Genetic disease –taking samples

1. Genetic disease –taking samples Bill Newman St Mary’s Hospital May 2008

2. .. so what can we really test for?

3. Genetic Disease • Chromosomal=6 per 1000 LB • Aneuploidy • Structural abnormalities • DNA/single gene=13 per 1000 LB • Mendelian inheritance • Non-Mendelian inheritance • Multifactorial e.g CL/CP,NTD,cancer • Susceptibility genes • Environmental influences eg drugs

4. Chromosomal disease Can identify large chromosomal changes – >4Mb Culture leukocytes – dividing cells with long chromosomes

5. When to do a chromosomal test • Prenatal: maternal age>37yrs; USS changes; Family history Triple test = increased risk • Postnatal: Learning & developmental disability; growth retardation • Infertility: Recurrent miscarriage, primary infertility

6. Prenatal Diagnosis Chorionic villus biopsy >10/40 Miscarriage 1% Results :~1 week Amniocentesis >14/40 Miscarriage 0.5% Results :~3 weeks

7. Aneuploidy • Autosomal: • Trisomy 21 (Down syndrome) • Trisomy 18 (Edward syndrome) • Trisomy 13 (Patau syndrome) • Sex chromosome: • 47XXY (Klinefelter syndrome) • 45X (Turner syndrome)

8. Trisomy 21 1 in 600 livebirths Learning disability Congenital heart defects Duodenal atresia Macroglossia Brachycephaly Epicanthic folds Brushfield spots

9. Trisomy 13 1 in 10,000 livebirths Holoprosencephaly, Polydactyly Flexion of the fingers facial clefting heart defects Scalp defects Microcephaly Polycystic kidneys

10. Trisomy 18 1 in 3,000 livebirths Neurodevelopmental delay Flexion of the fingers coloboma heart defects Microcephaly Horseshoe kidney

11. Turner syndrome 45 X

12. Klinefelter syndrome 47, XXY

13. Rapid Aneuploidy Screening by FISH • Available on amniocentesis sample • Uncultured amniocytes • FISH probes for X,Y, 21,18,13 • Result in 24-48 hours • Proceed onto full karyotype (11-14 days)

14. FISH analysis Normal two copies of chromosome 18 in male

15. New techniques • qf (quantitative) PCR – able to measure number of copies of a chromosome – used for trisomy screening • Fetal DNA – at 6-8 weeks to determine sex – look for presence of Y chromosome material

16. Structural Chromosome Abnormalities • De novo (spontaneous) or inherited • Deletion:visible cytogenetically eg 5p- • Microdeletion:use FISH eg William’s Syndrome

17. Array Comparative Genomic Hybridisation (aCGH) • New technique – identifies subtle chromosome deletions/duplications • Detects changes in ~25% children with learning difficulty + dysmorphism and normal chromosomes

18. Mosaicism • Mixed population of normal/abnormal karyotype • May affect some tissues • Karyotype from skin biopsy • Skin pigmentation • Growth distortion

19. Reciprocal Translocation • Balanced exchange of genetic material between chromosomes • Can result in unbalanced gametes • recurrent miscarriage • fetal abnormality • liveborn with structural defects + dysmorphism + MR

20. Reciprocal Translocation Balanced translocation Normal Normal Balanced Dup/del Dup/del

21. Molecular genetic testing • Diagnostic – to confirm diagnosis • Predictive/presymptomatic – predict future illness • Carrier screening – reproductive risk

22. Risk estimation in genetics • Inherited disease: • Autosomal dominant e.g. NF1, HD, Marfan • Autosomal recessive e.g. CF • X-linked recessive e.g. Duchenne MD • mitochondrial e.g. Lebers optic atropy • chromosomal e.g. translocations, • Complex disease e.g. asthma, • autoimmune disease

23. Autosomal Dominant e.g. Huntington’s Disease Anticipation Trinucleotide repeat expansion 50% - dependent upon age ?

24. Autosomal Dominant • Neurofibromatosis type I • Pigmented skin lesions: café au lait spots • Neurofibromata • Axillary freckling • Macrocephaly • Learning difficulties • Variable phenotype even within a family

25. Neurofibromatosis type 1

26. Neurofibromatosis type 1 50%?? New mutation?? Examine parents No signs = New mutn a few ? Mosaic 1-2% definite NF1 50% Examine child if >6 and not affected then ok ?

27. Autosomal Recessive ‘My brother’s child has cystic fibrosis’ ‘My wife is pregnant’ ‘Will our child have cystic fibrosis?’

28. Cystic fibrosis Most common AR genetic disease in UK Caucasian population Carrier frequency 1/25 Many different mutations (>700) Common mutation DF508 (3bp deletion) Lung disease GI Disease (meconium ilieus/pancreatic insufficiency) Infertility in males Survival increasing >35yrs Genetic testing available Prenatal diagnosis available

29. Cystic fibrosis 1/25 1/2 1/25 X 1/2 X 1/4 = 1/200

30. - - + - - - - - + - - - - - - - + - + - - - - - DF508 G85E R117H 621+1 G>T G551D R553X G542X 1154insTC Cystic fibrosis- genetic tests 1/25 1/2

31. - - + - - - - - + - - - - - - - + - + - - - - - DF508 G85E R117H 621+1 G>T G551D R553X G542X 1154insTC Cystic fibrosis 1/25 1 + - - - - - - - 1/25 X 1 X 1/4 = 1/100

32. - - + - - - - - + - - - - - - - + - + - - - - - DF508 G85E R117H 621+1 G>T G551D R553X G542X 1154insTC Cystic fibrosis 1/160 1 - - - - - - - - + - - - - - - - 1/160 X 1 X 1/4 = 1/640

33. X-linked recessive • No male to male transmission • Males affected • Females usually unaffected carriers (except skewing) • Affected male: all daughters are carriers, no sons affected • Carrier female: 50% risk affected son, 50% risk carrier daughter • eg DMD/BMD, haemophilia

34. X Linked recessive inheritance Is the mother a carrier for condition – confirmed if recurrence, by genetic or other tests If the mother is not a carrier for condition – lower risk of recurrence and no risk to other family members

35. GOOD LUCK!