Neuropathology of Cytochrome b Deficiency Boleslaw Lach, Mark Tarnopolsky, Janet Simons, Samantha Marin, Lauren MacNeil and Steve Sommer McMaster University

CYTOCHROME B DEFICIENCY Five complexes > 80 proteins mDNA – encodes 13 polypeptides Mostly sporadic, very uncommon, probably less than 7% of mitochondrial disorders Rarely transmitted to offspring Some restricted to muscle Functionally associated with complex III Mutations: Stop codon , deletions, frame shift, termination and missense Encoded by mDNA One out of 11 polypeptides of complex III Located in the inner membrane

Cytochrome B deficiency with cardiac and neurological manifestations Figure 1. Mutation Amino Acid Reduced Complex III Activity Histopathology (muscle) Exercise Intolerance Fixed Weakness Elevated Resting Lactate Clinical Manifestations Reference m.14787_14790del frameshift Yes Mild RRF, variable COX staining + - Juvenile parkinsonism, MELAS, WPW, LV hypertrophy, epilepsy De Coo(13) m.14792C > G H16D NR, complex I def. Normal Dystonia, seizures, external ophthalmoplegia, episodic central apnea Ronchi (18) m.14849T>C S35P Fasting rhabdomyolysis, cognitive and motor delay, ataxia, LV hypertrophy, CRI, Septo-optic dysplasia Schuelke (11) m.15242G>A G166X Many RRFs, all COX+ MELAS, menorrhagia Keightley (9) m.15243G>A G166E Heart – Macrovesicular lipid storage Hypertrophic cardiomyopathy, cardiac failure Valnot (7) m.15498G>A G251D Heart – Increased lipid deposits Histiocystoid cardiomyopathy, hepatic steatosis, ATN Andreu (8) m.15579A>G Y278C RRF (17%), all COX+ Bilateral deafness, cognitive dysfunction, GH deficiency, cataracts, retinitis pigmentosa, epilepsy Wibrand (12) m.15699G>C R318P Yes, and complex I def. Mild RRF1%), normal COX staining Bilateral deafness, MELAS, fertility problems Blakely (10)

CLINICAL HISTORY – CASE #1 Born at normal gestational age with subtle dysmorphic features (epicanthal fold and high arch palate) Global developmental delay of unknown origin with attention deficit hyperactivity disorder (ADHD) Corrective surgery for strabismus at the age of 3 At 6 years of age – episode of acute creatinine kinase elevation and myoglobinuria after episode of gastrointestinal innocent fasting; frequent myalgias, nausea and occasional vomiting accompanying exercise or minute trauma; no visual or hearing loss Progressive muscle weakness and scoliosis requiring treatment with bracing at the age of 15 MR spectroscopy revealed elevated lactate peak in the basal ganglia and thalami; EKG – Wolfe-Parkinson-White syndrome; echocardiogram – mild left ventricular progressive dysfunction with decreased ejection fraction Elevated serum lactate 6-8 mmol/L (normal = 2.2 mmol/L), normal CSF lactate Biopsies at the age of 6 and 14 Family history: mother with mild proximal muscle weakness and normal muscle biopsy He died in his sleep at the age of 21.

6yo. biopsy NADH

14 yo.

Post-mortem: quadriceps Ragged red fibers NADH COX ORO

Diaphragm ORO Myocardium

Parietal White Matter S?tau? Calretinin Tau Neurofilaments

Occipital White Matter Subependymal era Synaptophysin Tau Calretinin Synaptophysin

Neurofilament OCCIPITAL CORTEX NF GFAP

Basilar Artery

Case #1 Mild cortical dysplasia White matter heterotopia- multifocal Cardiomyopathy Mitochondrial myopathy

CLINICAL HISTORY – CASE #2 Prematurely born at 27 weeks and 5 days gestational age (placental abruption) a) required brief respiratory support b) dysmorphic features (microcephaly, epicanthal fold, high arched palate, limited visual acuity to bright light, rapidly progressing to complete blindness) At 7 months – beginning of seizures, hypotonia At 3 years – rigidity, spasticity, decortication, lower extremity clonus, kyphoscoliosis and progressive respiratory failure Died at the age of 5 years and 4 months Family history: mother with history of migraines, strabismus, myalgias and depression; brother and two maternal uncles with myalgias and intermittent exercise intolerance; maternal grandmother ???? Laboratory findings: normal lactate in CSF and blood; CT – cerebral atrophy; MRI – delayed myelination and increased lactate; EEG – high voltage waves in the left temporal region; EKG – normal Muscle biopsies: 5 months – not remarkable; at 5 years – end stage muscle biopsies. mother, maternal grandmother and maternal great aunt – normal; brother – mitochondrial microangiopathy

HE HETERTOPIA Temporal lobe – meningeal heterotopia Occipital lobe– neuronal loss& WM atrophy HE HETERTOPIA NF GFAP

TEMPORAL LOBE NF

MBP CALR SYN SYN CALR NF

SMA CD34 SMA SMA

GFAP NF Olivary nucleus

Case #2 Cerebral cortical dysplasia Grey matter heterotopia in white matter Grey matter heterotopia in meninges Severe vasculopathy Cerebellar degeneration Brain atrophy Severe myopathy (end stage)

Novel sequence (m 15161T>C) Patient 1 Patient 2 Novel sequence (m 15161T>C) Substitution of serine with proline at amino acid position 139 Heteroplasmy in muscle 20%, not detected in blood 50% reduction in complex I and III in muscle biopsy No mutation in mother – de novo mutation Novel sequence (m 15152 G>A) Substitution of glycine with serine at amino acid position 139 Heteroplasmy in lymphocytes 58% Heteroplasmy in many brain areas: 50-68% Same variant in mother’s muscle sample with 18% heteroplasmy – maternal inheritance Same enzyme deficiency due to different pattern of inheritance. Severity of pathological changes and clinical manifestations related to degree and presence of heteroplasmy Shared developmental brain abnormalities, especially neuronal migration.

DEVELOPMENTAL CNS ABNORMALITIES IN MITOCHONDRIAL DISORDERS Agenesis of corpus callosum (Shevell et al, 1994) Massive leptomeningeal heterotopia (complex I + IV) Agenesis of corpus callosum with Leigh’s syndrome and microencephaly (Samson et al, 1994) Cerebellar hypoplasia (Lincke et al, 1996) Partial agenesis of corpus callosum (PDH) and microencephaly (Lissen et al, 1999) and complex I + IV von Kleist-Retzow (2003) Agenesis of corpus callosum, olivary dysplasia, absence of pyramidal system Infantile cerebral lactic acidosis (Chow et al, 1987, Brown et al, 1998) Dandy-Walker malformation (complex II, von Kleist-Retzow, 2003)

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