Mitochondrial tRNA(Leu(UUR)) mutation m.3302A > G presenting as childhood-onset severe myopathy: threshold determination through segregation study

Mitochondrial tRNA(Leu(UUR)) mutation m.3302A > G is associated with respiratory chain complex I deficiency and has been described as a rare cause of mostly adult-onset slowly progressive myopathy. Five families with 11 patients have been described so far; 5 of them died young due to cardiorespiratory failure. Here, we report on a segregation study in a family with an index patient who already presented at the age of 18 months with proximal muscular hypotonia, abnormal fatigability, and lactic acidosis. This early-onset myopathy was rapidly progressive. At 8 years, the patient is wheel-chair bound, requires nocturnal assisted ventilation, and suffers from recurrent respiratory infections. Severe complex I deficiency and nearly homoplasmy for m.3302A > G were found in muscle. We collected blood, hair, buccal swabs and muscle biopsies from asymptomatic adults in this pedigree and determined heteroplasmy levels in these tissues as well as OXPHOS activities in muscle. All participating asymptomatic adults had normal OXPHOS activities. In contrast to earlier reports, we found surprisingly little variation of heteroplasmy levels in different tissues of the same individual. Up to 45% mutation load in muscle and up to 38% mutation load in other tissues were found in non-affected adults. The phenotypic spectrum of tRNA(Leu(UUR)) m.3302A > G mutation seems to be wider than previously described. A threshold of more than 45% heteroplasmy in muscle seems to be necessary to alter complex I activity leading to clinical manifestation. The presented data may be helpful for prognostic considerations and counseling in affected families.

The prognostic significance of cytogenetic aberrations in childhood acute myeloid leukaemia. A study of the Swiss Paediatric Oncology Group (SPOG)

In childhood-onset acute myeloid leukaemia (AML) the clinical value of karyotypic aberrations is now acknowledged, although there is still debate concerning the prognostic significance of some events. To add to this knowledge, cytogenetic analysis was performed on a consecutive series of 84 childhood AML patients diagnosed in Switzerland. A result was obtained for all patients, with 69 (82%) showing a clonal karyotypic aberration. In the remaining 15 (18%), no karyotypic aberration was seen by either conventional or fluorescence in situ hybridisation analyses. The most frequent aberrations observed were t(11q23) (19% of all patients), t(8;21) (12%) and +8 (11%). Except for cytogenetics, no clinical parameter was shown to be significantly associated with outcome. The analysis of individual cytogenetic subgroups demonstrated that aberrations involving chromosome 16q were the strongest predictor of a good prognosis, while +8 and complex karyotypes represented the strongest predictors of a poor prognosis. It was also noteworthy that patients with the rare aberrations of del(11q) (n = 4) and t(16;21)(p11;q22) (n = 3) had a poor outcome. The results support the importance of cytogenetic analysis in childhood AML, but show that further work is required in the classification of the poor prognosis aberrations.

Mitochondrial dysfunction and Purkinje cell loss in autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS)

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a childhood-onset neurological disease resulting from mutations in the SACS gene encoding sacsin, a 4,579-aa protein of unknown function. Originally identified as a founder disease in Québec, ARSACS is now recognized worldwide. Prominent features include pyramidal spasticity and cerebellar ataxia, but the underlying pathology and pathophysiological mechanisms are unknown. We have generated an animal model for ARSACS, sacsin knockout mice, that display age-dependent neurodegeneration of cerebellar Purkinje cells. To explore the pathophysiological basis for this observation, we examined the cell biological properties of sacsin. We show that sacsin localizes to mitochondria in non-neuronal cells and primary neurons and that it interacts with dynamin-related protein 1, which participates in mitochondrial fission. Fibroblasts from ARSACS patients show a hyperfused mitochondrial network, consistent with defects in mitochondrial fission. Sacsin knockdown leads to an overly interconnected and functionally impaired mitochondrial network, and mitochondria accumulate in the soma and proximal dendrites of sacsin knockdown neurons. Disruption of mitochondrial transport into dendrites has been shown to lead to abnormal dendritic morphology, and we observe striking alterations in the organization of dendritic fields in the cerebellum of knockout mice that precedes Purkinje cell death. Our data identifies mitochondrial dysfunction/mislocalization as the likely cellular basis for ARSACS and indicates a role for sacsin in regulation of mitochondrial dynamics.

Novel mutations consolidate KCTD7 as a progressive myoclonus epilepsy gene

The progressive myoclonus epilepsies (PMEs) comprise a group of clinically and genetically heterogeneous disorders characterised by myoclonus, epilepsy, and neurological deterioration. This study aimed to identify the underlying gene(s) in childhood onset PME patients with unknown molecular genetic background.

Study of a Swiss dopa-responsive dystonia family with a deletion in GCH1: redefining DYT14 as DYT5

OBJECTIVE: To report the study of a multigenerational Swiss family with dopa-responsive dystonia (DRD). METHODS: Clinical investigation was made of available family members, including historical and chart reviews. Subject examinations were video recorded. Genetic analysis included a genome-wide linkage study with microsatellite markers (STR), GTP cyclohydrolase I (GCH1) gene sequencing, and dosage analysis. RESULTS: We evaluated 32 individuals, of whom 6 were clinically diagnosed with DRD, with childhood-onset progressive foot dystonia, later generalizing, followed by parkinsonism in the two older patients. The response to levodopa was very good. Two additional patients had late onset dopa-responsive parkinsonism. Three other subjects had DRD symptoms on historical grounds. We found suggestive linkage to the previously reported DYT14 locus, which excluded GCH1. However, further study with more stringent criteria for disease status attribution showed linkage to a larger region, which included GCH1. No mutation was found in GCH1 by gene sequencing but dosage methods identified a novel heterozygous deletion of exons 3 to 6 of GCH1. The mutation was found in seven subjects. One of the patients with dystonia represented a phenocopy. CONCLUSIONS: This study rules out the previously reported DYT14 locus as a cause of disease, as a novel multiexonic deletion was identified in GCH1. This work highlights the necessity of an accurate clinical diagnosis in linkage studies as well as the need for appropriate allele frequencies, penetrance, and phenocopy estimates. Comprehensive sequencing and dosage analysis of known genes is recommended prior to genome-wide linkage analysis.

Exploring the genetic link between RLS and ADHD

Attention deficit/hyperactivity disorder (ADHD) is a highly heritable neurodevelopmental disorder of childhood onset. Clinical and biological evidence points to shared common central nervous system (CNS) pathology of ADHD and restless legs syndrome (RLS). It was hypothesized that variants previously found to be associated with RLS in two large genome-wide association studies (GWA), will also be associated with ADHD. SNPs located in MEIS1 (rs2300478), BTBD9 (rs9296249, rs3923809, rs6923737), and MAP2K5 (rs12593813, rs4489954) as well as three SNPs tagging the identified haplotype in MEIS1 (rs6710341, rs12469063, rs4544423) were genotyped in a well characterized German sample of 224 families comprising one or more affected sibs (386 children) and both parents. We found no evidence for preferential transmission of the hypothesized variants to ADHD. Subsequent analyses elicited nominal significant association with haplotypes consisting of the three SNPs in BTBD9 (chi2 = 14.8, df = 7, nominal p = 0.039). According to exploratory post hoc analyses, the major contribution to this finding came from the A-A-A-haplotype with a haplotype-wise nominal p-value of 0.009. However, this result did not withstand correction for multiple testing. In view of our results, RLS risk alleles may have a lower effect on ADHD than on RLS or may not be involved in ADHD. The negative findings may additionally result from genetic heterogeneity of ADHD, i.e. risk alleles for RLS may only be relevant for certain subtypes of ADHD. Genes relevant to RLS remain interesting candidates for ADHD; particularly BTBD9 needs further study, as it has been related to iron storage, a potential pathophysiological link between RLS and certain subtypes of ADHD.

Phenotypes of childhood asthma: are they real?

It has been suggested that there are several distinct phenotypes of childhood asthma or childhood wheezing. Here, we review the research relating to these phenotypes, with a focus on the methods used to define and validate them. Childhood wheezing disorders manifest themselves in a range of observable (phenotypic) features such as lung function, bronchial responsiveness, atopy and a highly variable time course (prognosis). The underlying causes are not sufficiently understood to define disease entities based on aetiology. Nevertheless, there is a need for a classification that would (i) facilitate research into aetiology and pathophysiology, (ii) allow targeted treatment and preventive measures and (iii) improve the prediction of long-term outcome. Classical attempts to define phenotypes have been one-dimensional, relying on few or single features such as triggers (exclusive viral wheeze vs. multiple trigger wheeze) or time course (early transient wheeze, persistent and late onset wheeze). These definitions are simple but essentially subjective. Recently, a multi-dimensional approach has been adopted. This approach is based on a wide range of features and relies on multivariate methods such as cluster or latent class analysis. Phenotypes identified in this manner are more complex but arguably more objective. Although phenotypes have an undisputed standing in current research on childhood asthma and wheezing, there is confusion about the meaning of the term 'phenotype' causing much circular debate. If phenotypes are meant to represent 'real' underlying disease entities rather than superficial features, there is a need for validation and harmonization of definitions. The multi-dimensional approach allows validation by replication across different populations and may contribute to a more reliable classification of childhood wheezing disorders and to improved precision of research relying on phenotype recognition, particularly in genetics. Ultimately, the underlying pathophysiology and aetiology will need to be understood to properly characterize the diseases causing recurrent wheeze in children.

Routine vaccination against pertussis and the risk of childhood asthma: a population-based cohort study

BACKGROUND: In industrialized countries vaccination coverage remains suboptimal, partly because of perception of an increased risk of asthma. Epidemiologic studies of the association between childhood vaccinations and asthma have provided conflicting results, possibly for methodologic reasons such as unreliable vaccination data, biased reporting, and reverse causation. A recent review stressed the need for additional, adequately controlled large-scale studies. OBJECTIVE: Our goal was to determine if routine childhood vaccination against pertussis was associated with subsequent development of childhood wheezing disorders and asthma in a large population-based cohort study. METHODS: In 6811 children from the general population born between 1993 and 1997 in Leicestershire, United Kingdom, respiratory symptom data from repeated questionnaire surveys up to 2003 were linked to independently collected vaccination data from the National Health Service database. We compared incident wheeze and asthma between children of different vaccination status (complete, partial, and no vaccination against pertussis) by computing hazard ratios. Analyses were based on 6048 children, 23 201 person-years of follow-up, and 2426 cases of new-onset wheeze. RESULTS: There was no evidence for an increased risk of wheeze or asthma in children vaccinated against pertussis compared with nonvaccinated children. Adjusted hazard ratios comparing fully and partially vaccinated with nonvaccinated children were close to one for both incident wheeze and asthma. CONCLUSION: This study provides no evidence of an association between vaccination against pertussis in infancy and an increased risk of later wheeze or asthma and does not support claims that vaccination against pertussis might significantly increase the risk of childhood asthma.

Comparison of phenotypes of childhood wheeze and cough in 2 independent cohorts

BACKGROUND Among children with wheeze and recurrent cough there is great variation in clinical presentation and time course of the disease. We previously distinguished 5 phenotypes of wheeze and cough in early childhood by applying latent class analysis to longitudinal data from a population-based cohort (original cohort). OBJECTIVE To validate previously identified phenotypes of childhood cough and wheeze in an independent cohort. METHODS We included 903 children reporting wheeze or recurrent cough from an independent population-based cohort (validation cohort). As in the original cohort, we used latent class analysis to identify phenotypes on the basis of symptoms of wheeze and cough at 2 time points (preschool and school age) and objective measurements of atopy, lung function, and airway responsiveness (school age). Prognostic outcomes (wheeze, bronchodilator use, cough apart from colds) 5 years later were compared across phenotypes. RESULTS When using a 5-phenotype model, the analysis distinguished 3 phenotypes of wheeze and 2 of cough as in the original cohort. Two phenotypes were closely similar in both cohorts: Atopic persistent wheeze (persistent multiple trigger wheeze and chronic cough, atopy and reduced lung function, poor prognosis) and transient viral wheeze (early-onset transient wheeze with viral triggers, favorable prognosis). The other phenotypes differed more between cohorts. These differences might be explained by differences in age at measurements. CONCLUSIONS Applying the same method to 2 different cohorts, we consistently identified 2 phenotypes of wheeze (atopic persistent wheeze, transient viral wheeze), suggesting that these represent distinct disease processes. Differences found in other phenotypes suggest that the age when features are assessed is critical and should be considered carefully when defining phenotypes.

Clinical manifestation of Fuchs uveitis syndrome in childhood

PURPOSE The aim of this study was to describe clinical signs and complications of Fuchs uveitis syndrome (FUS) with onset in childhood. METHODS Ophthalmologic findings and complications in patients with FUS becoming manifest before the age of 16 years were analyzed in a retrospective study at a tertiary referral uveitis center. Inclusion criteria were the presence of pathognomonic FUS findings at any time point and exclusion of any systemic immune-mediated or infectious disease. RESULTS A total of 23 patients (male = 16, female = 7) with juvenile FUS (unilateral n = 20, bilateral n = 3 patients) were included in the study. Mean ages at uveitis and FUS diagnosis were 12.0 ± 4.2 and 22.7 ± 10.7 years, respectively. In six patients, inflammation was noted at age ≤ 7 years. The following inflammatory signs were observed in a total of 26 eyes: ≤ 1+ anterior chamber cell grade (n = 26), vitreous cells (n = 24), fine keratic precipitates (KPs; n = 23), stellate KPs (n = 11), mutton-fat KPs (n = 23), diffuse (n = 24) or inferior (n = 8) distribution of KPs, Koeppe nodules (n = 10), and iris heterochromia (n = 14). A representative subgroup of patients (n = 5) is shown who presented with non-specific clinical signs in the beginning and in whom typical FUS signs became manifest only at a later stage. Secondary complications such as cataract (n = 19), ocular hypertension (n = 3), or glaucomatous disc damage (n = 2) were found after a mean uveitis duration of 11.6, 19.5, and 20.3 years, respectively. CONCLUSION FUS may begin in early childhood, and the characteristic findings may not be present at onset of disease. The diagnosis is often delayed for years, occasionally with the consequence of overtreatment with anti-inflammatory drugs.