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
• • • • Associated with the dysfunction of primary cilia Autosomal recessive Genetic and clinical heterogeneity Oligogenic inheritance
MKS1 MKS2
Map 17q22 11q13 Function novel: cytoplasmic protein, contains B9 domain, localises to basal bodies - Reference Kyttälä et al. (2006) Roume et al. (1998)
MKS3/TMEM67
8q22.1
MKS4/CEP290/ NPHP6
12q21 MKS5/RPGRIP1L 16q12.2 novel: Frizzled-like receptor, localises to primary cilia & basal bodies centrosomal protein; causative of other ‘ciliopathies’ Smith et al. (2006) Baala et al. (2007) novel: colocalises and interacts with other ciliary proteins Delous et al. (2007)
Genetic aspects
• • • • Associated with the dysfunction of primary cilia Autosomal recessive Genetic and clinical heterogeneity Oligogenic inheritance
MKS1 MKS2
Map 17q22 11q13 Function novel: cytoplasmic protein, contains B9 domain, localises to basal bodies - Reference Kyttälä et al. (2006) Roume et al. (1998)
MKS3/TMEM67
8q22.1
MKS4/CEP290/ NPHP6
12q21 MKS5/RPGRIP1L 16q12.2 novel: Frizzled-like receptor, localises to primary cilia & basal bodies centrosomal protein; causative of other ‘ciliopathies’ Smith et al. (2006) Baala et al. (2007) novel: colocalises and interacts with other ciliary proteins Delous et al. (2007)
MKS1 and MKS3 mutations
MKS1
B9 domain
MKS3/Meckelin
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 – accurate diagnosis – confirmation of research results – – carrier testing in at-risk individuals prenatal testing
Proposed test strategy
Referrals to DNA Lab Pakistani origin Screen for common MKS3 splice-site mutations Other origin 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 – –
MKS1
17q22
MKS3
8q22
D17S1853 D8S1818
MKS3
and
D17S1290
and
D8S1699
loci optimised: • 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 MKS1
• c.1451_1453dupGGCA (p.Thr485fs) – Pakistani – 4bp duplication in exon 16
MKS3
• c.1674+1G>A – Pakistani – mutation abolishes exon 16 splice donor site
482 483 484 485 486 487 488 Thr Thr Gly Thr Val Thr Phe Thr Thr Gly Arg His Cys His Exon16 | Intron 16
Upper panel: wild-type Lower panel: homozygous mutant
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
Intron 8 | Exon 9
• c.870-2A>G – Pakistani – mutation abolishes exon 9 splice acceptor site Upper panel: wild-type Lower panel: homozygous mutant
MKS testing costs
Two common Pakistani mutations Microsatellite analysis Sequencing (per gene) Known mutation £200 £100 per person up to £1000 £150 Please contact the laboratory for further information on testing for Meckel-Gruber syndrome.
Acknowledgements
• Leeds Institute of Molecular Medicine Colin Johnson • Yorkshire Regional DNA Laboratory Kim Flintoff, David Cockburn, Ruth Charlton • Yorkshire Clinical Genetics Service Chris Bennett