the ND6 G14459A mutation had only 20% fully assembled complex I, suggesting that both mutations disrupt complex I assembly or turnover. We conclude that the G13513A mutation causes a complex I defect when present at unusually low mutant load and may act dominantly.