R. Van Coster

Clinical spectrum of early-onset epileptic: encephalopathies associated with STXBP1 mutations

Objectives: Heterozygous mutations in STXBP1, encoding the syntaxin binding protein 1, have recently been identified in Ohtahara syndrome, an epileptic encephalopathy with very early onset. In order to explore the phenotypic spectrum associated with STXBP1 mutations, we analyzed a cohort of patients with unexplained early-onset epileptic encephalopathies. Methods: We collected and clinically characterized 106 patients with early-onset epileptic encephalopathies. Mutation analysis of the STXBP1 gene was done using sequence analysis of the exon and intron–exon boundaries and multiplex amplification quantification to detect copy number variations. Results: We identified 4 truncating mutations and 2 microdeletions partially affecting STXBP1 in 6 of the 106 patients. All mutations are predicted to abolish STXBP1 function and 5 mutations were proven to occur de novo. None of the mutation-carrying patients had Ohtahara syndrome. One patient was diagnosed with West syndrome at disease onset, while the initial phenotype of 5 further patients did not fit into a specific recognized epilepsy syndrome. Three of these patients later evolved to West syndrome. All patients had severe to profound mental retardation, and ataxia or dyskinetic movements were present in 5 patients. Conclusion: This study shows that mutations in STXBP1 are not limited to patients with Ohtahara syndrome, but are also present in 10% (5/49) of patients with an early-onset epileptic encephalopathy that does not fit into either Ohtahara or West syndrome and rarely in typical West syndrome. STXBP1 mutational analysis should be considered in the diagnostic evaluation of this challenging group of patients.

Pyruvate Carboxylase Deficiency: A Benign Variant with Normal Development

ABSTRACT: The devastating nature of a pyruvate carboxylase deficiency is underscored by the uniformly fatal outcome of the neonatal (French) type and the severely disabling and ultimately fatal outcome of the infantile (North American) type. We report a γ-y-old girl with metabolic and biochemical features of the North American phenotype. Remarkably, the clinical course has been benign with preservations of motor and mental abilities. The residual enzyme activity in cultured skin fibroblast homogenates was 1.8% and cross-reacting material was present in normal abundance and electrophoretic mobility. She has had several episodes of metabolic acidosis with elevated lactate, pyruvate, alanine, β-hydroxybutyrate, acetoacetate, lysine, and proline values, and undetectably low aspartate concentrations. These crises have been managed by rehydration and bicarbonate therapy. We are unable to provide a satisfactory explanation for the uniquely benign clinical course that has been experienced by this patient.

Cardiofaciocutaneous (CFC) syndrome associated with muscular coenzyme Q10 deficiency.

SummaryThe cardiofaciocutaneous (CFC) syndrome is characterized by congenital heart defect, developmental delay, peculiar facial appearance with bitemporal constriction, prominent forehead, downslanting palpebral fissures, curly sparse hair and abnormalities of the skin. CFC syndrome phenotypically overlaps with Noonan and Costello syndromes. Mutations of several genes (PTPN11, HRAS, KRAS, BRAF, MEK1 and MEK2), involved in the mitogen-activated protein kinase (MAPK) pathway, have been identified in CFC–Costello–Noonan patients. Coenzyme Q10 (CoQ10), a lipophilic molecule present in all cell membranes, functions as an electron carrier in the mitochondrial respiratory chain, where it transports electrons from complexes I and II to complex III. CoQ10 deficiency is a rare treatable mitochondrial disorder with various neurological (cerebellar ataxia, myopathy, epilepsy, mental retardation) and extraneurological (cardiomyopathy, nephropathy) signs that are responsive to CoQ10 supplementation. We report the case of a 4-year-old girl who presented a CFC syndrome, confirmed by the presence of a pathogenic R257Q BRAF gene mutation, together with a muscular CoQ10 deficiency. Her psychomotor development was severely impaired, hindered by muscular hypotonia and ataxia, both improving remarkably after CoQ10 treatment. This case suggests that there is a functional connection between the MAPK pathway and the mitochondria. This could be through the phosphorylation of a nuclear receptor essential for CoQ10 biosynthesis. Another hypothesis is that K-Ras, one of the proteins composing the MAPK pathway, might be recruited into the mitochondria to promote apoptosis. This case highlights that CoQ10 might contribute to the pathogenesis of CFC syndrome.

Fungal intracranial aneurysm in a child with familial chronic mucocutaneous candidiasis

Abstract We report on a patient who presented at 5 years of age with a hemiparesis due to a middle cerebral artery infarction. An embolism had originated from a mycotic aneurysm located in the internal carotid artery. For several months prior to admission he had been suffering from therapeutically resistant candidiasis of the mouth and nails. Family history revealed chronic mycotic infections of the skin, hair, nails and mouth in the father and paternal grandmother suggestive of chronic mucocutaneous candidiasis with autosomal dominant mode of inheritance. Clipping of the aneurysm, after 3 months of anti-mycotic treatment, followed by sustained treatment with itraconazole and fluconazole, led to a favourable outcome. Conclusion Chronic mucocutaneous candidiasis can be associated with an intracranial aneurysm and complicated by cerebral infarction.

Progressive myoclonic epilepsy as an adult-onset manifestation of Leigh syndrome due to m.14487T > C

Background: m.14487T>C, a missense mutation (p.M63V) affecting the ND6 subunit of complex I of the mitochondrial respiratory chain, has been reported in isolated childhood cases with Leigh syndrome (LS) and progressive dystonia. Adult-onset phenotypes have not been reported. Objectives: To determine the clinical–neurological spectrum and associated mutation loads in an extended m.14487T>C family. Methods: A genotype–phenotype correlation study of a Belgian five-generation family with 12 affected family members segregating m.14487T>C was carried out. Clinical and mutation load data were available for nine family members. Biochemical analysis of the respiratory chain was performed in three muscle biopsies. Results: Heteroplasmic m.14487T>C levels (36–52% in leucocytes, 97–99% in muscle) were found in patients with progressive myoclonic epilepsy (PME) and dystonia or progressive hypokinetic-rigid syndrome. Patients with infantile LS were homoplasmic (99–100% in leucocytes, 100% in muscle). We found lower mutation loads (between 8 and 35% in blood) in adult patients with clinical features including migraine with aura, Leber hereditary optic neuropathy, sensorineural hearing loss and diabetes mellitus type 2. Despite homoplasmic mutation loads, complex I catalytic activity was only moderately decreased in muscle tissue. Interpretation: m.14487T>C resulted in a broad spectrum of phenotypes in our family. Depending on the mutation load, it caused severe encephalopathies ranging from infantile LS to adult-onset PME with dystonia. This is the first report of PME as an important neurological manifestation of an isolated mitochondrial complex I defect.

Adult Reye's syndrome A review with new evidence for a generalized defect in intramitochondrial enzyme processing

A 42-year-old woman developed a flu-like illness and died 8 days later with Reyes syndrome (RS). There are 26 other cases of adult-onset RS reported. Biochemical, immunologic, and molecular studies of liver, brain, and skeletal muscle revealed a non-uniform decrease in several mitochondrial residual enzyme activities in liver and brain. Pyruvate carboxylase activity was negligible. Cross-reacting material was present in normal abundance in isolated liver mitochondria for several enzymes that had reduced catalytic activity including pyruvate carboxylase. Subunit II (encoded by mitochondrial DNA) and subunit IV (encoded by nuclear DNA) of cytochrome c oxidase also were present in normal abundance with normal electrophoretic mobility. These observations, combined with pertinent findings of other investigators, allow us to speculate that the intramitochondrial matrix chemical environment is disturbed by preceding pathophysiologic events resulting in a lowered ATP/ADP ratio. The lowered intramitochondrial energetic state interferes with the refolding and assembly of imported mitochondrial proteins, causing a loss of the catalytic efficiency of these enzymes. This explains the selective vulnerability of mitochondria in RS and the non-uniform, disproportionate loss of enzyme activity.

Repetitions in final position in a nine-year-old boy with focal brain damage

This paper describes the final repetitions displayed by a nine-year-old boy with a history of cerebral trauma. The dysfluencies that he evidenced are somewhat different from those reported in previous studies in that his final repetitions tended to involve an entire syllable or the nucleus and coda of a syllable rather than an individual sound. Also, they co-occurred with whole-word repetitions of terminal words of utterances. This raises the possibility that this symptomatology represents a form of palilalia.

Immunohistochemical analysis of the oxidative phosphorylation complexes in skeletal muscle from patients with mitochondrial DNA encoded tRNA gene defects.

Background: Mitochondrial diseases display a heterogeneous spectrum of clinical phenotypes and therefore the identification of the underlying gene defect is often a difficult task. Aims: To develop an immunohistochemical approach to stain skeletal muscle for the five multi-protein complexes that organise the oxidative phosphorylation (OXPHOS) in order to improve the diagnostic workup of mitochondrial defects. Methods: OXPHOS complexes were visualised in skeletal muscle tissue using antibodies directed against different subunits. The staining patterns of patients with heteroplasmic defects in mtDNA tRNA genes were compared with those of normal and disease controls. Results: Normal skeletal muscle displayed a checkerboard staining pattern for complexes I to V due to the higher mitochondrial content of slow muscle fibres versus fast fibres. In patients with tRNA defects, a much more heterogeneous staining pattern was observed for complex I (all six patients) and complex IV (4 of 6 patients): a mosaic staining pattern in which individual fibres displayed staining intensities that ranged from strong to negative. Ragged red fibres (RRFs) in patients with MERRF (myoclonic epilepsy and ragged red fibres) were all complex I and IV negative, while in patient with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes) the majority of RRFs were complex I negative and complex IV positive. Conclusion: Immunohistochemical detection of OXPHOS complexes could represent a valuable additional diagnostic tool for the evaluation of mitochondrial cytopathy. The technique helps to detect heteroplasmic mtDNA defects. Staining for complex I in particular was able to identify two tRNA patients that stayed undetected with routine histochemical evaluation.

Ultrastructural mitochondrial alterations in Equine myopathies of unknown origin.

Background: Very few mitochondrial myopathies have been described in horses. Objective: To examine the ultrastructure of muscle mitochondria in equine cases of myopathy of unknown origin. Materials & methods: Biopsies of vastus lateralis of the Musculus quadriceps femoris were taken predominantly immediately post mortem and processed for transmission electron microscopy. As a result, electron micrographs of 90 horses in total were available for analysis comprising 4 control horses, 16 horses suffering from myopathy and 70 otherwise diseased horses. Results: Following a thorough clinical and laboratory work-up, four out of five patients that did not fit into the usual algorithm to detect known causes of myopathy showed ultrastructural mitochondrial alterations. Small mitochondria with zones with complete disruption of cristae associated with lactic acidemia were detected in a 17-year-old pony mare, extremely long and slender mitochondria with longitudinal cristae in a 5-year-old Quarter horse stallion, a mixture of irregular extremely large mitochondria (measuring 2500 by 800 nm) next to smaller ones in an 8-year-old Hanoverian mare and round mitochondria with only few cristae in a 11-year-old pony gelding. It remains uncertain whether the subsarcolemmal mitochondrial accumulations observed in the fifth patient have any pathological significance. Conclusions: Ultrastructural alterations in mitochondria were detected in at least four horses. To conclude that these are due to mitochondrial dysfuntions, biochemical tests should be performed. Practical applications: The possibility of a mitochondrial myopathy should be included in the differential diagnosis of muscle weakness.

PP03.14 – 2978: Massive early leukoencephalopathy caused by a pathogenic mutation in IBA57: A new clinical presentation for this recently described gene defect

Objective Unraveling the underlying molecular defect in a patient with early onset progressive leukoencephalopathy and combined OXPHOS deficiency involving complex I and II. Methods After homozygosity mapping and whole exome sequencing a candidate gene was identified. Pathogenicity was assessed by means of functional studies in HeLa cells and western blotting in patient material. Results In a patient presenting with psychomotor retardation, massive white matter alterations and the presence of high lactate were detected on MRI, and a combined complex I and II deficiency was found in skeletal muscle. This combined complex deficiency is very suggestive of a defective iron-sulfur cluster (ISC) biosynthesis, a suspicion which was further strengthened by absence of lipoic residues in aKGDH and PDH. Homozygosity mapping revealed several candidate genes involved in ISC biogenesis: NFU1, BOLA3, IBA57 and ABCB10. Whole exome sequencing identified a homozygous variant in IBA57 [c.436C> T. (p.Arg146Trp)]. Complementation studies in HeLa cells depleted of wild type IBA57 and transfected with mutant IBA57 showed deficient lipoylation and lowered expression of a complex II subunit. Conclusion By combining a biochemical and molecular approach the underlying genetic cause for this patients phenotype could be unraveled. This is the third report of a pathogenic variant in IBA57 and discloses the clinical and neuroradiological heterogeneity of this gene defect. At the biochemical level a combined complex I and II deficiency and absence of lipoylation seems to be a uniform finding.