68868 Med Genet 1997;34:688-691 Monozygotic twins discordant for Aicardi

syndrome J Med Genet: first published as 10.1136/jmg.34.8.688 on 1 August 1997. Downloaded from

T Costa, W Greer, G Rysiecki, J R Buncic, P N Ray

Abstract be dizygotic,' while zygosity was not indicated Aicardi syndrome is a developmental dis- in the fourth pair.8 We describe here two young order characterised by agenesis of the women who were shown conclusively to be corpus cailosum, retinal lacunae, sei- monozygotic twins who are discordant for zures, and developmental delay. It is Aicardi syndrome. believed to be X linked with lethality in males. We report a set of monozygotic female twins one of whom is healthy and Case report intellectually normal while the other has The 19 year old twins were the product of the the classical Aicardi phenotype with pro- fifth and last pregnancy of healthy, non- found retardation. Family history is nega- consanguineous parents of mixed European tive. Both had normal karyotypes. extraction. Of the other four children, two boys Departments of and two girls, three were in good health. One of Genetics and Monozygosity was established by blood chromosomal heteromor- the sons died at the age of 4 months Pediatrics, The grouping, of sudden infant death syndrome. Hospital for Sick phisms, and DNA analysis using six presumably Children, and hypervariable probes (five autosomal and The oldest daughter had pyloric stenosis in Department of one X linked) and three X linked RFLP infancy requiring surgical correction. The Pediatrics, University We the hypothesis that mother was 34 years of age at the time of deliv- ofToronto, Canada probes. tested ery while the father was 39. The pregnancy was T Costa preferential inactivation of a different X normal with the exception of a flu-like illness chromosome had occurred in each girl. and vaginal spotting of a few days duration in Department of Methylation sensitive RFLP analysis of Pathology, Victoria DNA from EBV transformed B lym- the first trimester. Delivery was at term. The General Hospital, phocytes and cultured skin fibroblasts proband, twin 1, was delivered by vertex Dalhousie University, vaginal route without complications. Her twin Halifax, Canada using MspVIHpaII digestion and probing was delivered in breech. Birth weight was 3080 W Greer with M27P showed a very similar pattern g for twin 1 and 3420 g for twin 2. There was a ofX inactivation in both twins with no evi- single placenta with two separate cords. Departmnent of dence of preferential expression of one http://jmg.bmj.com/ Genetics, The Hospital Findings on microscopic examination of the particular . We conclude were of a dichorionic for Sick Children, that the abnormalities in the affected twin membranes suggestive Toronto, Canada of a gestation. G Rysiecki* are probably the consequence postzy- Twin 2 has been in good health and has had gotic in early embryonic devel- normal pyschomotor development. The Department of opment. proband is patient 14 in the series described by Ophthalmology, The (7Med Genet 1997;34:688-691) Hospital for Sick Menezes et al.'° She was noted to have Children and Keywords: Aicardi syndrome; monozygotic twins; dis- unilateral microphthalmos in the newborn on September 29, 2021 by guest. Protected copyright. University ofToronto, cordant; X linked inheritance period. activity was first recognised at Toronto, Canada the age of 2'/2 months and has been a persist- J R Buncic ent problem despite anticonvulsant medi- Aicardi is a disorder cation. A retinal detachment was noted in the Departments of syndrome developmental Genetics and Pediatric characterised by agenesis of the corpus callo- right microphthalmic eye at the age of 8 years. Laboratory Medicine, sum, , developmental delay, and dis- Her psychomotor development has been pro- The Hospital for Sick tinctive chorioretinal abnormalities described foundly delayed. She has not acquired any Children, and as "lacunae". Since it was first reported by speech and remains wheelchair bound. She Department of Aicardi et all in 1965, nearly 200 cases have recognises members of the family and reaches Molecular and Medical been reported,2 all females with the exception for objects, suggesting that she does have some Genetics, University of was Toronto, Toronto, of one male with a 47,XXY karyotype.3 This is vision. A diagnosis of Aicardi syndrome Canada suggestive ofX linked inheritance with lethality made at the age of 8 months on the basis of P N Ray in males. Tentative mapping of the gene has typical retinal abnormalities on fundoscopic been made to the Xp22 region based on an examination and the finding of agenesis of the Correspondence to: affected female with an apparently balanced on pneumoencephalogram. Dr Costa, Division of Clinical Genetics, The X;3 translocation with a breakpoint through On examination at the age of 17 years, the Hospital for Sick Children, Xp22.4 As expected for a dominant mutation proband presented as a profoundly retarded 555 University Avenue, with poor reproductive fitness, almost all cases young woman. The head circumference was 51 Toronto, Ontario, Canada have been sporadic. The one exception, in two cm (<2nd centile). The occiput was flat. There M5G 1X8. with *Present address: Cellmark daughters of healthy, non-consanguineous was facial asymmetry right microphthal- Diagnostics, Oxforshire, UK. parents,5 can be explained by germline mosai- mia, a right facial hemiatrophy, and prominent cism in one of the parents. Seven twin pairs right auricle. There was a maxillary overbite. Received 28 October 1996 6-9 a with Revised version accepted for have been reported2 and all were discordant. There was left spastic hemiparesis publication 3 March 1997 Of the four girl-girl pairs, three were known to flexion contractures of the fingers, knee, and Aicardi syndrome 689

hip. However, she was hyporeflexive, especially HpaII, which recognises the same restriction on the right. There was ankle clonus and a site as MspI, but only when the site is not bilateral Babinski sign. Ocular examination methylated. These samples were then size frac- showed a microphthalmic right eye, the fundus tionated, transferred to nylon membranes as J Med Genet: first published as 10.1136/jmg.34.8.688 on 1 August 1997. Downloaded from ofwhich could not be visualised. In the left eye, described above, and probed with 32P labelled the anterior segment and lens were normal. M27P. The fundus had numerous lacunae surround- Six hypervariable probes for markers on six ing the disc (fig 1) but the macula appeared different chromosomes were used to establish intact. She followed light and reached for the zygosity of the twins. The probes were objects. An MRI of the head showed complete 3'HVR,"2 YNH24, JC23. 1, CMM86, absence of the corpus callosum. The septum EFD64.2," and M273. 14 X linked RFLP pellucidum was present in the midline. The probes include 782," GMGX9,16 and XJ1.1.'7 ventricles were large and misshapen secondary to associated parenchymal atrophy. The right Results orbit enclosed a microphthalmic eye with Chromosome studies on peripheral blood evidence of the sequelae of the previous retinal using G banding techniques were normal in detachment. both twins. The parents and twins were further studied using solid staining, Q banding, and C Materials and methods banding. The family was informative for Blood was collected from the twins, both heteromorphisms at C-i qh, C-9qh, Q-13 cent, parents, and a brother and a sister. A skin and Q-21 sat. Both twins showed identical pat- biopsy was done on each twin in the deltoid terns. The family was informative for blood region. Chromosomes were studied using G groups Rh and MNSS, the father being cde/cde and C banding, solid staining, and prophase and NNss, and the mother CDe/CDe and banding on blood lymphocytes. Blood groups MNSs. The twins were both CDe/cde and (ABO, Rh, MNSs, and Lewis systems) were NN/ss. The twins showed identical patterns analysed by standard techniques. with all six of the hypervariable probes tested. Total genomic DNA was extracted from Taking into account the prior probability that EBV transformed lymphoblastoid cell lines the twins are monozygotic (1/3) as well as the and from cultured skin fibroblasts. For zygosity blood group, cytogenetic, and molecular data, determination and X chromosome segregation the probability that they are monozygotic is analysis, DNA samples (3 jg) were digested to greater than 99%. completion with the appropriate restriction X linked probes from the putative Aicardi endonucleases, size fractionated on 0.6% agar- region, Xp2 1-22, were used to study X ose gels, and transferred to nylon membranes segregation in this family. The mother was (Amersham, Hybond) by Southern blotting. X found to be heterozygous at three of the loci chromosome inactivation studies were con- tested. All four of the children inherited this ducted using the probe DNA samples region from the same maternal X chromosome

M27Pf." http://jmg.bmj.com/ (9 gg) were predigested with restriction endo- (data not shown). In spite of having inherited nuclease PstI. A 3 gg aliquot was further the same maternal X chromosome as the digested with MspI. A second aliquot was proband, the brother and two sisters are unaf- digested with the methylation sensitive enzyme fected. Results of X chromosome inactivation stud- ies in EBV transformed lymphoblastoid cell lines are summarised in fig 2. The MspIIHpaI sites flanking the DXS255 locus are extensively on September 29, 2021 by guest. Protected copyright. methylated on the active X chromosomes and unmethylated on inactive X chromosomes. Therefore, the M27,B probe that binds to this locus can be used to differentiate between the active and inactive X through methylation pat- terns shown by MspI and its methylation sensi- tive isoschizomer, HpaII.'4 The patterns are similar in both twins; the unaffected twin shows equal proportions of active and inactive paternally derived X chromosomes while the affected twin shows slight skewing towards inactive. Neither case shows any evidence of exclusive expression of one particular X chromosome. Identical results were observed in cultured skin fibroblasts. Discussion Phenotypic variations and even discordance for genetic traits have been well documented in monozygotic twins.'8 Several genetic, epige- netic, and environmental factors may account for this phenomenon. Postzygotic with resultant somatic mosaicism probably Figure Retinalfindings in the proband (left eye). occur commonly in singletons.'9 In twins, a 690 Costa, Greer, Rysiecki, Buncic, Ray

might therefore be at risk for having an affected child. Accordingly the elucidation of the molecular basis for Aicardi syndrome will be invaluable in counselling this young woman J Med Genet: first published as 10.1136/jmg.34.8.688 on 1 August 1997. Downloaded from about her reproductive options. The relevance ofX inactivation studies in the twins reported here depends on the validity of the hypothesis that the disease is X linked. The .. jr il. I-i J' ) IrjrkLf ;.'.! evidence for this, in fact, is not compelling. In _females heterozygous for some X linked disor- A - sli". 048 a MP ders, selection against or favouring the muta- tion will lead to apparent skewing of X * * ** v inactivation, as has been shown for incontinen- tia pigmenti.2 The results of X inactivation studies in Aicardi syndrome have been incon- clusive. Of the nine cases investigated to date, the twin described here and eight unrelated W~~~~~~~~~~~~~~~~~~~~~~~~...... singletons,- 30 only three were shown to have Figure 2 RFLP methylation analysis using the priobe M27/B is shown for the Aicardi non-random inactivation. Furthermore, the kindred, an obligate carrier of Wiskott-Aldrich syndirome, and a normalfemale control inactivation pattern correlated poorly with the subject. X chromosome inactivation patterns are shonwn below the correspondingfamily phenotype.30 Chromosome studies similarly members. DNA samples from EBV transformed B cells were digested with PstI (P), PstI have not been very fruitful. There is a striking plus MspI (M), or PstI plus HpaII (H). Heterozygosity was detected in allfemales upon digestion with PstI. Further digestion with HpaII reiduced the size ofonly a portion ofeach paucity of karyotypically abnormal girls with band in the normal control. By contrast, the obligate carrier of Wiskott-Aldrich syndrome, the syndrome. The only two cases reported had who is known to exhibit non-random X inactivationa in lymphoid cells,"5 shows the upper atypical fndings. One patient with an X;3 band remaining undigested, and the lower band completely digested. None of the females in this pedigree show non-random restriction patterns I!ike that of the Wiskott-Aldrich translocation had agenesis of the corpus callo- syndrome carrier. A restriction map of the DXS255,'locus is shown at the bottom, indicating sum, vertebral anomalies, and right the region ofM27/B hybridisation. The shaded area represents a polymorphic repeat segment microphthalmiai However, the fundoscopic in which the number of repeats varies from chromosome to chromosome. Restriction sites are were There were of indicated: PstI (P), MspI (M), EcoRI (E), and BacmHI (B). findings atypical. clumps retinal pigment and pin head sized whitish postzygotic mutation after cleavage would be areas but no large depigmented lacunae. This expected to lead to complete discordance, picture is strikingly similar to that reported by while mutation occurring before or during the Donnenfeld et arl in a girl with Xp22-pter who twinning processs could lead to variable degrees initially had been described as having Aicardi of mosaicism aind differing phenotypes. Sur- syndrome but, on further review, was judged prisingly, to d&ate, mosaicism has only been not to meet the diagnostic criteria for Aicardi documented ira one twin pair which was syndrome.32 The phenotype described for sev- discordant for facioscapulohumeral muscular eral other cases of deletion Xp22 appears to be dystrophy (FSEID) and showed different diges- a distinct syndrome, labelled by some authors http://jmg.bmj.com/ tion patterns ait a restriction site within the as MLS or MIDAS syndrome.33The disorder is FSHD gene.20 Another possible cause of characterised by microphthalmia and linear discordance, at least in female pairs, is skewed skin defects. Some affected children have had X inactivation, with one twin showing prefer- agenesis of the corpus callosum and chorioreti- ential expressic)n of one X chromosome and nal lesions, but none has had the typical the other twin sshowing expression of the other stigmata of Aicardi syndrome. MLS may well

X chromosomee. There are now several well be a contiguous gene syndrome encompassing on September 29, 2021 by guest. Protected copyright. documented e:xamples of this phenomenon the Aicardi gene, but the differences in occurring in a variety of X linked disorders ophthalmological presentation may indicate including Duc:henne muscular dystrophy,21 that the two disorders are unrelated. We red-green colouir blindness,22 Hunter disease,23 suggest that the assignment ofthe Aicardi locus and .24 In the family to the X chromosome therefore is premature. described here, studies using peripheral lym- The occurrence of the disorder in females can phocytes showred random X inactivation.25 also be explained by an autosomal gene with Since the twin s had shared a single placenta male lethality as argued by Migeon et ar4 for with a high likelihood of vascular . Future searches for the Aicardi connections,26 we obtained skin fibroblasts for gene should not focus solely on Xp22. further studies The results were identical. This, of course , does not rule out skewed X We are grateful to Dr I Teshima, director of the cytogenetic laboratory at The Hospital for Sick Children, for doing the inactivation in 1the central nervous system, the chromosome studies. tissue primarilyr involved in Aicardi syndrome, since different tissues might show different 1 Aicardi J, Lefevre J, Lerique-Koechlin A. A new syndrome: patterns of X inlactivation." However, the most spasms in flexion, callosal agenesis, ocular abnormalities. Electoencephalogr Clin Neurophysiol Suppl 1965;19:609-10. likely explanati(on for the findings in this family 2 Chevrie JJ, Aicardi J. The Aicardi syndrome. In: Pedley TA, is a mitotic muitation in the affected girl after Meldrum BS, eds. Recent advances in epilepsy. Vol 13. could have Edinburgh: Churchill Livingstone, 1986:189-210. twinning. Alter:nately the mutation 3 Hopkins U, Humphrey I, Keith CG, et al. The Aicardi syn- occurred befo:re or with drome in a 47,XXY male. Aust PaediatrJ 1979;15:278-80. during twinning of to two 4 Ropers HH, Zuffardi 0, Bianchi E, Tiepolo L. Agenesis unequal allocat.ion of mutated cells the the corpus callosum, ocular, and skeletal anomalies embryos. The lxast scenario raises the (X-linked dominant Aicardi's syndrome) in a girl with bal- possibility Hum Genet a small anced X/3 translocation. 1982;61:264-8. that the unaffected twin might have 5 Molina JA, Mateos F, Merino M, et al. Aicardi syndrome in proportion of cells with the mutation and two sisters. I Pediatr 1989;115:282-3. Aicardi syndrome 691

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