16 ORIGINAL ARTICLE J Med Genet: first published as 10.1136/jmg.39.1.16 on 1 January 2002. Downloaded from National study of microphthalmia, anophthalmia, and coloboma (MAC) in Scotland: investigation of genetic aetiology D Morrison, D FitzPatrick, I Hanson, K Williamson, V van Heyningen, B Fleck, I Jones, J Chalmers, H Campbell ............................................................................................................................. J Med Genet 2002;39:16–22 We report an epidemiological and genetic study attempting complete ascertainment of subjects with microphthalmia, anophthalmia, and coloboma (MAC) born in Scotland during a 16 year period beginning on 1 January 1981. A total of 198 cases were confirmed giving a minimum live birth preva- lence of 19 per 100 000. One hundred and twenty-two MAC cases (61.6%) from 115 different fami- See end of article for lies were clinically examined and detailed pregnancy, medical, and family histories obtained. A authors’ affiliations simple, rational, and apparently robust classification of the eye phenotype was developed based on ....................... the presence or absence of a defect in closure of the optic (choroidal) fissure. A total of 85/122 Correspondence to: (69.7%) of cases had optic fissure closure defects (OFCD), 12/122 (9.8%) had non-OFCD, and Dr D FitzPatrick, MRC 25/122 (20.5%) had defects that were unclassifiable owing to the severity of the corneal or anterior Human Genetics Unit, chamber abnormality. Segregation analysis assuming single and multiple incomplete ascertainment, Western General Hospital, respectively, returned a sib recurrence risk of 6% and 10% in the whole group and 8.1% and 13.3% Edinburgh EH4 2XU, UK; in the OFCD subgroup. Significant recurrence risks were found in both unilateral and bilateral disease. david.fitzpatrick@ hgu.mrc.ac.uk In four families, one parent had an OFCD, two of which were new diagnoses in asymptomatic subjects. All recurrences in first degree relatives occurred in the OFCD group with a single first cousin recurrence Revised version received seen in the non-OFCD group. A total of 84/122 of the MAC cases were screened for mutations in the 15 October 2001 Accepted for publication coding regions of PAX6, CHX10, and SIX3. No pathogenic mutations were identified in the OFCD 23 October 2001 cases. A single PAX6 homeodomain missense mutation was identified in a subject with partial aniridia ....................... that had been initially misclassified as coloboma. icrophthalmia, anophthalmia, and coloboma (MAC) cases of MAC in children born from 1981-1996 and resident in http://jmg.bmj.com/ are major structural eye malformations. Anophthal- Scotland at birth and to validate cases by examination of Mmia is the complete absence of the eye, microphthal- affected children, where possible. Recognising the clinical mia is a small eye usually defined in terms of corneal diameter heterogeneity in presentation, we also sought to develop and or axial length, and coloboma is a segmental ocular defect, apply a phenotypic classification system based on knowledge most commonly a “keyhole” deficiency in the iris. The best of eye development. Finally, we sought to investigate the pos- estimates of the birth prevalence of microphthalmia and ano- sible role of the most promising candidate genes, the develop- phthalmia from well maintained population based registers mental control genes PAX6, CHX10, and SIX3, in the aetiology on September 28, 2021 by guest. Protected copyright. are 14 and 3 per 100 000 births, respectively. In the last decade of the subgroup of MAC cases with no apparent cause by there has been considerable public concern and media atten- screening selected subjects for germline mutations in these tion aroused by reports of apparent clusters of anophthalmia genes. Homozygous loss of function mutations in PAX6 have and microphthalmia and of possible links between toxic envi- been identified in a single infant with anophthalmia ronmental exposures and these conditions. A number of associated with severe brain abnormalities.5 CHX10 mutations potential environmental causes have been proposed although have been described in two families with non-syndromal 1 the evidence in their support is only preliminary. microphthalmia segregating as an autosomal recessive trait.6 The aetiology of MAC is not well understood. A significant The SIX3 gene underlies some cases of holoprosencephaly7 genetic contribution to the aetiology of non-syndromal MAC with one patient having microphthalmia and coloboma with- has been suggested by previously observed familial clustering out other classical features of holoprosencephaly.7 of these defects2 and successful linkage analysis in a small number of families where these disorders segregate in a Men- METHODS 34 delian fashion. However, there are no published population Case ascertainment based data from which to quantify the relative recurrence risk After ethical approval was obtained from all Local Research in these families. An understanding of the underlying genetic Ethics Committees in Scotland, a national system of case causes of eye defects is necessary for the optimal management ascertainment was established. All MAC cases born in of these conditions, the counselling of the affected families, Scotland between 1981 and 1996 and registered in the and to provide insights into the biological processes involved national congenital anomalies register, the EUROCAT (Euro- in eye development, which in turn may lead to new prevention pean Network of Congenital Anomalies Registers) register in strategies. We aimed to establish a population based and well charac- terised cohort of children with MAC in Scotland to investigate ............................................................. genetic aetiology and improve estimates of recurrence risk for Abbreviations: MAC, microphthalmia, anophthalmia, and coloboma; genetic counselling of affected families. Specific objectives OFCD, optic fissure closure defects; DHPLC, denaturing high performance were to assemble a complete as possible case register of all liquid chromatography; ONC, optic nerve coloboma www.jmedgenet.com National study of MAC in Scotland 17 Table 1 PAX6, CHX10, and SIX3 primers and PCR conditions J Med Genet: first published as 10.1136/jmg.39.1.16 on 1 January 2002. Downloaded from Forward oligonucleotide Reverse oligonucleotide PCR conditions PAX6 Exons 1–13 As in Love et al*AsinLoveet al* except for Exons 1–5a touchdown with 10% DMSO: 95°C, 2 min [94°C, exon 13 1 min; 55–48°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min (5′-TTTTACTGTAATCTTGGCCAG) Exons 6–13: 95°C, 2 min [94°C, 1 min; 53–61°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min SIX3 5′UTR/CDS 5′-AAATGTTTCAATGCTGCACTC 5′-GGAGCGGTGGTGAGAATC 10% DMSO: 94°C, 4 min [98°C, 45 sec; 53°C, 1 min; 72°C, 3 min]×40; 72°C, 5 min SIX domain 5′-CTAGACCTCTATTCCTCCC 5′-CTCAAGGATGTGGTAGAGG 10% DMSO: 95°C, 2 min [94°C, 1 min; 53°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min SIX/homeodom 5′-GTGGTCGCCTTCCACACG 5′-CTTCCCAGGCCTCTGAGGC 10% DMSO: 95°C, 2 min [94°C, 1 min; 55°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min CDS/3′UTR 5′-GTGGCGGGCCTCTGTGTC 5′-TTTGGCTGGGGTGGGAGTG 10% DMSO: 94°C, 4 min [98°C, 45 sec; 57°C, 1 min; 72°C, 3 min]×40; 72°C, 5 min 3′UTR 5′-CGAAATCAGGATACCCAACC 5′-CGGAACGGAGACGGCGAC 10% DMSO: 95°C, 2 min [94°C, 1 min; 54°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min CHX10 Exons 1–5 As in ref 6 As in ref 6 Exon 1 touchdown with 10% DMSO: 95°C, 2 min [94°C, 1 min; 67–63°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min Exons 2–5: 95°C, 2 min [94°C, 1 min; 63–65°C, 1 min; 72°C, 1 min]×40; 72°C, 10 min *Love et al. Hum Mutat 2000;12:128-34. PCR reagents were essentially as described in Love et al, except the polymerase used was AmplitaqGold (Amersham) supplemented with cloned Pfu (Stratagene). Greater Glasgow, and the register of the blind and the national consanguineous (first cousin) parents. Two different segrega- blind school were identified. In addition, all paediatricians, tion analyses were performed, (1) assuming single incomplete clinical medical officers, Directors of Public Health, Directors ascertainment8 and (2) assuming multiple incomplete of Education, clinical geneticists, community paediatricians, analysis.910 For detailed discussion of the limitations of both paediatric pathologists, ophthalmologists, and ophthalmic approaches see Smith.11 prosthetic departments in Scotland and the national patient support group were contacted with a request to them to notify cases to us. The completeness of case ascertainment was esti- Sample collection and mutation analysis mated by log linear modelling (capture recapture techni- After written consent was obtained, DNA was prepared from que).The decision to include a case in the study was on the samples collected either by venepuncture after application of basis of a confirmed primary ophthalmic diagnosis of MAC by local anaesthetic cream (preferred method) or exfoliated buc- an experienced ophthalmologist. cal cells (where permission for venepuncture was not given). http://jmg.bmj.com/ With the consent of the parents and/or child, each case was Purified genomic DNA was used as a template to amplify the reviewed by the study ophthalmologist and a full ophthalmic exonic sequences (including intron-exon boundaries) con- (including slit lamp and ultrasound examinations) and taining the open reading frame of PAX6, CHX10, and SIX3 using dysmorphological assessment (including a series of photo- primers and PCR conditions detailed in table 1. Following graphs and clinical measurements) was carried out. Clinical amplification, mutation analysis was carried out using findings were reviewed by consultants in ophthalmology and denaturing high performance liquid chromatography clinical genetics. In cases in whom examination was not pos- (DHPLC).12 If a shifted DHPLC peak was evident, the original sible, the medical records of the child were reviewed. We found DNA sample was reamplified and sequenced.