Case study

1. Case study Wilson Disease Miranda Durkie 2009

2. WD introduction • Autosomal recessive disorder of Cu metabolism • Incidence 1 in 30,000 • Presentation hepatic (usually childhood) or neurological (later age-of-onset) • Treatment by chelating agents very effective if given early • Mutations spread throughout all 21 exons but mutation hot-spots recognised

3. SDGS testing strategy • Analysis by DNA sequencing of 7 out of the 21 exons detects >80% of mutations found in UK population = Stage 1 screen • Rest of gene = Stage 2 screen • Unless specifically says otherwise do St1 only & report results. • Second referral required for St2 analysis

4. Case Study • Affected female, CT, aged 26, fulminant liver failure requiring liver transplant • St1 sequencing found 2 putative mutations p.Ile381Ser + p.Arg723GlufsX32 • p.Ile381Ser novel missense; 5/5 in silico tools predict pathogenic • Reported as “consistent with a diagnosis of Wilson disease” but without functional studies we cannot be certain of significance of p.Ile381Ser

5. Case study cont.1 • Whilst issuing report for CT, samples rec’d from her 2 daughters TM & MM • Referral letter says “Penicillamine challenge info is ambiguous for TM. Whilst this would not be sufficient to make a diagnosis in a symptomatic patient, in a child of 6 years without symptoms we would like to exclude condition genetically” • Asked for father’s sample to test – no reply • After 4 months delay rec’d another letter asking for results for TM & MM • Phone call to clinician

6. Case study cont.2 • Father not available for testing • Unhappy that results were delayed • Did full St1 & St2 screen on the 2 daughters • MM inherited p.Arg723GlufsX32 mutation • TM inherited p.Ile381Ser putative mutation • Found additional missense change in TM p.Ile1184Thr; highly conserved base; 4/5 in silico tools predict pathogenic (not Align GVGD)

7. Case study cont.3 • Difficult to interpret as genotype not seen in affected individual • Report said “as p.Ile381Ser & p.Ile1184Thr putative mutations affect highly conserved bases they are likely to be pathogenic. TM is therefore at risk of developing symptoms of WD” • Case discussed with Consultant Paediatric Hepatologist • Decided to do liver biopsy • Liver biopsy showed levels of Cu in normal range • TM started on zinc treatment

8. Case study cont.4 • Routine family studies showed that grandmother also had same 2 missense changes as TM • Tested affected mother and she also had p.Ile1184Thr putative mutation therefore she has 3 mutations. • Reported to clinicians that p.Ile381Ser & p.Ile1184Thr in cis therefore TM unlikely to be affected • Literature search showed previously reported once in WD in isolated area with very high incidence and founder effect [1]

9. Changes to report templates • Now have also found 2 more cases with 3 mutations • Discussed at WD best practice meeting and other labs reported similar findings but not published • Now reports all state “in light of rare reports[1],[2] of 2 putative mutations occurring on the same ATP7B allele we strongly recommend that xxxxx’s parents or other family members are tested to confirm the observed genotype” • WD EMQN has highlighted this in previous 3 years reports

10. References • [1] Dedousiss GVZ et al (2005) Ann Hum Genet 69: 268-274 • [2] Data from this laboratory & personal communications from EMQN WD best practice meeting, June 2007.

11. Topics for discussion • Full vs partial gene screening • Common or rare phenomena? • Confirmation of genotype in autosomal recessive disorders • Opinion of some clinicians that genetics is conclusive