mitochondrial complex iii deficiency associated with a homozygous mutation in uqcrq ortal barel
DESCRIPTION
Mitochondrial complex III deficiency associated with a homozygous mutation in UQCRQ Ortal Barel Laboratory of Dr. Ohad Birk Ben Gurion University Beer-Sheva, Israel. The Israeli Bedouin. Isolated inbred population High rate of consanguineous marriage Negev region of southern Israel - PowerPoint PPT PresentationTRANSCRIPT
Mitochondrial complex III deficiency
associated with a homozygous mutation in
UQCRQ
Ortal BarelOrtal Barel
Laboratory of Dr. Ohad BirkLaboratory of Dr. Ohad Birk
Ben Gurion UniversityBen Gurion University
Beer-Sheva, IsraelBeer-Sheva, Israel
The Israeli Bedouin
Isolated inbred population
High rate of consanguineous marriage
Negev region of southern Israel
High frequency of autosomal recessive diseases
Effective in mapping genes of rare Recessive diseases
B
Pedigree of the Affected Israeli-Bedouin Kindred
Severe neurological syndrome.
Autosomal recessive pattern of inheritance
62 DNA samples
More than 25 affected individuals
Markedly uniform phenotype
Early onset in infancy
Severe psychomotor retardation
Extrapyramidal signs (age 2-3 years):
Dystonic postures, athetoid movements and ataxia
Severe defects in verbal receptive communication
Near total absence of expressive communication skills (verbal)
Hypotonia (inability to walk unsupported)
The hallmarks of the phenotype:
MRI studies
Bilateral symmetrical abnormal findings in the basal ganglia Increased density in the putamen and decreased density and size of the caudate and globus pallidum nuclei. No involvement of the brain-stem area.
MRI Studies of Affected Individual at Age 2 Years
Normal section
Muscle biopsy
Muscle biopsies were done in three of the affected individuals (ages 3, 15 and 2 years).
- Preserved architecture of the skeletal muscle
- Nonspecific histological findings
Metabolic work up:
- All laboratories values were within the normal range except:
Elevated serum lactate and pyruvate
Elevated Cerbrospinal fluid (CSF) lactate
Enzymatic activities of the mitochondrial respiratory chain
AssayP1P2P3
Complex I45%45%52%
Complex I+III43%70%74%
Complex II+III86%89%114%
Complex II79%94%92%
Complex III62%66%44%
Complex IV95%94%80%
Complex V135%94%82%
Enzymatic activities of the five mitochondrial respiratory-chain complexes were measured in isolated muscle mitochondria. 34%–56% decrease in the activity of mitochondrial complex III Variable decreases complex III + I
Mitochondrial disease
Summary of the phenotype and the clinical features:
Autosomal recessive
Elevated serum lactate and pyruvate
Decreased activity of mitochondrial complex III & I
Neurological abnormalities
Involvement of tissues characteristic of mitochondrial diseases (high energy consumption)
Complex III is located within the inner mitocondrial membrane Transfers electrons from ubiquinol to cytochrome c Complex III is made up of 11 subunits Genes associated with complex III deficiency:
Cytochrome b (mitochondrial DNA)
BCSIL - CIII assembly essential factor (2q33)
UQCRB - ubiquinone-binding protein (8q22)
Mitochondrial complex III, background:
Genome-wide linkage analysis results
D5S471
D5S2115
15.84 Mb
Founder effect
Ruled out: BCSIL and UQCRB
Genome-wide linkage analysis
(11 affected individuals; 5 healthy individuals)
A single locus; 9 cM; chromosome 5q31
5q31 Fine mapping
DNA samples of the 62 available family members (20 affected)
Family B: Many crossing over events in the maternal haplotype
A B
Region common to all affected individuals
Fine mapping of the homozygosity regions in the haplotype, demonstrate a region around D5S2002 which is common to all affected individuals in the family
Mapping two more family branches resulted in setting the lower (telomeric) limit of the homozygosity interval
at D5S2497
Compilation Table: Genotypes of All Affected Individuals
The shaded areas indicate the region of homozygosity markers. Upper limit of the homozygosity interval: D5S2057 Lower limit of the homozygosity interval: D5S2497
Results of Two-Point LOD Score Analysis
Analysis using SUPERLINK software
LOD score of 8.82 at θ= 0 for marker D5S_2
Locus defined between markers D5S2057 and D5S2497
2.14 cM interval of homozygosity common to all affected individuals
Contains 30 known or predicted genes
The disease locus
UQCRQ
Official Full Name:
Ubiquinol-cytochrome c reductase, complex III subunit VII, 9.5kDa (QCR8; QP-C )
Summary:
Encodes a ubiquinone-binding protein of low molecular mass.
The protein is a small core-associated protein and a subunit of mitochondrial complex III.
The bc1 complex (complex III ) contains 11 subunits:
- 3 respiratory subunits (cytochrome b, cytochrome c1 and Rieske)
- 2 core proteins (UQCRC1 and UQCRC2)
- 6 low-molecular weight proteins (UQCRH, UQCRB, UQCRQ, UQCR10, UQCR11 and a cleavage product of Rieske)
Affected Carrier unaffected
C208T Mutation in Exon 2 of UQCRQ
DNA: c.208 C to T mutation in exon 2 of UQCRQ
Protein: replacing serine at position 45 by phenylalanine (p.Ser45Phe)
Barel et al. The American Journal of Human Genetics (2008).
Mutation or SNP ???
NCBI database: rs11544803
Sequencing all other 29 genes at the locus revealed no other mutations
Predicted SNP only (without validation experiments).
Analysis of 62 DNA samples of the kindred: compatible with the mutation
Controls: 600 ethnically matched chromosomes
470 unrelated non-Bedouin chromosomes
242bp
190bp
147bp
111bp
203bp173bp
Healthy
HinfI
Affected
ClustalW Results:
Mutation: Serine to Phenylalanine
There is no phenylalanine in any of the homologues of UQCRQ gene
Phenylalanine has an aromatic side chain, leading to a significantly different three-dimensional structure.
Ser45: Phe45:
PDB: Bovine complex III with chain 7 (UQCRQ) in blue
Dr. Ohad Birk’s group
Dr. Rivka Ofir
Dr. Sara Sivan
The Lab members
Dr. Zamir Shorer Pediatric Neurology, Soroka Medical Center, Beer-Sheva, Israel
Dr. Ann Saada (Reisch) Metabolic Disease Unit, Hadassah Medical Center, Jerusalem
Dr. Stavit Shalev Genetics Institute, HaEmek Medical Center, Afula
Asi Cohen, Dr. Noam Zilberberg Lab, Department of Life Sciences, BGU
The Kahn Family Foundation
The Ori’s Foundation - In Memory of Ori LeviFoundation that supports research for the diagnosis, treatment and cure of mitochondrial disorder
(www.orifund.org)
Acknowledgements: