Predictive genetic testing in minors for Myocilin juvenile onset open angle glaucoma.

Myocilin glaucoma is an autosomal dominant disorder leading to irreversible blindness, but early intervention can minimize vision loss and delay disease progression. The purpose of this study was to discuss the benefits of predictive genetic testing in minors for Myocilin mutations associated with childhood onset glaucoma. Three families with Myocilin mutations associated with an age of onset before 18 years and six unaffected at-risk children were identified. Predictive genetic testing was discussed with the parents and offered for at-risk minors. Parents opted for genetic testing in half of the cases. None carried the familial mutation. The age of disease onset in the family, the severity of the condition, and the age of the child are all factors that appear to influence the decision of the parent to test their children. Predictive genetic testing for early onset Myocilin glaucoma can facilitate early detection of disease or discharge from routine ophthalmic examinations.

Dissecting the loci controlling fetal haemoglobin production on chromosomes 11p and 6q by the regressive approach.

The changes in the type of haemoglobin (Hb) produced during embryonic, fetal and adult life, have served as a paradigm for understanding the developmental regulation of human genes. A genetically determined persistence of fetal Hb synthesis has an ameliorating effect on beta thalassaemia and sickle cell anaemia, globally the commonest single gene disorders. The search for the putative gene(s) controlling the level of fetal Hb production has been extremely difficult because this trait may be influenced by several factors. We have studied a large kindred with hereditary persistence of fetal haemoglobin (HPFH). Using a genetic mapping strategy and statistical methods that account simultaneously for the effects of several genetic factors, we have demonstrated that in addition to the two factors (beta thalassaemia and Xmn I-G gamma site) on chromosome 11p, there is a third major genetic determinant for fetal Hb production localized on chromosome 6q.

Diabetic retinopathy is not associated with carbonic anhydrase gene polymorphisms.

PURPOSE: Carbonic anhydrase is elevated in the vitreous of patients with proliferative diabetic retinopathy (PDR). This study aimed to determine if common polymorphisms in the carbonic anhydrase (CA) gene influence susceptibility to diabetic retinopathy (DR). METHODS: In this multicentered study, a total of 235 control subjects with no DR, 158 subjects with nonproliferative DR (NPDR), 132 with proliferative DR (PDR), and 93 with clinically significant macular edema (CSME) were recruited. Blinding DR was defined as severe NPDR, PDR or CSME. DR subjects were drawn from both type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) populations. Ten tag single nucleotide polymorphisms were selected to cover the majority of genetic diversity across the CA gene. RESULTS: After adjustments were made for sex, disease duration, and HbA(1)c, no associations were found between any CA polymorphisms or haplotypes with any type of retinopathy in T1DM or T2DM. CONCLUSIONS: Sequence variation in CA is not associated with the risk of developing retinopathy in T1DM or T2DM and increases the likelihood that elevated vitreous CA may be a consequence rather than cause of DR. Further genetic studies are required to have a better understanding of the pathogenesis of this debilitating diabetic complication.

The role of the Met98Lys optineurin variant in inherited optic nerve diseases.

AIMS: To investigate the role of the common OPTN Met98Lys variant as a risk allele in open-angle glaucoma (OAG), autosomal dominant optic atrophy (ADOA) and Leber's hereditary optic neuropathy (LHON). METHODS: The presence of the Met98Lys variant was determined in a total of 498 (128 with normal-tension glaucoma (NTG)) patients with OAG, 29 patients who had myocilin-related OAG, 101 patients from ADOA pedigrees, 157 patients from LHON pedigrees and 218 examined OAG age-matched normal controls. RESULTS: 17 of 218 (7.8%) controls had the Met98Lys variant. 28 (5.6%) patients with OAG were Met98Lys positive. More Met98Lys carriers were found in the NTG group than in the high-tension glaucoma (HTG) group (p = 0.033). However, no significant difference was observed between the NTG and control cohorts (p = 0.609). Two MYOC mutation carriers were found to have the variant. The variant was found in 1 of 10 pedigrees with ADOA and in 8 of 35 pedigrees with LHON. CONCLUSION: Data from this study do not support a strong role for the OPTN Met98Lys variant in glaucoma, ADOA or LHON. However, a weak association was observed of the variant with NTG compared with that with HTG. Meta-analysis of all published data on the variant and glaucoma confirmed that the association, although weak, is highly statistically significant in the cohort with glaucoma versus controls.

Nail-patella syndrome and its association with glaucoma: a review of eight families.

BACKGROUND: Nail-patella syndrome (NPS) is a rare autosomal dominant syndrome, characterised by dysplasia of the nails, patellae, elbows and iliac horns. Mutations in the LMX1B gene were found in four North American families in whom glaucoma cosegregated with NPS. AIMS: To investigate the association of glaucoma with NPS in Australian families and to determine how common NPS is in Australia. METHODS: One family with NPS and glaucoma was identified from the Glaucoma Inheritance Study in Tasmania. A further 18 index cases of NPS were identified from the genetics database for southeastern Australia. Eight of these pedigrees were available for comprehensive glaucoma examination on available family members. DNA was sequenced for mutations in LMX1B. RESULTS: In total, 52 living cases of NPS were identified suggesting a minimum prevalence of at least 1 in 100 000. 32 subjects from eight NPS pedigrees (four familial and four sporadic cases) were examined. 14 subjects had NPS alone. 4 subjects had NPS and glaucoma or ocular hypertension. Five pedigrees with NPS had a reported family history of glaucoma, although some of these people with glaucoma did not have NPS. LMX1B mutations were identified in 5 of the 8 index cases-three sporadic and two familial. Two of the six (33%) participants over 40 years of age had developed glaucoma, showing increased risk of glaucoma in NPS. CONCLUSION: Patients with NPS should be examined regularly for glaucoma. However, because the families with NPS are ascertained primarily from young probands or probands who are isolated cases, the exact level of risk is unclear.

Lack of association of p53 polymorphisms and haplotypes in high and normal tension open angle glaucoma.

BACKGROUND: The final common pathway for open angle glaucoma (OAG) is retinal ganglion cell apoptosis. Polymorphisms in p53, a major regulator of apoptosis, affect the efficiency of cell death induction. Association studies of p53 haplotypes and OAG have had conflicting results. OBJECTIVE: To examine the association between p53 haplotypes and OAG in a larger white population than in previous reports, and extend the analysis to normal tension glaucoma. METHODS: 345 unrelated people with OAG were recruited (283 subjects with high tension glaucoma and 62 with normal tension glaucoma) and compared with 178 age matched controls. Genomic DNA was analysed for the p53 codon 72 Arg/Pro polymorphism as well as for the presence or absence of a 16 bp intron 3 insertion. RESULTS: In this white cohort no association was found between glaucoma (high or normal tension) and either sequence variant or haplotype. CONCLUSIONS: The p53 codon 72 Arg/Pro polymorphism is not associated with age of onset or severity of glaucoma.

The telomere of human chromosome 1p contains at least two independent autosomal dominant congenital cataract genes.

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.

Fetal hemoglobin levels in adults.

The synthesis of fetal hemoglobin (HbF) is normally reduced to very low levels of less than 0.6% of the total hemoglobin in adults. The HbF is restricted to a sub-population of erythrocytes termed 'F-cells'; 85% of the normal adult population have 0.3% to 4.4% F-cells. The levels of HbF and F-cells vary by more than 10-fold in normal adults; family studies show that these levels are genetically controlled but the number and nature of these genetic factors are still poorly understood. HbF levels may be increased in adults in a number of inherited and acquired disorders, accompanied by an increase in both the number of F-cells and the amount of HbF per F-cell. The clinical significance of these conditions with raised HbF relates to their interaction in disorders such as sickle cell disease and beta thalassaemia in which raised levels of HbF can lead to considerable amelioration of disease severity. Study of the 'natural' mutants primarily associated with increased HbF has provided considerable insight into the understanding of the control of globin gene regulation and hemoglobin switching. Currently considerable effort is being channelled into clinical trials and the search for the 'ideal' therapeutic agents which could increase HbF in adult life with minimal drug toxicity.

Evaluation of the myocilin (MYOC) glaucoma gene in monkey and human steroid-induced ocular hypertension.

PURPOSE: Glucocorticoid-induced ocular hypertension (the steroid response) may result in optic nerve damage that very closely mimics the pathologic course of primary open angle glaucoma (POAG). In addition, patients with glaucoma and their relatives are much more likely to exhibit the steroid response than unaffected individuals, suggesting a potential link between the steroid response and POAG. Recently, the expression of a gene (MYOC) in the trabecular meshwork was shown to be steroid-induced. MYOC variations thought to be disease-causing also were found in 3% to 5% of POAG cases. The purpose of this study was to determine whether some variations in MYOC might be involved in steroid-induced ocular hypertension. METHODS: Seventy human steroid responders and 114 control subjects were screened for variations in the coding sequence and promoter of MYOC. Also, topical doses of dexamethasone (DEX) were administered to cynomolgus monkeys to determine their steroid responsiveness, and the MYOC orthologue was cloned from the cynomolgus monkey. RESULTS: Overall, 109 instances of 20 different sequence variations were identified in the human myocilin gene. However, only four of these (each observed in a single individual) met the study criteria for a possible phenotype-altering variation. Three of these were present in steroid responders and one in a control patient, a distribution that was not statistically significant (P: = 0.3). In addition, the allele frequency of a closely flanking marker was compared between the steroid responders and the control subjects, and no evidence for linkage disequilibrium was observed. Reproducible and reversible ocular hypertension was induced in approximately 40% of the monkeys treated with DEX, similar to that seen in man. Ten monkeys were screened for MYOC mutations with single-strand conformation polymorphism (SSCP) analysis. Overall, 37 instances of 13 different sequence variations were observed. Four of these changes met the study criteria for a possible phenotype-altering variation, and these were equally distributed between responder and nonresponder monkeys. CONCLUSIONS: This study identified no statistically significant evidence for a link between MYOC mutations and steroid-induced ocular hypertension.

Accuracy and implications of a reported family history of glaucoma: experience from the Glaucoma Inheritance Study in Tasmania.

OBJECTIVES: To ascertain the prevalence of previously undiagnosed primary open-angle glaucoma (POAG) within 5 large POAG pedigrees and to evaluate the reliability of a reported family history of glaucoma within these pedigrees. METHODS: The Glaucoma Inheritance Study in Tasmania (GIST) identified several large adult POAG pedigrees. Intraocular pressure (IOP), optic disc stereophotography, and automated perimetry were performed on all adult pedigree members. Participants were classified as normal (IOP <22 mm Hg and normal optic disc and field); glaucoma suspect (normal field, but an IOP >/=22 mm Hg and/or suspicious optic disc); or POAG (field defect and glaucomatous optic disc). Some individuals with POAG had been previously diagnosed by their local ophthalmologist; others were diagnosed as a result of the GIST project. Family members with a prior diagnosis of POAG were asked to report if they were aware of any relatives with POAG. This reported family history was then directly compared with the actual pedigree (before the diagnosis of new cases) to calculate agreement. MAIN OUTCOME MEASURE: The rate of glaucoma in pedigrees and percentage of previously diagnosed glaucoma cases who were aware of the positive family history of POAG. RESULTS: Four hundred forty-two subjects (mean age, 54 years [range, 13-97 years]) from 5 pedigrees were examined: 316 subjects (71%) were normal, 47 (11%) were previously diagnosed with POAG, and 8 (2%) were previously diagnosed glaucoma suspects; 30 cases (7%) of POAG and 41 suspects (9%) were newly diagnosed as a direct result of the GIST examination. Of the 47 previously diagnosed POAG cases, 41 were questioned about their prior knowledge of any family history and 11 (27%) were unaware of their family history of POAG. CONCLUSIONS: Examination of all adult subjects from POAG families yields new cases. Even in large POAG pedigrees, 27% of previously diagnosed POAG patients were unaware of their positive family history. These findings suggest that a higher percentage of adult POAG may be inherited than hitherto reported. Arch Ophthalmol. 2000;118:900-904

Survival of nontypeable Haemophilus influenzae in macrophages.

In this study we have investigated the ability of nonencapsulated, nontypeable Haemophilus influenzae, NT477 to survive in the J774 mouse macrophage-like cell line. Viable, intracellular nontypeable H. influenzae could still be recovered from macrophages 72 h after phagocytosis. In contrast, H. influenzae strain Rd, an avirulent, nonencapsulated variant of a serotype d strain, was killed within 24 h. These differences suggest that NT477, in comparison to Rd, possesses unique attributes that enable it to survive in macrophages for prolonged periods. To determine whether this trait is ubiquitous amongst nontypeable H. influenzae, 33 primary clinical isolates obtained from children with otitis media were screened for their ability to survive in macrophages. Of these isolates, 82% were able to persist in an intracellular environment for periods of at least 24 h. The number of viable organisms recovered at this time ranged from 2x10(4) to 50 colony-forming units per strain indicating that the extent to which nontypeable H. influenzae can resist macrophage-mediated killing varies between strains.

The Taa1 restriction enzyme provides a simple means to identify the Q368STOP mutation of the myocilin gene in primary open angle glaucoma.

PURPOSE: To identify a rapid and reliable method to detect the Glutamine 368 STOP (Q368STOP) disease-predisposing allele of the myocilin gene associated with adult onset, primary, open-angle glaucoma. METHODS: Individuals with the Q368STOP mutation of the myocilin gene were identified from a cohort of primary open-angle glaucoma patients from Tasmania and subjected to Taa1 restriction digestion. RESULTS: In the Tasmanian family presented, screening with the Taa1 restriction enzyme successfully confirmed identification of all individuals with the Q368STOP mutation. CONCLUSIONS: The use of the Taa1 restriction enzyme offers a relatively simple, rapid, and reproducible technique that could be applied to detect the Q368STOP mutation of the myocilin gene.

Laboratory methods in ophthalmic genetics: obtaining DNA from patients.

DNA samples are the fundamental research substrate in genetics. Although methodology and cost-effectiveness in molecular biology have improved dramatically, collecting biological samples and extracting DNA continue to be expensive and time-consuming steps of genetic research. This article reviews the issues surrounding the choice of biological samples for methods of DNA extraction as well as the storage and transport of biological and DNA samples for genetic studies.

Retinopathy of prematurity: recent advances in our understanding.

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Aetiology of congenital and paediatric cataract in an Australian population.

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.

Investigation of crystallin genes in familial cataract, and report of two disease associated mutations.

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.

Retinopathy of prematurity: recent advances in our understanding.

Retinopathy of prematurity (ROP) has been recognised as an important cause of childhood visual impairment and blindness since the 1940s when improved facilities and treatment increased the survival rate of premature infants. Although its incidence and severity have been decreasing in developed countries over the past two decades, both are increasing in developing nations. ROP is consequently targeted as an important but avoidable disease. This review provides an updated summary and discussion of much of the work that has been produced through population, animal, cell culture, and genetic research. The authors examine the prevalence, risk factors, and possible causes of the disease with a particular focus on genetic studies. They conclude that while significant reductions in the disease have occurred in developed countries, further research is required to fully understand and prevent the disease. In the meantime, development and implementation of appropriate screening and treatment strategies will be critical in reducing blindness in developing countries.

Genetic factors in athetoid cerebral palsy.

Within the cerebral palsy syndromes, athetosis is most commonly causally associated with serious perinatal complications. Genetic factors are thought to play a lesser role, although the risk of recurrence in siblings has been suggested to be as high as 10%. We have conducted a clinical study of 22 subjects with a diagnosis of athetoid cerebral palsy and a review of the literature aiming to identify instances of familial recurrence of athetoid cerebral palsy. The birth history, family history, and previous investigations of subjects with athetoid cerebral palsy were studied and subjects were clinically examined for evidence of an underlying genetic etiology. Factors suggesting a genetic cause were specifically sought, such as advanced paternal age, progression of symptoms, and associated congenital abnormalities. No subjects in the study group had similarly affected relatives, and additional features suggesting a genetic cause were not observed. A literature search identified 16 instances of familial recurrence of athetoid cerebral palsy. Familial cases were typically associated with significant spasticity, microcephaly, intellectual disability, seizures, and a lack of history of birth asphyxia, and most could be explained by either autosomal-recessive or X-linked-recessive inheritance. The genetic contribution to athetoid cerebral palsy is small, with an overall risk of recurrence in siblings of about 1%. This risk is lower than previously suggested in the literature.

Situs inversus totalis and congenital hypoglossia.

Hypoglossia is a rare congenital malformation, occurring either as an isolated malformation or in association with other deformities, particularly limb defects. We describe a female infant with congenital hypoglossia, micrognathia and situs inversus. The main complications were airway compromise and feeding difficulties requiring tracheostomy and gastrostomy. Situs inversus and hypoglossia have been reported together on six previous occasions, with all cases being sporadic. Situs inversus-hypoglossia falls into a spectrum of aetiologically non-specific developmental field defects that includes the Aglossia-adactylia spectrum and the Agnathia-holoprosencephaly spectrum. Situs inversus-hypoglossia may represent a mild form of Agnathia-holoprosencephaly.