Transcript Development of a UK diagnostic service for Meckel

Development of a UK diagnostic
service for Meckel-Gruber syndrome
Helen Lindsay, Kimberley Flintoff, David Cockburn,
Ruth Charlton and Colin Johnson
Yorkshire Regional DNA Laboratory
Overview
• Meckel-Gruber syndrome (MKS)
– Clinical features
– Genetic aspects
• MKS mutation spectrum
• Screening test strategy
• Achievements to date
Meckel-Gruber syndrome (MKS)
Clinical features
• Lethal developmental disorder
• UK incidence approximately 1 in 30,000
• ‘Classic triad’ of features (Salonen, 1984):
– occipital encephalocele (or other CNS
abnormality)
– bilateral large multicystic kidneys
– fibrotic changes in the liver
• other features: bilateral postaxial polydactyly,
microphthalmia, cleft lip and palate, heart defects,
genetic abnormalities, bowing of long bones, situs
inversus, low set ears etc.
Diagnosis
• Via ultrasound at 11-14 weeks
• Often an autopsy is necessary
Genetic aspects
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•
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Associated with the dysfunction of primary cilia
Autosomal recessive
Genetic and clinical heterogeneity
Oligogenic inheritance
Map
Function
Reference
MKS1
17q22
Kyttälä et al. (2006)
MKS2
11q13
novel: cytoplasmic protein,
contains B9 domain, localises
to basal bodies
-
MKS3/TMEM67
8q22.1
Smith et al. (2006)
MKS4/CEP290/
NPHP6
12q21
novel: Frizzled-like receptor,
localises to primary cilia &
basal bodies
centrosomal protein; causative
of other ‘ciliopathies’
MKS5/RPGRIP1L
16q12.2
Roume et al. (1998)
Baala et al. (2007)
novel: colocalises and interacts Delous et al. (2007)
with other ciliary proteins
Genetic aspects
•
•
•
•
Associated with the dysfunction of primary cilia
Autosomal recessive
Genetic and clinical heterogeneity
Oligogenic inheritance
Map
Function
Reference
MKS1
17q22
Kyttälä et al. (2006)
MKS2
11q13
novel: cytoplasmic protein,
contains B9 domain, localises
to basal bodies
-
MKS3/TMEM67
8q22.1
Smith et al. (2006)
MKS4/CEP290/
NPHP6
12q21
novel: Frizzled-like receptor,
localises to primary cilia &
basal bodies
centrosomal protein; causative
of other ‘ciliopathies’
MKS5/RPGRIP1L
16q12.2
Roume et al. (1998)
Baala et al. (2007)
novel: colocalises and interacts Delous et al. (2007)
with other ciliary proteins
MKS1 and MKS3 mutations
MKS3/Meckelin
MKS1
B9 domain
Khaddour et al. (2007) Human Mutation 28(5); 523-4
The need for a diagnostic service for MKS
• Prior to this project, no CPA accredited laboratory offered MKS
testing
• Mutation scanning performed on a research basis by Dr Colin
Johnson at the Leeds Institute of Molecular Medicine
– approximately 50 requests, nationally and internationally, for
screening annually
• In the local population the incidence of MKS may be as high as
1 in 3000
• A diagnostic service would allow
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–
–
–
accurate diagnosis
confirmation of research results
carrier testing in at-risk individuals
prenatal testing
Proposed test strategy
Referrals to DNA Lab
Pakistani origin
Other origin
Screen for common MKS3 splice-site mutations
Autozygosity or linkage analysis at MKS1 & MKS3
Targeted mutation screen by sequencing
• Clinical sensitivity of testing for mutations in MKS1 and MKS3 in
the general population is approximately 15%
• In the local Pakistani population sensitivity for the MKS3
c.1575+1G>A mutation alone is estimated at 40%
The story so far...
• Bidirectional sequencing optimised for:
– entire coding region of MKS1 (18 exons)
– exons 1-18 of MKS3
• Microsatellite analysis for MKS1 and MKS3 loci optimised:
– MKS1 17q22
– MKS3 8q22
D17S1853 and D17S1290
D8S1818 and D8S1699
• Reports issued:
– 35 confirmations of research findings
• 30 locally
• 5 nationally
– it is anticipated that these results will lead to cascade carrier testing
and prenatal diagnosis requests
• Gene dossier to be submitted to UKGTN April 2008
Mutations reported
482 483 484
485
486
487
488
Thr Thr Gly Thr Val Thr Phe
MKS1
•
c.1451_1453dupGGCA (p.Thr485fs)
– Pakistani
– 4bp duplication in exon 16
Thr Thr Gly Arg His Cys His
MKS3
• c.1674+1G>A
– Pakistani
– mutation abolishes exon 16 splice donor site
Upper panel: wild-type
Lower panel: homozygous mutant
Exon16 |
Intron 16
Mutations reported
Exon 15
|
Intron 15
MKS3
• c.1575+1G>A
– Pakistani
– mutation abolishes exon 15 splice donor site
– Estimated allele frequency in the local Pakistani population is
0.016; carrier frequency approximately 1/32
– Variable phenotype e.g. CNS, polydactyly. Inter- and intra-familial
variation
• c.870-2A>G
– Pakistani
– mutation abolishes exon 9 splice acceptor site
Upper panel: wild-type
Lower panel: homozygous mutant
Intron 8
| Exon 9
MKS testing costs
Two common Pakistani mutations
£200
Microsatellite analysis
£100 per person
Sequencing (per gene)
up to £1000
Known mutation
£150
Please contact the laboratory for further information on testing for
Meckel-Gruber syndrome.
[email protected]
Acknowledgements
Leeds Institute of Molecular Medicine
• Colin Johnson
Yorkshire Regional DNA Laboratory
• Kim Flintoff, David Cockburn, Ruth Charlton
Yorkshire Clinical Genetics Service
• Chris Bennett