Biomedical subjects

Alan Shiels

Publications and source records attributed to Alan Shiels.

4 recordsLinked to original sources

PubMed2003

Galactokinase gene mutations and age-related cataract. Lack of association in an Italian population.

PURPOSE: To investigate possible associations between sequence changes in the galactokinase gene (GALK1) and age-related cataract in a European population. METHODS: Persons without lens opacities and persons with clinically significant age-related cataract were selected from those participating in the Collaborative Italian-American Clinical Trial of Nutritional Supplements and Age-Related Cataract or from those attending the Section of Ophthalmology of the University of Parma for cataract surgery. Type and severity of the opacities were assessed by slit-lamp and retro-illumination lens photographs. Mutations in GALK1 were identified by PCR amplification of individual exons and flanking sequences and sequencing using fluorescent terminator technology in an ABI 377 Prism or 3100 automated DNA sequencer. RESULTS: DNA samples were obtained from 115 individuals with clear lenses and from 185 individuals with cataract (106 with any nuclear, 88 with any cortical, and 25 with any posterior sub capsular cataract). 157 of the 185 patients with cataract (85%) were age-matched with a control within an age range of plus or minus 1 year. SNPs causing amino acid changes in the galactokinase protein were identified in exon 4; I184M, 1/115 control versus 0/185 cataractous individuals, p=0.38, exon 6; G274D, 0/115 control versus 1/185 cataractous individuals, p>0.99, and exon 7; V338A, 0/115 control versus 1/185 cataractous individuals, p>0.99. Thus, there were no significant differences in the distribution of sequence alterations resulting in amino acid changes between control and cataractous individuals. Eighty samples showed a C to T transition 43 bases into intron 7 (46 cataracts and 34 controls). Testing the distribution of the intron 7 findings showed Hardy-Weinberg equilibrium for both cases (p=0.73) and controls (p=0.51). There was no difference in C/T distribution between cases and controls (p=0.27). CONCLUSIONS: In this northern Italian population age-related cataract does not appear to be associated with GALK1 alleles. Since this is due to a lack of sequence changes in both affected and control individuals, this study cannot rule out the possibility of an association in other populations.

Aged↗

PubMed2003

Lens structure in MIP-deficient mice.

In this study we used correlative light, scanning, and transmission (freeze-etch) electron microscopy to characterize lens structure in normal mice and compare it with that in mice deficient in the major intrinsic protein (MIP) of fiber cells. Grossly, wild-type lenses were transparent and had typical Y sutures at all of the ages examined. These lenses had fibers of uniform shape (hexagonal in cross section) arranged in ordered concentric growth shells and radial cell columns. In addition, these fibers had normal opposite end curvature and lateral interdigitations regularly arrayed along their length. Ultrastructural evaluation of these fibers revealed anterior and posterior end segments characterized by square array membrane on low-amplitude wavy fiber membrane. Approximately 13% of the equatorial or mid segments of these same fibers were specialized as gap junctions (GJs). In contrast, heterozygote lenses, while initially transparent at birth, were translucent by 3 weeks of age, except for a peripheral transparent region that contained fibers in the early stages of elongation. This degradation in clarity was correlated with abnormal fiber structure. Specifically, although the mid segment of these fibers was essentially normal, their end segments lacked normal opposite end curvature, were larger than normal, and had a distinct non-hexagonal shape. As a result, these fibers failed to form typical Y sutures. Furthermore, the nuclear fibers of heterozygote lenses were even larger and lacked any semblance of an ordered packing arrangement. Grossly, homozygote lenses were opaque at all ages examined, except for a peripheral transparent region that contained fibers in the early stages of elongation. All fibers from homozygote lenses lacked opposite end curvature, and thus failed to form any sutures. Also, these fibers were essentially devoid of interlocking devices, and only 7% of their mid segment was specialized as GJs. The results of this study suggest that MIP has essential roles in the establishment and maintenance of uniform fiber structure, and the organization of fibers, and as such is essential for lens function.

Animals↗

PubMed2003

Cell death triggered by a novel mutation in the alphaA-crystallin gene underlies autosomal dominant cataract linked to chromosome 21q.

Hereditary cataract is a clinically and genetically heterogeneous lens disease that accounts for a significant proportion of visual impairment and blindness in childhood. The alphaA-crystallin (CRYAA) gene (CRYAA) encodes a member of the small-heat-shock protein (sHSP) family of molecular chaperones and is primarily and abundantly expressed in the ocular lens. Here, we have used linkage analysis to identify a novel missense mutation in CRYAA that underlies an autosomal dominant form of 'nuclear' cataract segregating in a four-generation Caucasian family. A maximum two-point LOD score (Z(max)) of 2.19 (maximum recombination fraction, theta(max)=0) and multipoint Z(max) of 3.3 (theta(max)=0) was obtained at marker D21S1885. Haplotype analysis indicated that the disease gene lay in the approximately 2.7 Mb physical interval between D21S1912 and D21S1260 flanking CRYAA on 21q22.3. Sequence analysis identified a C --> T transition in exon 1 of CRYAA from affected individuals that was predicted to result in the nonconservative substitution of cysteine for arginine at codon 49 (R49C). Transfection studies of lens epithelial cells revealed that, unlike wild-type CRYAA, the R49C mutant protein was abnormally localized to the nucleus and failed to protect from staurosporine-induced apoptotic cell death. This study has identified the first dominant cataract mutation in CRYAA located outside the phylogenetically conserved 'alpha-crystallin core domain' of the sHSP family.

Alleles↗

PubMed2002

A nonsense mutation in CRYBB1 associated with autosomal dominant cataract linked to human chromosome 22q.

Autosomal dominant cataract is a clinically and genetically heterogeneous lens disorder that usually presents as a sight-threatening trait in childhood. Here we have mapped dominant pulverulent cataract to the beta-crystallin gene cluster on chromosome 22q11.2. Suggestive evidence of linkage was detected at markers D22S1167 (LOD score [Z] 2.09 at recombination fraction [theta] 0) and D22S1154 (Z=1.39 at theta=0), which closely flank the genes for betaB1-crystallin (CRYBB1) and betaA4-crystallin (CRYBA4). Sequencing failed to detect any nucleotide changes in CRYBA4; however, a G-->T transversion in exon 6 of CRYBB1 was found to cosegregate with cataract in the family. This single-nucleotide change was predicted to introduce a translation stop codon at glycine 220 (G220X). Expression of recombinant human betaB1-crystallin in bacteria showed that the truncated G220X mutant was significantly less soluble than wild type. This study has identified the first CRYBB1 mutation associated with autosomal dominant cataract in humans.

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