PURPOSE Congenital cataract is a significant cause of blindness worldwide. Many genes are known to cause the disorder. A large multigenerational pedigree was investigated for the genetic cause of a posterior polar autosomal dominant congenital cataract. METHODS A genome wide scan was conducted in a large multigenerational family with autosomal dominant cataract to identify the linked region of the genome. The PITX3 gene was investigated through direct sequencing and detection of fluorescently labeled PCR products. RESULTS Linkage was detected to a region of chromosome 10q23-26 which contains the candidate gene PITX3. A segregating 17 bp insertion mutation was identified. This mutation was not identified in 100 additional unrelated sporadic and familial congenital cataract patients. No mutations of the PITX3 gene were identified in 9 families with posterior polar congenital cataract. CONCLUSIONS The 657ins17bp duplication of the PITX3 gene is the cause of the cataract phenotype in the large pedigree, however, this gene appears responsible for only a small proportion of congenital cataract in Australia.

AIMS:Multiple genetic causes of congenital cataract have been identified, both as a component of syndromes and in families that present with isolated congenital cataract. Linkage analysis was used to map the genetic locus in a six generation Australian family presenting with total congenital cataract.METHODS:Microsatellite markers located across all known autosomal dominant congenital cataract loci were genotyped in all recruited family members of the Tasmanian family. Both two point and multipoint linkage analysis were used to assess each locus under an autosomal dominant model.RESULTS:Significant linkage was detected at the telomere of the p arm of chromosome 1, with a maximum two point LOD of 4.21 at marker D1S507, a maximum multipoint exact LOD of 5.44, and an estimated location score of 5.61 at marker D1S507. Haplotype analysis places the gene inside a critical region between D1S228 and D1S199, a distance of approximately 6 megabases. The candidate gene PAX7 residing within the critical interval was excluded by direct sequencing in affected individuals.CONCLUSION:This is the third report of congenital cataract linkage to 1ptel. The critical region as defined by the shared haplotype in this family is clearly centromeric from the Volkmann cataract locus identified through study of a Danish family, indicating that two genes causing autosomal dominant congenital cataract map to the telomeric region of chromosome 1p.

Aims: Mutations of seven crystallin genes have been shown to cause familial cataract. The authors aimed to identify disease causing crystallin mutations in paediatric cataract families from south eastern Australia.Methods: 38 families with autosomal dominant or recessive paediatric cataract were examined. Three large families were studied by linkage analysis. Candidate genes at regions providing significant LOD scores were sequenced. Single stranded conformational polymorphism (SSCP) analysis was used to screen five crystallin genes in the probands, followed by direct sequencing of observed electrophoretic shifts. Mutations predicted to affect the coding sequence were subsequently investigated in the entire pedigree.Results: A LOD score of 3.72 was obtained at the gamma-crystallin locus in one pedigree. Sequencing revealed a P23T mutation of CRYGD, found to segregate with disease. A splice site mutation at the first base of intron 3 of the CRYBA1/A3 gene segregating with disease was identified by SSCP in another large family. Five polymorphisms were also detected.Conclusions: Although mutations in the five crystallin genes comprehensively screened in this study account for 38% of paediatric cataract mutations in the literature, only two causative mutations were detected in 38 pedigrees, suggesting that crystallin mutations are a relatively rare cause of the cataract phenotype in this population.

Congenital or paediatric cataract is a phenotypically and genetically heterogeneous disorder consisting of lens opacities in early life. Thirteen genes have been described for autosomal dominant congenital cataract (ADCC). These include genes for seven members of the crystallin family,1,2 which are responsible for the refractive index and transparency of the lens, two connexin genes3,4 and major intrinsic protein of the lens (MIP)5 which are involved in the transport directly between cells of small metabolites and water, respectively, the cytoskeletal protein beaded filament structural protein-2 (BFSP2),6 and transcription factors paired-like homeodomain transcription factor-3 (PITX3)7 and heat shock factor-4 (HSF4).8 Five additional loci have been described on chromosomes 1pter-p36.1,9 15q21-q22,10 17p13,11 17q24,12 and 20p12-q12.13 We used a linkage approach to investigate these 13 genes and five loci in a large pedigree from Victoria, Australia, with zonular pulverulent cataract with the aim of identifying the causative mutation. Ethics approval for this study was obtained from the Human Research Ethics Committees of the Royal Children’s Hospital, Melbourne, Australia, the Royal Victorian Eye and Ear Hospital, Melbourne, Australia, and the University of Tasmania, Hobart, Australia. ### Patient ascertainment and collection of genetic material The pedigree crch13 was identified through a database maintained by the Royal Children’s Hospital, Melbourne, Australia and the Royal Victorian Eye and Ear Hospital, Melbourne, comprising paediatric cataract patients from south-eastern Australia with any type of lens opacity.14 Written informed consent was obtained from all participating individuals or their guardians. When possible, family members were examined by one or more ophthalmologists (MGW, DAM, JEE, JEC, or IR-E). Due to the rural location of most family members, affection status was determined from medical records when direct examination was not feasible. In many cases pre-operative visual acuity was not available. Buccal mucosal swabs were either collected during examination …

Nance-Horan syndrome (NHS) is an X-linked disorder characterized by congenital cataracts, dental anomalies, dysmorphic features, and, in some cases, mental retardation. NHS has been mapped to a 1.3-Mb interval on Xp22.13. We have confirmed the same localization in the original, extended Australian family with NHS and have identified protein-truncating mutations in a novel gene, which we have called "NHS," in five families. The NHS gene encompasses approximately 650 kb of genomic DNA, coding for a 1,630-amino acid putative nuclear protein. NHS orthologs were found in other vertebrates, but no sequence similarity to known genes was identified. The murine developmental expression profile of the NHS gene was studied using in situ hybridization and a mouse line containing a lacZ reporter-gene insertion in the Nhs locus. We found a complex pattern of temporally and spatially regulated expression, which, together with the pleiotropic features of NHS, suggests that this gene has key functions in the regulation of eye, tooth, brain, and craniofacial development.

Background/aim: Paediatric cataract is a major cause of childhood blindness. Several genes associated with congenital and paediatric cataracts have been identified. The aim was to determine the incidence of cataract in a population, the proportion of hereditary cataracts, the mode of inheritance, and the clinical presentation. Methods: The Royal Children's Hospital and the Royal Victorian Eye and Ear Hospital have a referral base for almost all paediatric patients with cataracts in south eastern Australia. The database contains cases seen over the past 25 years. The medical histories of these patients were reviewed. Results: 421 patients with paediatric cataract were identified, which gives an estimated incidence of 2.2 per 10 000 births. Of the 342 affected individuals with a negative family history, 50% were diagnosed during the first year of life, and 56/342 (16%) were associated with a recognised systemic disease or syndrome. Unilateral cataract was identified in 178/342 (52%) of sporadic cases. 79 children (from 54 nuclear families) had a positive family history. Of these 54 families, 45 were recruited for clinical examination and DNA collection. Ten nuclear families were subsequently found to be related, resulting in four larger pedigrees. Thus, 39 families have been studied. The mode of inheritance was autosomal dominant in 30 families, X linked in four, autosomal recessive in two, and uncertain in three. In total, 178 affected family members were examined; of these 8% presented with unilateral cataracts and 43% were diagnosed within the first year of life. Conclusions: In the paediatric cataract population examined, approximately half of the patients were diagnosed in the first year of life. More than 18% had a positive family history of cataracts. Of patients with hereditary cataracts 8% presented with unilateral involvement. Identification of the genes that cause paediatric and congenital cataract should help clarify the aetiology of some sporadic and unilateral cataracts.