1. Genetic heterogeneity of mitochondrial disorders is high, with mutations in over 250 nuclear genes and 13 mitochondrial genes known to cause primary mitochondrial disorders. 2. Complex I deficiency is a common presentation and has high genetic and clinical heterogeneity, with mutations in over 30 nuclear genes associated. 3. Mitochondrial translation deficiency is another common presentation, with mutations in over 30 genes encoding mitochondrial aminoacyl-tRNA synthetases and other translation factors associated.
7. Leigh Syndrome
LHON
Neurogenic Muscle Weakness Ataxia and
Retinitis Pigmentosa
Encephalomyopathy, MELAS
Epilepsy
MM, Exercise Intolerance
Cardiomyopathy
Deafness
Diabetes Mellitus
Alzheimer & Parkinson Disease
Idiopathic Sideroblastic Anemia
mtDNA point mutations
Reported in Mitomap:
rRNA/tRNA mutations: 306 mutations
Coding and Control Region Point Mutations: 311
mtDNA deletions: 134
MITOMAP
A human mitochondrial genome database
http://www.mitomap.org/MITOMAP
8. mtDNA variations
Polymorphisms
usually homoplasmic
transmitted
homoplasmy homoplasmyheteroplasmy
Mutations
usually heteroplasmic
transmitted or de novo
high mutant load in patient
low mutant load in mother
0% mutation in mother
high mutant load in affected organs
low mutant load in non affected organs
mtDNA mutations: 10% of pediatric patients
23 haplogroups associating
specific polymorphisms
9. Leigh syndrome
Hyperlactatemia
Improvement at 3 yrs
Leigh syndrome
Hyperlactatemia
Multiple RC deficiency
Death at 6 mo
mt-tRNAGlu
100% 14674T>C
100%
14674T>C
100%
14674T>C
100%
14674T>C
100%
14674T>C
100%
14674T>C
Onset: first days or weeks of life
Hypotonia
Respiratory and feeding difficulties
Hyperlactatemia
One patient died of severe hypotonia at 39 days
All other improved spontaneously (4-20 months)
100% 14674T>C mt-tRNAGlu
in all patients
in all maternal relatives
mtDNA mutation or polymorphism?
Horvath et al, Brain 2009
10. Leber hereditary optic neuropathy
Onset 15-30 yrs
Most common of the primary mtDNA diseases
Prevalence: 1/40 000 in Europe
2% of visually impaired people suffer LHON
Incomplete penetrance
50% of males and 10% of females with LHON mutation develop the optic neuropathy
genetic and/or environmental factors
ND4 (G11778A)
ND6 (T14484C)
cytb (G15257A)
maternal transmission
homoplasmic/heteroplasmic
11. mtDNA polymorphisms
11778G>A and 14484T>C mutations higher risk of visual failure with haplogroup J
3460G>A mutation higher risk of visual failure with haplogroup K
11778G>A mutation lower risk of visual loss with haplogroup H
Leber hereditary optic neuropathy
Environmental factors
discordant monozygotic twins
? increased risk of visual loss with high tobacco and alcohol consumption
? nutritional deprivation, exposure to industrial toxins, antiretroviral drugs, psychological
stress or acute illness
Nuclear genetic factors
predominance of affected males in LHON recessive X-linked susceptibility gene?
no skewed X chromosome inactivation in affected female carriers
two loci Xp21–Xq21 and Xq25–27 but no identified gene
Genetic factors
12. Mitochondrial DNA mutations
Genes encoding subunits of the respiratory chain
CI
CII
CIII CIV CV
ND1
ND2
ND3
ND4
ND5
ND6 cytb
ATP6
ATP8
COXI
COXII
COXIII
Necker hospital: 33 patients 1 patient 1 patient 20 patients
mtDNA mutations: 10% of pediatric patients
13. Mitochondrial disorders
Relative clinical homogeneity but high genetic heterogeneity:
Complex I deficiency
High clinical and genetic heterogeneity:
Translation deficiency
multiple 51%
(555 patients)
CI 22% (250 patients)
CII 4%
CIII 2,5%
CIV 13%
CV 7%
Q 1%
17. Bilateral brainstem lesions (30/30)
Lactate peak (30/30)
Anomalies of the putamen (23/30)
Brain MRI in complex I deficient patients
Brain MRI (Axial T2)
brainstem lenticular nuclei and thalami
Magnetic resonance
spectroscopy
30 patients with isolated complex I deficiency
20 mtDNA mutations
10 nuclear gene mutations
Lebre, JMG 2010
18. Patients with nuclear gene mutations
Earlier brain MRI anomalies than patients with mtDNA mutations
(2.8 years and 8.9, respectively, p<0.05)
Mutations in complex I genes cause a common pattern of brain MRI imaging
Brainstem and basal ganglia anomalies
+ Lactate peak
but no corpus callosum dysmorphism
Stroke-like lesions
40% of patients with mtDNA mutations
none of the patients with nuclear gene mutations
Supratentorial leucoencephalopathy
50% of patients with nuclear gene mutations
none of the patients carrying mtDNA mutations
Brain MRI in complex I deficient patients
Lebre, JMG 2010
19. Mitochondrial disorders
Relative clinical homogeneity but high genetic heterogeneity:
Complex I deficiency
High clinical and genetic heterogeneity:
Translation deficiency
multiple 51%
(555 patients)
CI 22% (246 patients)
CII 4%
CIII 2,5%
CIV 13%
CV 7%
Q 1%
translation deficiency: 69 patients
23. Gene Protein
RNF207 ring finger protein 207
SEC16B SEC16 homolog B (S. cerevisiae)
CCNT2 cyclin T2
MTRF1L mitochondrial translational release factor 1-like
SERAC1 serine active site containing 1
MXRA5 matrix-remodelling associated 5
Which gene?
IUGR
D1 lactic acidosis
D4 liver insufficiency
Hypotonia
Brain MRI: thalamus, lactate peak
Death at 7 mo
Multiple RC deficiency in liver
24. Gene Protein
RNF207 ring finger protein 207
SEC16B SEC16 homolog B (S. cerevisiae)
CCNT2 cyclin T2
MTRF1L mitochondrial translational release factor 1-like
SERAC1 phospholipid remodeling
MXRA5 matrix-remodelling associated 5
homozygous c.107T>A, p.Leu36Gln
SIFT: Deleterious
MutationTaster: Disease causing
Polyphen: Probably damaging
MTRF1L A/T MTRF1L A/T
MTRF1L A/A MTRF1L A/A
Which gene?
IUGR
D1 lactic acidosis
D4 liver insufficiency
Hypotonia
Brain MRI: thalamus, lactate peak
Death at 7 mo
Multiple RC deficiency in liver
25. Gene Protein
RNF207 ring finger protein 207
SEC16B SEC16 homolog B (S. cerevisiae)
CCNT2 cyclin T2
MTRF1L mitochondrial translational release factor 1-like
SERAC1 phospholipid remodeling (interface mito/ER)
MXRA5 matrix-remodelling associated 5
homozygous c.107T>A, p.Leu36Gln
SIFT: Deleterious
MutationTaster: Disease causing
Polyphen: Probably damaging
c.1122_1124dup, p.Tyr375*
IUGR
D1 lactic acidosis
D4 liver insufficiency
Hypotonia
Brain MRI: thalamus, lactate peak
Death at 7 mo
Multiple RC deficiency in liver
MTRF1L A/T MTRF1L A/T
MTRF1L A/A MTRF1L A/A
SERAC1 dup/dupSERAC1 dup/dup
SERAC1 dup/wt SERAC1 dup/wt
Which gene?
26. SERAC1MTRF1L
Mitochondrial translational release
factor 1-like
No reported mutation
Liver: RC defect (I IV)
Phospholipid remodeling (interface mito/ER)
MEGDEL syndrome
deafness, encephalopathy, and Leigh-like syndrome
3-methylglutaconic aciduria
Wortmann Nat Genet 2012
Mitochondrial hepatopathy
Sariq et al Am J Med Genet 2013
our patient:
Hepatopathy
Leigh syndrome
Slight 3-methylglutaconic aciduria
mtDNA depletion
isolated
syndromic
mtDNA translation
TRMU
GFM1
TSFM
DGUOK
POLG
PEO1
MPV17
unknown
gene
unknown
gene
MTRF1L or SERAC1 ?
MTRF1L chr6:152,987,362-153,002,685
SERAC1 chr6:158,109,515-158,168,270homozygosity region: 150,535,865-165,801,958
27. 28 patients:
non mitochondrial disease
112 patients with suspected mitochondrial disease
and whole exome or targeted exome sequencing
8/29 hyperlactatemia
(27%)
84 patients:
gene encoding mitochondrial protein
52/83 hyperlactatemia
(63%)
Criteria for mitochondrial disease:
Clinical presentation
Course of the disease
Brain MRI
Metabolic data
RC analysis/assembly
Exome sequencing allows us to better define criteria
for mitochondrial disorders diagnosis
ABCB11
AP4M1
CDG1J
COG5
ECHS1
EXOCS3
GFAP
MUNC18
PCCB
PPP2R5D
PRPS1
SCA37
SEPSECS
SLC6A8
SRRM2
WDR81
28. Exome sequencing allows us to better define criteria
for mitochondrial disorders diagnosis
28 patients:
non mitochondrial disease
84 patients:
gene encoding mitochondrial protein
Criteria for mitochondrial disease:
Clinical presentation
Course of the disease
Brain MRI
Metabolic data
RC analysis/assembly
mitochondrial non mitochondrial
criteria for mitochondrial disease
0
5
10
15
20
25
0 1 2 3 4 5 6 7 0 0 1 2 3
nbofpatients
nb patients
112 patients with suspected mitochondrial disease
and whole exome or targeted exome sequencing
30. Mitochondrial disorders
clinical heterogeneity
genetic heterogeneity
one genotype
one phenotype
Hepatic failure
one genotype
various phenotypes
dominant
adPEO
recessive
Alpers syndrome
Hepatic failure
various genotypes
one phenotype
Hepatic failure
DGUOK POLG DGUOK
POLG
TRMU
31. genomit - ERA-Net E-Rare
Imagine Institut
Metodi METODIEV
Benedetta RUZZENENTE
Anthony DRECOURT
Juliette PULMAN
Christelle TAMBY
Lucas BIANCHI
Coralie ZANGARELLI
Christine BOLE
Patrick NITSCHKE
Department of Genetics
and of Pediatrics
Zahra ASSOULINE
Giulia BARCIA
Julie STEFFANN
Jean-Paul BONNEFONT
Marlène RIO
Nathalie BODDAERT
Isabelle DESGUERRE
Pascale de LONLAY
Arnold MUNNICH