SP17

Suspected confined blood chimerism in monochorionicdizygotic (MCDZ) twins

or

Twin-Twin confusion syndrome

David GokhaleMolecular Genetics Laboratory

Liverpool Women’s Hospital

Summary

• Brief reminder about twinning etc.

• Reproductive and Obstetric history

• Neonatal History

• Molecular and cytogenetic analysis

• Conclusions and discussion

From Hall, J.G., Twinning, Lancet 2003; 362: 735–43

Definitions

• Mosaicism

The presence in an individual or tissue of at least two cell lines differing in genotype or karyotype, but derived from one zygote.

• Chimerism

The presence of cells from two genetically distinct sources (e.g. transplant, graft or embryo fusion).

From Hall, J.G., Twinning, Lancet 2003; 362: 735–43

Reproductive and Obstetric history

• Conceived by IVF

• Antenatal ultrasound (USS) at a local district general hospital showed a twin pregnancy and a monochorionic, diamniotic placenta

• Antenatal steroids given following premature rupture of membranes on twin 2 noted at 24+2 weeks gestation.

Delivery

• Twins delivered by emergency c-section at 25+1 weeks gestation– Twin 1: Phenotypically Male, 710 grams– Twin 2: Phenotypically Female, 740 grams

• Both twins required resuscitation, intubation and surfactant before being transferred to the Neonatal Unit at LWH.

Neonatal History – Twin 1 (male)

• Better condition at birth

• Respiratory difficulties

– ventilated for 39 days in total– chronic lung disease

• many “near death” experiences

HR = 60

SaO2 = 40

Time = 10 mins

• Transfusions x9

• Laser treatment for retinopathy of prematurity carried out 6th August

• Home day = 142, term + 5 weeks

Neonatal History – Twin 1 (male)

• Poorer condition at birth

• better respiratory outcome– 36 days ventilation– chronic lung disease – weaned off oxygen before discharge

• less “near death” experiences

Neonatal History – Twin 2 (female)

• Transfusions x8

• Laser treatment for retinopathy of prematurity carried out 6th August

• Home day 118, term + 1 week

Neonatal History – Twin 1 (female)

Referral

• Discrepancy between USS findings and twin’s gender raised by the parents approx 4 weeks later

• Placental histology confirmed monochorionic diamniotic placenta

• Samples then taken for genetic analysis

X and Y chromosome microsatellite analysis

Male Twin

Female Twin

Analysis of initial blood samples

DYS448DXS6803 DXS981

DYS448DXS6803 DXS981

Subsequent Investigations

• Buccal swabs taken from both twins

• Female twin (twin 2)– abdominal USS showed normal uterus– endocrine and thyroid investigations normal– thyroid function normal

• Male twin (twin 1)– endocrine & thyroid investigations normal– hernia repair scheduled with tissue sampling (risk of

gonadoblastoma)

Analysis of buccal cell samples

Male Twin

Female Twin

DYS448DXS6803 DXS981

DYS448DXS6803 DXS981

Male Twin – Analysis of hernial sac & inguinal skin

Uncultured

Cultured

DYS448

DYS448

DXS6803

DXS6803 DXS981

DXS981

Cytogenetic analysis

• No cells detected in any tissues with XXY

• Blood sample FISH analysis (DXZ1 & SRY): – Male twin (95% XX, 5% XY)– Female twin (88% XX, 12% XY)

• Analysis of cultured cells from hernial sac and inguinal skin only detected presence of XY cells in male twin

Conclusions

• Our findings are suggestive of chimerism limited to blood

• Possible mechanisms (Williams et al. 2004)– Placental vascular anastomoses (after the development of

haematoblast stem cell lines) or– Admixture of trophoblast cells during early blastocyst development

(restricted to the extra-embryonic tissues)

• Only been 10 case reports (the earliest being 1977) of blood chimerism in dizygotic twins of opposite genders

Discussion

• Up to 8% of dizygotic twins have been noted to have some evidence of blood chimerism (van Dijk, et al.)

• Has IVF increased the likelihood of embryo fusion due to proximity ?

• Is the apparent chimerism likely to persist and for how long?

Acknowledgements

• Julie Sibbring (Molecular Genetics, LWH)• Frances White (Molecular Genetics, LWH) • Aram Buchanan (Cytogenetics, LWH)• Magda Ainscough (Cytogenetics, LWH)• Dan Hawcutt (SpR & Lecturer in Paediatric Pharmacology,

LWH)• Leanne Bricker (Consultant Obstetrician, LWH)• Family ‘G’