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PubMed2005

P gene mutations associated with oculocutaneous albinism type II (OCA2).

Oculocutaneous albinism type II (OCA2) is the most common form of albinism in humans. OCA2 has been previously associated with mutations of the P gene, the human homologue to the murine pink-eyed dilution gene. The P gene encodes a 110 kDa protein containing 12 potential membrane spanning domains and is associated with melanosomal membranes. The specific function of the P protein is currently unknown but is thought to be involved in tyrosinase processing and transport. We report nine novel mutations in the P gene associated with OCA2. These include two missense mutations, c.1938A>C (p.Ile646Val) and c.1556T>C (p.Val519Ala); one nonsense mutation c.612G>A (p.Trp204X); five frameshift mutations: c.2372_2373delTC, c.1555delG, c.1938_1939insC, c.2050delT, and c.1045_1046delAT; and a splice site mutation c.1951+1G>A. We also report 12 novel polymorphisms including one amino acid substitution, c.2365_2366GC>CA (p.Ala789Glu). At present, there is no functional assay to determine if a mutation is truly pathogenic. The presence of numerous polymorphisms of the P gene in the coding region, several of which result in amino acid substitutions, makes molecular diagnosis problematic. To ensure accurate molecular diagnosis, further mutational analysis will be necessary to produce a comprehensive list of mutations associated with OCA2. This information will also help define the critical functional domains of the P protein. Mutations associated with OCA2 can be found in the Albinism Database (http://albinismdb.med.umn.edu).

Albinism, Oculocutaneous↗

PubMed1995

Risk of cutaneous melanoma associated with pigmentation characteristics and freckling: systematic overview of 10 case-control studies. The International Melanoma Analysis Group (IMAGE).

Using individual subject data from 10 case-control studies, comprising over 3000 cases and almost 4000 controls, we have estimated the relative risk of melanoma associated with aspects of complexion, namely, hair, eye and skin colour and freckling in adulthood, and have examined the relationships between these factors and naevus count in terms of melanoma risk. Compared with individuals with black or dark brown hair, the relative risks for developing melanoma in those with light brown, blonde and red hair were 1.49 (95% CI 1.31, 1.70), 1.84 (95% CI 1.54, 2.21) and 2.38 (95% CI 1.90, 2.97), respectively. Individuals with blue eyes had a risk 1.55 (95% CI 1.35, 1.78) times that for those with brown eyes, or 1.15 (95% CI 0.94, 1.40) after adjusting for hair colour and freckling in adulthood. The relative risks associated with hair and eye colour were independent of those for naevus count and skin colour. Light skin colour and high freckle density were also highly significant risk factors, independent of each other and of naevus count and hair and eye colour. The risks associated with these factors, while individually modest, are largely independent, and thus pigmentation characteristics and freckling tendency should be useful in identifying high risk groups to be targeted for prevention.

Case-Control Studies↗

PubMed1989

The claret locus in Drosophila encodes products required for eyecolor and for meiotic chromosome segregation.

The claret (ca) locus in Drosophila encodes products that are needed both for wild-type eyecolor and for correct meiotic chromosome segregation. Mutants described previously provide evidence that two mutationally independent coding regions are present at ca. We have recovered six new P element-induced and one spontaneous ca mutant. Four of these new mutants affect both eyecolor and chromosome segregation. The high frequency of co-mutation of these two functions suggests that the corresponding genes are closely adjacent to one another. We recovered genomic DNA sequences corresponding to the ca locus by chromosome walking, and showed using revertant analysis that the cloned region encodes ca+. Transformation experiments demonstrate that the mutant effect resulting in meiotic chromosome non-disjunction (nd) and loss is fully rescued by DNA from the cloned region. Two RNAs of 7.4 and 2.2 kb have been identified by Northern blot analysis as the putative eyecolor and segregational products. Expression of the RNAs with respect to males and females, and their presence or absence in ca and nd mutants indicate that the 7.4 kb RNA corresponds to the product needed for wild-type eyecolor and the 2.2 kb RNA is the product required for normal chromosome segregation. These RNAs are transcribed in opposite directions to one another. Alleles that affect both eyecolor and chromosome segregation are deletion mutants that affect both transcripts. Thus, the putative eyecolor and segregational products are encoded by separate genes. Mutants that affect both eyecolor and chromosome segregation apparently do so because they delete essential regions of both genes.

Alleles↗

PubMed1975

Real-time color B-scan ultrasonography.

The development and early clinical results of a real-time color B-scan ultrasonoscope are described. This instrument uses color to display detailed echo amplitude information more quantitatively than is possible with gray scale. With real time, dynamic changes are seen during the examination. Conversion of the amplitude information into binary coded decimal code permits separation into ten color steps and also eliminates "blooming" of the cathode ray tube, as seen in black and white. Integrated circuitry is used, providing a portable, relatively inexpensive unit. Early clinical work in ophthalmology is illustrated.

Color↗

PubMed1983

Esterase activities in adult rabbit eyes.

The rational design of prodrugs to improve the therapeutic efficacy of existing drugs would be expedited if the nature of the in vivo enzymatic conditions that regenerate the drugs from their prodrugs is known. Using albino and pigmented rabbits as models, this research seeks to delineate the esterase activities in their corneas, irises, ciliary bodies, and aqueous humor, which are intimately involved in the disposition of drugs from topical dosing. This was achieved by monitoring the hydrolysis kinetics of alpha-naphthyl acetate, both in the presence and absence of esterase inhibitors, upon incubation with aqueous humor and homogenates of cornea, iris, and ciliary body. It was found that in both breeds of rabbits, esterase activity was the highest in the iris-ciliary body followed by the cornea and then the aqueous humor, and that multiple esterases probably existed in the aqueous humor, and the ocular tissues studied. However, the esterase activity in the cornea and iris-ciliary body of the pigmented rabbit was greater when compared with the albino rabbit. Based on these results, drugs and prodrugs containing ester linkages can undergo varying extents of esterase-mediated hydrolysis while permeating the cornea and upon entering the aqueous humor, iris, and ciliary body. Moreover, in view of the differences in esterase activity that exist between the albino and pigmented rabbits, it would be necessary to employ both breeds of rabbits in evaluating the rate and extent to which ocular ester prodrugs would be converted to their parent compounds.

Animals↗

PubMed1983

Heterochromia iridis and Horner's syndrome due to paravertebral neurilemmoma.

A case of heterochromia iridis and Horner's syndrome is reported in a 7-year old girl with paravertebral neurilemmoma. These clinical findings can be useful in the early diagnosis of mediastinal tumors in the paravertebral axis. While typically associated with neuroblastoma, these findings can be due to tumors which are inately benign--in this case neurilemmoma. The mechanism for heterochromia is briefly discussed.

Child↗

PubMed1993

Pluripotency of cultured rabbit inner cell mass cells detected by isozyme analysis and eye pigmentation of fetuses following injection into blastocysts or morulae.

Pluripotency of isolated rabbit inner cell masses (ICMs) and cultured (3 days) inner cell mass (ICM) cells was tested by injecting these donor cells into day 3.5 blastocysts (experiment 1) or day 3 morulae (experiment 2) to produce chimeric embryos. Injected (n = 107) and noninjected (n = 103) embryos were transferred to the opposite uterine horns of the same recipient females. Chimerism was determined by adenosine deaminase (ADA) isozyme analysis on fetal tissue and by eye pigmentation at midgestation. In experiment 1, 53% and 64%, respectively, of blastocysts injected with ICMs or cultured ICM cells developed to midgestation, compared with 52% and 48% for controls. Of these fetuses, four (31%) and one (6%), respectively, had ADA chimerism. In experiment 2, 38% and 62%, respectively, of the morulae injected with ICMs or cultured ICM cells developed to midgestation, compared with 46% and 56% for control morulae. Six (43%) chimeric fetuses from morulae injected with ICMs were detected by ADA analysis, but 12 (86%) chimeric fetuses were detected by eye pigmentation, indicating that eye pigmentation was a more sensitive marker for chimerism than our ADA assay. None of the 14 fetuses recovered after injecting morulae with cultured ICM cells were chimeric with either marker. No chimeras developed from control embryos. These studies demonstrate 1) that pregnancy rates are not compromised by injection of blastocysts or morulae with ICMs or cultured ICM cells, 2) that chimeric rabbit fetuses can be produced by injecting ICMs into either blastocysts or morulae, and 3) that cultured ICM cells can contribute to embryonic development when injected into blastocysts.

Animals↗

PubMed1993

Catecholamines in Drosophila melanogaster (wild type and ebony mutant) decuticalarized retinas and brains.

The concentrations of catecholamines were determined in the decuticalarized retinas and brains at different ages in wildtype and ebony Drosophila melanogaster using the HPLC-technique with an electrochemical detector. L-Dopa, dopamine (DA), alpha-methyldopa (alpha-MD) and unidentified compounds X1, X2 and X3 were found in decuticalarized retinas and brains of wildtype and ebony at different ages. Retinas and brains of the mutant ebony have higher concentrations of L-Dopa, DA and alpha-MD than the wildtype. In both wildtype and ebony, the concentrations of X1, X2 and X3 were found to be higher in decuticalarized retinas than in brains. The identity and importance of X1, X2 and X3 are still unknown.

Amino Acid Metabolism, Inborn Errors↗

PubMed1993

Postnatal ocular expression of tyrosinase and related proteins: disruption by the pink-eyed unstable (p(un)) mutation.

Ocular pigmentation in the mouse occurs primarily postnatally as a result of the melanization of neural crest-derived melanocytes. Using immunologic and biochemical techniques, we demonstrate that in normal mice the expression of tyrosinase and the related proteins TRP-1 and TRP-2, rises during the first week of life, remains elevated for a week, and then steadily declines to low levels by adulthood. Sucrose gradient density centrifugation demonstrates that tyrosinase, TRP-1 and TRP-2 are present in high molecular weight forms in the eyes of wild-type mice. The normal time course is disrupted in mice carrying the pink-eyed unstable (p(un)) mutation at the P-locus, a model for tyrosinase-positive albinism in man. Tyrosinase and TRP-2 are present at wild-type levels in the eyes of p(un)/p(un) mice at birth, but, rather than rising, their levels rapidly decline over the first week of life. TRP-1 is almost undetectable, even at birth. High molecular weight complexes could not be detected in eyes of p(un)/p(un) mice. Our results suggest that postnatal ocular melanogenesis in the mouse presents an attractive model for the study of the orderly expression and action of the proteins involved in eumelanin synthesis, and that the p(un) mutation disrupts this temporally controlled process.

Albinism↗

PubMed1999

Increased pigmentation of iridial melanocytes in primates induced by a prostaglandin analogue.

The melanocytes in the mammalian eye have been thought to produce melanin only during fetal development and in the very young individual. The recent discovery that latanoprost, a prostaglandin analogue used in the treatment of glaucoma, causes increased pigmentation of the iris in monkeys and in humans indicates that the iridial melanocytes can produce melanin in adult individuals. Using microautoradiography of HG-(3)H-methimazole, a false melanin precursor, we observed in an earlier study that there seems to be an ongoing melanogenesis in adult mice in the iridial melanocytes and in the iridial pigment epithelium. In the present study latanoprost (13,14-dihydro-17-phenyl-18,19,20-trinor-PGF(2alpha)-isoprop yl ester) was applied once daily to the right eye of seven cynomolgus monkeys; the left eye served as an untreated control. Two animals developed clear-cut increased pigmentation of the iris in the treated eye during the first three months of treatment. These animals were injected intravenously with G-(3)H-methimazole and were killed 24 hr after the injection. The eyes were removed, fixed in 4% formalin supplemented with 10% acetic acid and embedded in paraffin or Polybed 812. Sections from the eyes were used for microautoradiography and light microscopic examination. A high uptake of radioactivity was observed in a few melanocytes in the iris of the untreated eye. There were also a low uptake in the melanocytes in the stroma of the ciliary body and the choroid. No accumulation was observed in the iridial or retinal pigment epithelium. In the iris of the treated eye the only observed difference from the untreated eye was an increased amount of melanin in the iridial melanocytes and an increased uptake of radioactivity in a great number of these cells. Thus it seems likely that treatment with latanoprost in some individuals causes an increase of the low normal melanin synthesis in iridal melanocytes.

Animals↗

PubMed1996

Effects of 3-iodo-L-tyrosine, a tyrosine hydroxylase inhibitor, on eye pigmentation and biogenic amines in the planarian, Dugesia dorotocephala.

Planarians (Dugesia dorotocephala) were evaluated as bioassay organisms to detect inhibition of tyrosine hydroxylase, the rate-limiting enzyme in the synthesis of catecholamines. Thirty planaria per dose were exposed to 0 (control), 0.001, 0.01, 0.1, or 1 mM 3-iodo-L-tyrosine (monoiodotyrosine or MIT) in standard test media beginning 24 hr before decapitation and continuing for 13 days. Complete regeneration of normal heads occurred over the first 6 days in all dose groups, a response reported to be partially dependent on catecholamines. Beginning on Day 7, the black eye pigments began fading in the 0.1 and 1 mM dose groups and were completely absent macroscopically and histologically by Day 11. The 0, 0.001, and 0.01 mM dose groups did not lose visible eye pigments. On Day 13, 3 planaria/dose were harvested for histopathology; 15 planaria/dose were decapitated a second time and remained in MIT solutions; and 12 planaria/dose were left intact, placed in fresh control media, and evaluated for eye repigmentation. Normal head regeneration (including eyes) was detected grossly in all groups, even in those animals devoid of eye pigments at the time of decapitation. As before, eye pigments began fading 7 days after decapitation (Day 20 of experiment) and were completely absent in 73 and 33% of the animals in the 0.1 and 1 mM groups, respectively, on Day 25. All animals moved to control media reformed eye pigments, beginning within 48 hr. Analysis of the decapitated heads by HPLC-ECD on Day 13 revealed a significant decrease in dopamine and 5-hydroxytryptamine (serotonin) concentrations in MIT-exposed animals. Tyrosine hydroxylase activity (and possibly tyrosinase activity) was shown to be inhibited by the highest two concentrations for whole planaria homogenates in vitro.

Animals↗

PubMed1997

Comparative effects of intraocular pressure between systemic and topical carbonic anhydrase inhibitors: a clinical masked, cross-over study.

The aims of the following study were to compare the efficacy of Dorzolamide 1% eye drops with systemic Acetazolamide on the ocular pressure diurnal curve in patients with maximal medical therapy. Three ocular pressure curve were performed in glaucomatous patients, already receiving maximal medical therapy. After a baseline curve, patients were pretreated either with Dorzolamide 1% eye drops or 250 mg Acetazolamide tablets in a double-blind cross-over study. Dorzolamide 1% eye drops and 250 mg Acetazolamide tablets significantly reduced intraocular pressure (IOP) at 2 and 4 h after pretreatment. Both treatments caused a significantly additional decrease of IOP despite maximal medical therapy. Dorzolamide 1% eye drops is as effective as Acetazolamide tablets in reducing the IOP curve. Topical carbonic anhydrase inhibitors may represent an additional and safer treatment for those patients with uncontrolled medical glaucoma.

Acetazolamide↗

PubMed1978