A locus for autosomal dominant anterior polar cataract on chromosome 17p

Inherited cataract is a clinically and genetically heterogeneous disease. Here we report the identification of a new locus for an autosomal dominant anterior polar cataract on the short arm of chromosome 17. To map this new locus we performed genetic linkage analysis with microsatellite markers in a four-generation pedigree. After exclusion of seven candidate loci for cataract, we obtained significant positive LOD scores for markers D17S849 (Z = 4.01 / theta = 0.05) and D17S796 (Z = 4.17 / theta = 0.05). Multipoint analysis gave a maximum LOD score of 5.2 (theta max = 0.06) between these two markers. From haplotype analysis, the cataract locus lies in the 13 cM interval between markers D17S849 and D17S796. This study provides the first genetic mapping of an autosomal dominant anterior polar cataract.      

HIV-1 clade C envelopes obtained from late stage symptomatic Indian patients varied in their ability towards relative CD4 usages and sensitivity to CCR5 antagonist TAK-779

The mechanism by which strictly CCR5 using HIV-1 clade C variants exacerbate disease progression in absence of coreceptor switch is not clearly known. We previously reported HIV-1 clade C envelopes (Env) obtained from late stage Indian patients with expanded coreceptor tropism. Here we compared such Envs (having expanded coreceptor tropism) with strictly CCR5 using Envs also obtained from late stage in their capacity to utilize CD4 and CCR5 for productive entry. We found that while envelopes with low CD4 dependence tend to infect primary CD4(+) T cells better than those required optimum CD4 for entry, no significant association was found between low CD4 usage and infectivity of primary CD4(+) T cells by Env-pseudotyped viruses and their sensitivity to CCR5 antagonist TAK-779. Interestingly, Envs that readily infected HeLa cells expressing low CD4 showed relative resistance to T20 indicating that conformational intermediates of these envelopes remained for a shorter period of time than is required for efficient inhibition by T20.     

The prevalence of antiphospholipid antibodies in cases of recurrent pregnancy loss

Antiphospholipid antibodies (aPL) are a diverse family of autoantibodies reactive against negatively charged phospholipid-protein complexes. The clinically significant members include lupus anticoagulant (LA), anticardiolipin antibody (aCL) and reaginic antibodies causing biological false positive (BFP) venereal disease laboratory test (VDRL). Although detected in various clinical scenarios, unexplained fetal loss in women of reproductive age group is the commonest association. Fifty pregnant women of first and second trimester with a history of two or more unexplained pregnancy losses were studied for the presence of LA, aCL and reaginic antibodies. Thirty pregnant women of the same trimester without any history of fetal loss were taken as control. LA was detected in nine (18%) cases and aCL in 12 (24%) cases of the study group. The control group was negative for any autoantibody. The prevalence of aPL in the study group found to be statistically significant. Detection of aPL must be considered in women with previous pregnancies complicated by unexplained fetal wastage.     

Mutations in the RP1 gene causing autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration that affects approximately 1 in 3500 people worldwide. Recently we identified the gene responsible for the RP1 form of autosomal dominant retinitis pigmentosa (adRP) at 8q11-12 and found two different nonsense mutations in three families previously mapped to 8q. The RP1 gene is an unusually large protein, 2156 amino acids in length, but is comprised of four exons only. To determine the frequency and range of mutations in RP1 we screened probands from 56 large adRP families for mutations in the entire gene. After preliminary results indicated that mutations seem to cluster in a 442 nucleotide segment of exon 4, an additional 194 probands with adRP and 409 probands with other degenerative retinal diseases were tested for mutations in this region alone. We identified eight different disease-causing mutations in 17 of the 250 adRP probands tested. All of these mutations are either nonsense or frameshift mutations and lead to a severely truncated protein. Two of the eight different mutations, Arg677X and a 5 bp deletion of nucleotides 2280-2284, were reported previously, while the remaining six mutations are novel. We also identified two rare missense changes in two other families, one new polymorphic amino acid substitution, one silent substitution and a rare variant in the 5'-untranslated region that is not associated with disease. Based on this study, mutations in RP1 appear to cause at least 7% (17/250) of adRP. The 5 bp deletion of nucleotides 2280-2284 and the Arg677X nonsense mutation account for 59% (10/17) of these mutations. Further studies will determine whether missense changes in the RP1 gene are associated with disease, whether mutations in other regions of RP1 can cause forms of retinal disease other than adRP and whether the background variation in either the mutated or wild-type RP1 allele plays a role in the disease phenotype.     

Genetic analysis of the guanylate cyclase activator 1B (GUCA1B) gene in patients with autosomal dominant retinal dystrophies

The guanylate cyclase activator proteins (GCAP1 and GCAP2) are calcium binding proteins which by activating Ret-GC1 play a key role in the recovery phase of phototransduction. Recently a mutation in the GUCA1A gene (coding for GCAP1) mapping to the 6p21.1 region was described as causing cone dystrophy in a British family. In addition mutations in Ret-GC1 have been shown to cause Leber congenital amaurosis and cone-rod dystrophy. To determine whether GCAP2 is involved in dominant retinal degenerative diseases, the GCAP2 gene was screened in 400 unrelated subjects with autosomal dominant central and peripheral retinal dystrophies. A number of changes involving the intronic as well as the coding sequence were observed. In exon 1 a T to C nucleotide change was observed leaving the tyrosine residue 57 unchanged. In exon 3 a 1 bp intronic insertion, a single nucleotide substitution G to A in the intron 3' of this exon, and a GAG to GAT change at codon 155 were observed. This latter change results in a conservative change of glutamic acid to aspartic acid. In exon 4 a 7 bp intronic insertion, a single nucleotide A to G substitution in the intron 5' of this exon, and a single base pair change C to G in the intron 3' of exon 4 were seen. None of these changes would be expected to affect correct splicing of this gene. All these changes were observed in controls. The results of this study do not show any evidence so far that GCAP2 is involved in the pathogenesis of autosomal dominant retinal degeneration in this group of patients. All the changes detected were found to be sequence variations or polymorphisms and not disease causing.     

Development and evaluation of a phage typing scheme for Vibrio cholerae O139

The scenario of cholera that existed previously changed in 1992 and 1993 with the emergence of toxigenic Vibrio cholerae O139 in India. The genesis of the new serogroup formed the impetus to search for O139 phages in and around the country. A total of five newly isolated phages lytic to V. cholerae O139 strains were used for the development of this phage typing scheme. These phages differed from each other and also differed from the existing O1 phages in their lytic patterns, morphologies, restriction endonuclease digestion profiles, and immunological criteria. With this scheme, 500 V. cholerae O139 strains were evaluated for their phage types, and almost all strains were found to be typeable. The strains clustered into 10 different phage types, of which type 1 (38.2%) was the dominant type, followed by type 2 (22.4%) and type 3 (18%). Additionally, a comparative study of phage types in 1993 and 1994 versus those from 1996 to 1998 for O139 strains showed a higher percentage of phage type 1 (40.5%), followed by type 3 (18.8%) during the period between 1993 and 1994, whereas phage type 2 (32. 1%) was the next major type during the period from 1996 to 1998. This scheme comprising five newly isolated phages would be another useful tool in the study of the epidemiology of cholera caused by V. cholerae O139.     

Single embryo transfer

The traditional policy of transferring more than one embryo in an attempt to increase success rates is responsible for the high numbers of multiple pregnancies associated with in-vitro fertilisation. Elective single embryo transfer is the most effective way of reducing multiples and the associated risks of maternal and perinatal morbidity. In selected patients, the combination of such a policy with the opportunity to transfer additional frozen thawed embryos in successive cycles can lead to cumulative livebirth rates similar to those following double embryo transfer. Appropriate eligibility criteria, improvement of cryopreservation techniques and funding arrangements are likely to increase the uptake of elective single embryo transfer.     

Screening of hearing impairment in the newborn using the auditory response cradle.

The Auditory Response Cradle (ARC) is a fully automated microprocessor controlled machine that was designed for the hearing screening of full term neonates. In order to evaluate the ARC, 6000 babies were screened at a district maternity hospital over a period of three years. Every infant subsequently entered a three year follow up programme. One hundred and two babies (1.7%) failed the ARC screen (that is, they failed two ARC tests) and 20 of these were found to have some hearing impairment: in 10 it was severe (80-90 dBHL), in seven moderate (45-60 dBHL), and in three it was mild to moderate (less than 45 dBHL). In addition, of the 20 babies who failed a first test and were discharged before a second could be performed, two were confirmed to have a severe hearing loss; 79 infants failing the screen were cleared on further testing, giving the ARC a false positive rate of 1.3%. On following up all 6000 infants for three years, seven children who passed the neonatal screen were subsequently found to have a hearing loss. For two babies the aetiology was unknown but for five the hearing impairment was either due to a hereditary progressive loss or definite postnatal factors. Progressive and acquired hearing losses cannot be detected at a neonatal screen and this emphasises the need for follow up screens at other stages in the child's life. In this long term study the ARC has been found to have a high detection rate for severe hearing loss and confirms the practical possibility of using a behavioural technique for the universal screening of hearing in neonates.