Atle Melberg

CSF hypocretin/orexin levels in narcolepsy and other neurological conditions

Objective: To examine the specificity of low CSF hypocretin-1 levels in narcolepsy and explore the potential role of hypocretins in other neurologic disorders. Methods: A method to measure hypocretin-1 in 100 μL of crude CSF sample was established and validated. CSF hypocretin-1 was measured in 42 narcolepsy patients (ages 16–70 years), 48 healthy controls (ages 22–77 years,) and 235 patients with various other neurologic conditions (ages 0–85 years). Results: As previously reported, CSF hypocretin-1 levels were undetectably low (<100 pg/mL) in 37 of 42 narcolepsy subjects. Hypocretin-1 levels were detectable in all controls (224–653 pg/mL) and all neurologic patients (117–720 pg/mL), with the exception of three patients with Guillain–Barré syndrome (GBS). Hypocretin-1 was within the control range in most neurologic patients tested, including patients with AD, PD, and MS. Low but detectable levels (100–194 pg/mL) were found in a subset of patients with acute lymphocytic leukemia, intracranial tumors, craniocerebral trauma, CNS infections, and GBS. Conclusions: Undetectable CSF hypocretin-1 levels are highly specific to narcolepsy and rare cases of GBS. Measuring hypocretin-1 levels in the CSF of patients suspected of narcolepsy is a useful diagnostic procedure. Low hypocretin levels are also observed in a large range of neurologic conditions, most strikingly in subjects with head trauma. These alterations may reflect focal lesions in the hypothalamus, destruction of the blood brain barrier, or transient or chronic hypofunction of the hypothalamus. Future research in this area is needed to establish functional significance.

Mutations in DNMT1 cause autosomal dominant cerebellar ataxia, deafness and narcolepsy

Autosomal dominant cerebellar ataxia, deafness and narcolepsy (ADCA-DN) is characterized by late onset (30-40 years old) cerebellar ataxia, sensory neuronal deafness, narcolepsy-cataplexy and dementia. We performed exome sequencing in five individuals from three ADCA-DN kindreds and identified DNMT1 as the only gene with mutations found in all five affected individuals. Sanger sequencing confirmed the de novo mutation p.Ala570Val in one family, and showed co-segregation of p.Val606Phe and p.Ala570Val, with the ADCA-DN phenotype, in two other kindreds. An additional ADCA-DN kindred with a p.GLY605Ala mutation was subsequently identified. Narcolepsy and deafness were the first symptoms to appear in all pedigrees, followed by ataxia. DNMT1 is a widely expressed DNA methyltransferase maintaining methylation patterns in development, and mediating transcriptional repression by direct binding to HDAC2. It is also highly expressed in immune cells and required for the differentiation of CD4+ into T regulatory cells. Mutations in exon 20 of this gene were recently reported to cause hereditary sensory neuropathy with dementia and hearing loss (HSAN1). Our mutations are all located in exon 21 and in very close spatial proximity, suggesting distinct phenotypes depending on mutation location within this gene.

Childhood epilepsy, familial hemiplegic migraine, cerebellar ataxia, and a new CACNA1A mutation.

The CACNA1A gene encodes the pore-forming subunit of neuronal P/Q type Ca2+ channels. Mutations in this gene cause a spectrum of neurologic diseases, including familial hemiplegic migraine (FHM) with or without ataxia.1 We report a novel de novo CACNA1A mutation in a Swedish family. Three mutation carriers had FHM and early onset ataxia; additional childhood epilepsy occurred in two . The proband, II-3, is a 54-year-old woman with slowly progressive cerebellar ataxia since childhood and cerebellar atrophy on CT. She was hospitalized at ages 7 and 8 because of decreased consciousness and vomiting for 1 day, starting with a lucid interval after a fall. She experienced four hemiplegic migraine attacks between ages 14 and 30 years and weekly at age 47. Seizures were never observed. Her 32-year-old son (III-5) and 30-year-old daughter (III-6), who have different fathers, showed cerebellar ataxia at age 4. Ataxia is now prominent in both, and brain imaging shows cerebellar atrophy. …

POLG1 Mutations Associated With Progressive Encephalopathy in Childhood

Abstract We have identified compound heterozygous missense mutations in POLG1, encoding the mitochondrial DNA polymerase gamma (Pol &ggr;), in 7 children with progressive encephalopathy from 5 unrelated families. The clinical features in 6 of the children included psychomotor regression, refractory seizures, stroke-like episodes, hepatopathy, and ataxia compatible with Alpers-Huttenlocher syndrome. Three families harbored a previously reported A467T substitution, which was found in compound with the earlier described G848S or the W748S substitution or a novel R574W substitution. Two families harbored the W748S change in compound with either of 2 novel mutations predicted to give an R232H or M1163R substitution. Muscle morphology showed mitochondrial myopathy with cytochrome c oxidase (COX)-deficient fibers in 4 patients. mtDNA analyses in muscle tissue revealed mtDNA depletion in 3 of the children and mtDNA deletions in the 2 sibling pairs. Neuropathologic investigation in 3 children revealed widespread cortical degeneration with gliosis and subcortical neuronal loss, especially in the thalamus, whereas there were only subcortical neurodegenerative findings in another child. The results support the concept that deletions as well as depletion of mtDNA are involved in the pathogenesis of Alpers-Huttenlocher syndrome and add 3 new POLG1 mutations associated with an early-onset neurodegenerative disease.

Hereditary myopathy with early respiratory failure associated with a mutation in A-band titin

Hereditary myopathy with early respiratory failure and extensive myofibrillar lesions has been described in sporadic and familial cases and linked to various chromosomal regions. The mutated gene is unknown in most cases. We studied eight individuals, from three apparently unrelated families, with clinical and pathological features of hereditary myopathy with early respiratory failure. The investigations included clinical examination, muscle histopathology and genetic analysis by whole exome sequencing and single nucleotide polymorphism arrays. All patients had adult onset muscle weakness in the pelvic girdle, neck flexors, respiratory and trunk muscles, and the majority had prominent calf hypertrophy. Examination of pulmonary function showed decreased vital capacity. No signs of cardiac muscle involvement were found. Muscle histopathological features included marked muscle fibre size variation, fibre splitting, numerous internal nuclei and fatty infiltration. Frequent groups of fibres showed eosinophilic inclusions and deposits. At the ultrastructural level, there were extensive myofibrillar lesions with marked Z-disc alterations. Whole exome sequencing in four individuals from one family revealed a missense mutation, g.274375T>C; p.Cys30071Arg, in the titin gene (TTN). The mutation, which changes a highly conserved residue in the myosin binding A-band titin, was demonstrated to segregate with the disease in all three families. High density single nucleotide polymorphism arrays covering the entire genome demonstrated sharing of a 6.99 Mb haplotype, located in chromosome region 2q31 including TTN, indicating common ancestry. Our results demonstrate a novel and the first disease-causing mutation in A-band titin associated with hereditary myopathy with early respiratory failure. The typical histopathological features with prominent myofibrillar lesions and inclusions in muscle and respiratory failure early in the clinical course should be incentives for analysis of TTN mutations.

Clinical manifestation and a new ISCU mutation in iron–sulphur cluster deficiency myopathy

Myopathy with deficiency of succinate dehydrogenase and aconitase is a recessively inherited disorder characterized by childhood-onset early fatigue, dyspnoea and palpitations on trivial exercise. The disease is non-progressive, but life-threatening episodes of widespread weakness, severe metabolic acidosis and rhabdomyolysis may occur. The disease has so far only been identified in northern Sweden. The clinical, histochemical and biochemical phenotype is very homogenous and the patients are homozygous for a deep intronic IVS5 + 382G>C splicing affecting mutation in ISCU, which encodes the differently spliced cytosolic and mitochondrial iron-sulphur cluster assembly protein IscU. Iron-sulphur cluster containing proteins are essential for iron homeostasis and respiratory chain function, with IscU being among the most conserved proteins in evolution. We identified a shared homozygous segment of only 405,000 base pair with the deep intronic mutation in eight patients with a phenotype consistent with the original description of the disease. Two other patients, two brothers, had an identical biochemical and histochemical phenotype which is probably pathognomonic for muscle iron-sulphur cluster deficiency, but they presented with a disease where the clinical phenotype was characterized by early onset of a slowly progressive severe muscle weakness, severe exercise intolerance and cardiomyopathy. The brothers were compound heterozygous for the deep intronic mutation and had a c.149 G>A missense mutation in exon 3 changing a completely conserved glycine residue to a glutamate. The missense mutation was inherited from their mother who was of Finnish descent. The intronic mutation affects mRNA splicing and results in inclusion of pseudoexons in most transcripts in muscle. The pseudoexon inclusion results in a change in the reading frame and appearance of a premature stop codon. In western blot analysis of protein extracts from fibroblasts, there was no pronounced reduction of IscU in any of the patients, but the analysis revealed that the species corresponding to mitochondrial IscU migrates slower than a species present only in whole cells. In protein extracted from isolated skeletal muscle mitochondria the western blot analysis revealed a severe deficiency of IscU in the homozygous patients and appearance of a faint new fraction that could represent a truncated protein. There was only a slight reduction of mitochondrial IscU in the compound heterozygotes, despite their severe phenotype, indicating that the IscU expressed in these patients is non-functional.

Welander Distal Myopathy Caused by an Ancient Founder Mutation in TIA1 Associated with Perturbed Splicing.

Welander distal myopathy (WDM) is an adult onset autosomal dominant disorder characterized by distal limb weakness, which progresses slowly from the fifth decade. All WDM patients are of Swedish or Finnish descent and share a rare chromosome 2p13 haplotype. We restricted the WDM‐associated haplotype followed by whole exome sequencing. Within the conserved haplotype, we identified a single heterozygous mutation c.1150G>A (p.E384K) in T‐cell intracellular antigen‐1 (TIA1) in all WDM patients investigated (n = 43). The TIA1 protein regulates splicing, and translation through direct interaction with mRNA and the p.E384K mutation is located in the C‐terminal Q‐rich domain that interacts with the U1‐C splicing factor. TIA1 has been shown to prevent skipping of SMN2 exon 7, and we show that WDM patients have increased levels of spliced SMN2 in skeletal muscle cells when compared with controls. Immunostaining of WDM muscle biopsies showed accumulation of TIA1 and stress granulae proteins adjacent to intracellular inclusions, a typical finding in WDM. The combined findings strongly suggest that the TIA1 mutation causes perturbed RNA splicing and cellular stress resulting in WDM. The selection against the mutation is likely to be negligible and the age of the TIA1 founder mutation was calculated to approximately 1,050 years, which coincides with the epoch of early seafaring across the Baltic Sea.

Autosomal dominant progressive external ophthalmoplegia Distribution of multiple mitochondrial DNA deletions

Objective: To relate signs and symptoms to morphologic changes and presence of multiple mitochondrial DNA (mtDNA) deletions in a patient with autosomal dominant progressive external ophthalmoplegia (adPEO) and mitochondrial myopathy. Background: An etiologic association between the somatic multiple mtDNA deletions in adPEO and clinical manifestations other than the myopathy has so far not been demonstrated. Methods: The authors investigated a patient with adPEO and multiorgan system manifestations including levodopa-responsive parkinsonism. She died at age 61 years of pancreatic carcinoma. Autopsy tissue specimens were investigated for morphologic alterations and occurrence of mtDNA deletions by Southern blot and long-extension PCR analyses. Results: The patient had carcinoma of the pancreas with metastases to liver, lymph nodes, and bone marrow. The brain revealed slight gliosis of the gray and white matter and degeneration of the substantia nigra. The myocardium showed focal areas with loss and atrophy of myocytes and fibrosis. Analysis of mtDNA revealed multiple deletions in different regions of the brain, skeletal muscle, and myocardium. Twenty-five different mtDNA deletions were identified. Most of these were flanked by large direct-sequence repeats. Six identical deletions were found in muscle and brain. Conclusions: These findings indicate that somatic multiple mtDNA deletions are associated with degenerative tissue changes and clinical manifestations in adPEO.

Analysis of the trinucleotide CAG repeat from the human mitochondrial DNA polymerase gene in healthy and diseased individuals.

The human nuclear gene (POLG) for the catalytic subunit of mitochondrial DNA polymerase (DNA polymerase γ) contains a trinucleotide CAG microsatellite repeat within the coding sequence. We have investigated the frequency of different repeat-length alleles in populations of diseased and healthy individuals. The predominant allele of 10 CAG repeats was found at a very similar frequency (approximately 88%) in both Finnish and ethnically mixed population samples, with homozygosity close to the equilibrium prediction. Other alleles of between 5 and 13 repeat units were detected, but no larger, expanded alleles were found. A series of 51 British myotonic dystrophy patients showed no significant variation from controls, indicating an absence of generalised CAG repeat instability. Patients with a variety of molecular lesions in mtDNA, including sporadic, clonal deletions, maternally inherited point mutations, autosomally transmitted mtDNA depletion and autosomal dominant multiple deletions showed no differences in POLG trinucleotide repeat-length distribution from controls. These findings rule out POLG repeat expansion as a common pathogenic mechanism in disorders characterised by mitochondrial genome instability.

Genomic duplications mediate overexpression of lamin B1 in adult-onset autosomal dominant leukodystrophy (ADLD) with autonomic symptoms

Adult-onset autosomal dominant leukodystrophy (ADLD) with autonomic symptoms features micturition urgency, constipation, erectile dysfunction, and orthostatic hypotension, usually followed by pyramidal signs and ataxia. Peripheral nerve conduction is normal. The disease is often mistaken for multiple sclerosis in the initial phase. There is a characteristic pattern of white matter changes in the brain and spinal cord on magnetic resonance imaging (MRI), mild atrophy of the brain, and a more marked atrophy of the spinal cord. ADLD is associated with duplications of the lamin B1 (LMNB1) gene but the mechanism by which the rearrangement conveys the phenotype is not fully defined. We analyzed four unrelated families segregating ADLD with autonomic symptoms for duplications of the LMNB1 gene. A single nucleotide polymorphism (SNP) array analysis revealed novel duplications spanning the entire LMNB1 gene in probands from each of the four families. We then analyzed the expression of lamin B1 in peripheral leukocytes by Western blot analysis in five patients from two available families. The protein levels of lamin B1 were found significantly increased. These results indicate that the ADLD phenotype associated with LMNB1 duplications is mediated by increased levels of the lamin B1 protein. Furthermore, we show that a molecular diagnosis for ADLD with autonomic symptoms can be obtained by a direct analysis of lamin B1 in peripheral leukocytes.