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

2. 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

3. 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)

4. 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.

5. 6yo. biopsy
NADH

6. 14 yo.

7. Post-mortem: quadriceps
Ragged red fibers
NADH
COX
ORO

8. Diaphragm
ORO
Myocardium

9. Parietal White Matter
S?tau?
Calretinin
Tau
Neurofilaments

10. Occipital White Matter
Subependymal era
Synaptophysin
Tau
Calretinin
Synaptophysin

11. Neurofilament
OCCIPITAL CORTEX NF
GFAP

12. Basilar Artery

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

14. 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

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

16. TEMPORAL LOBE NF

17. MBP
CALR
SYN
SYN
CALR NF

18. SMA
CD34
SMA
SMA

19. GFAP NF
Olivary nucleus

20. 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)

21. 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 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.

22. 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)

24. Thank you