William S. Oetting

MOLECULAR BASIS OF ALBINISM : MUTATIONS AND POLYMORPHISMS OF PIGMENTATION GENES ASSOCIATED WITH ALBINISM

Albinism, caused by a deficiency of melanin pigment in the skin, hair, and eye (oculocutaneous albinism [OCA]), or primarily in the eye (ocular albinism [OA]), results from mutations in genes involved in the biosynthesis of melanin pigment. The lack of melanin pigment in the developing eye leads to fovea hypoplasia and abnormal routing of the optic nerves. These changes are responsible for the nystagmus, strabismus, and reduced visual acuity common to all types of albinism. Mutations in six genes have been reported to be responsible for different types of oculocutaneous and ocular albinism, including the tyrosinase gene (TYR) and OCA1 (MIM# 203100), the OCA2 gene and OCA2 (MIM# 203200), the tyrosinase‐related protein‐1 gene (TYRP1) and OCA3 (MIM# 203290), the HPS gene and Hermansky‐Pudlak syndrome (MIM# 203300), the CHS gene (CHS1), and Chediak‐Higashi syndrome (MIM# 214500), and the X‐linked ocular albinism gene and OA1 (MIM#300500). The function of only two of the gene products is known tyrosinase and tyrosinase‐related protein‐1 both of which are enzymes in the melanin biosynthetic pathway. Continued mutational analysis coupled with function/structure studies should aid our understanding of the function of the remaining genes and their role in albinism. Mutation and polymorphism data on these genes are available from the International Albinism Center Albinism Database web site (http://www.cbc.umn.edu/tad). Hum Mutat 13:99–115, 1999.

Evidence That a Locus for Familial High Myopia Maps to Chromosome 18p

Myopia, or nearsightedness, is the most common human eye disorder. A genomewide screen was conducted to map the gene(s) associated with high, early-onset, autosomal dominant myopia. Eight families that each included two or more individuals with >=-6.00 diopters (D) myopia, in two or more successive generations, were identified. Myopic individuals had no clinical evidence of connective-tissue abnormalities, and the average age at diagnosis of myopia was 6.8 years. The average spherical component refractive error for the affected individuals was -9.48 D. The families contained 82 individuals; of these, DNA was available for 71 (37 affected). Markers flanking or intragenic to the genes for Stickler syndrome types 1 and 2 (chromosomes 12q13.1-q13.3 and 6p21.3, respectively), Marfan syndrome (chromosome 15q21.1), and juvenile glaucoma (chromosome 1q21-q31) were also analyzed. No evidence of linkage was found for markers for the Stickler syndrome types 1 and 2, the Marfan syndrome, or the juvenile glaucoma loci. After a genomewide search, evidence of significant linkage was found on chromosome 18p. The maximum LOD score was 9.59, with marker D18S481, at a recombination fraction of .0010. Haplotype analysis further refined this myopia locus to a 7.6-cM interval between markers D18S59 and D18S1138 on 18p11.31.

Novel Polymorphisms Associated with Tacrolimus Trough Concentrations: Results from a Multicenter Kidney Transplant Consortium

Background. The CYP4503A5*1 genotype is associated with lower tacrolimus concentrations. Although its effect is important, it incompletely explains the variability in tacrolimus concentrations and has a relatively low minor allele frequency in whites relative to African Americans (AA). Methods. We studied clinical and recipient genetic correlates of dose-normalized tacrolimus troughs (n=12,277) in the first 6 months posttransplant using a customized single-nucleotide polymorphism chip with 2722 variants in a large, ethnically diverse (144 AA and 551 non-AA) adult kidney transplant population through a seven-center consortium. Results. During the 6-month study, AAs had consistently lower median (interquartile range) troughs than non-AAs, 6.2 (4.4–8.4) ng/mL vs. 8.3 (6.4–10.4) ng/mL (P<0.0001), despite 60% higher daily doses, 8 (5–10) mg vs. 5 (4–7) mg (P<0.0001). The median tacrolimus trough concentration in week 1 posttransplant was particularly low in AAs (2.1 [1.2–3.5] ng/mL) compared with non-AAs (5.0 [3.1–8.2] ng/mL) (P<0.0001), despite similar initial doses. In single-variant analysis, CYP3A5*3 (rs776746) was the top variant (P=2.4×10−33) associated with troughs. After adjustment for CYP3A5*3, clinical factors and race, 35 additional variants were identified (P<0.01, not significant at false discovery rate 20%). In the final multivariant, regression models beginning with these variants and clinical factors, seven variants were identified in the non-AA and seven variants in the AA group towards the first trough concentrations. Rs776746 (CYP3A5), rs2239393 (COMT) and diabetes were the only factors common in both populations. Conclusion. We identified variants beyond CYP3A5*3, which may further explain pharmacokinetic variability of tacrolimus and demonstrated that important variants differ by race.

Dosing equation for tacrolimus using genetic variants and clinical factors

AIM To develop a dosing equation for tacrolimus, using genetic and clinical factors from a large cohort of kidney transplant recipients. Clinical factors and six genetic variants were screened for importance towards tacrolimus clearance (CL/F). METHODS Clinical data, tacrolimus troughs and corresponding doses were collected from 681 kidney transplant recipients in a multicentre observational study in the USA and Canada for the first 6 months post transplant. The patients were genotyped for 2,724 single nucleotide polymorphisms using a customized Affymetrix SNP chip. Clinical factors and the most important SNPs (rs776746, rs12114000, rs3734354, rs4926, rs3135506 and rs2608555) were analysed for their influence on tacrolimus CL/F. RESULTS The CYP3A5*1 genotype, days post transplant, age, transplant at a steroid sparing centre and calcium channel blocker (CCB) use significantly influenced tacrolimus CL/F. The final model describing CL/F (l h(-1)) was: 38.4 ×[(0.86, if days 6-10) or (0.71, if days 11-180)]×[(1.69, if CYP3A5*1/*3 genotype) or (2.00, if CYP3A5*1/*1 genotype)]× (0.70, if receiving a transplant at a steroid sparing centre) × ([age in years/50](-0.4)) × (0.94, if CCB is present). The dose to achieve the desired trough is then prospectively determined using the individuals CL/F estimate. CONCLUSIONS The CYP3A5*1 genotype and four clinical factors were important for tacrolimus CL/F. An individualized dose is easily determined from the predicted CL/F. This study is important towards individualization of dosing in the clinical setting and may increase the number of patients achieving the target concentration. This equation requires validation in an independent cohort of kidney transplant recipients.

MC1R Mutations Modify the Classic Phenotype of Oculocutaneous Albinism Type 2 (OCA2)

The heterogeneous group of disorders known as oculocutaneous albinism (OCA) shares cutaneous and ocular hypopigmentation associated with common developmental abnormalities of the eye. Mutations of at least 11 loci produce this phenotype. The majority of affected individuals develop some cutaneous melanin; this is predominantly seen as yellow/blond hair, whereas fewer have brown hair. The OCA phenotype is dependent on the constitutional pigmentation background of the family, with more OCA pigmentation found in families with darker constitutional pigmentation, which indicates that other genes may modify the OCA phenotype. Sequence variation in the melanocortin-1 receptor (MC1R) gene is associated with red hair in the normal population, but red hair is unusual in OCA. We identified eight probands with OCA who had red hair at birth. Mutations in the P gene were responsible for classic phenotype of oculocutaneous albinism type 2 (OCA2) in all eight, and mutations in the MC1R gene were responsible for the red (rather than yellow/blond) hair in the six of eight who continued to have red hair after birth. This is the first demonstration of a gene modifying the OCA phenotype in humans.

A genome-wide search for allergic response (atopy) genes in three ethnic groups: Collaborative Study on the Genetics of Asthma

Atopy is an IgE-mediated condition known to aggregate in families and is a major risk factor for asthma. As part of the Collaborative Study on the Genetics of Asthma (CSGA), a genome-wide scan for atopy, defined by skin sensitivity to one or more common environmental allergens, was conducted in 287 CSGA families (115 African American, 138 Caucasian and 34 Hispanic). Using a nonparametric genetic analysis approach, two regions were observed in the sample of all families that yielded multipoint lod scores >1.5 (chromosome 11q, lod=1.55 between D11S1986 and D11S1998; chromosome 20p between D20S473 and D20S604, lod=1.54). Modeling that included multiple genomic positions simultaneously indicated that four chromosomal regions accounted for the majority of evidence for linkage in the combined families. These four regions are on chromosomes 10p near D10S1412 (lod=0.94), 11q near D11S1986 (lod=1.76), 17q near D17S784 (lod=0.97) and 20p near D20S473 (lod=1.74). In the subset of pedigrees giving positive evidence for linkage on chromosome 11q, the evidence for linkage increased by lod scores greater than one in four other chromosomal regions: 5q (D5S1480, lod=1.65), 8p (D8S1113, lod=1.60), 12p (D12S372, lod=1.54) and 14q (D14S749, lod=1.70). These results suggest that several regions may harbor genes contributing to the risk for atopy and these may interact with one another in a complex manner.

Variations in the Catechol O-methyltransferase Polymorphism and Prefrontally Guided Behaviors in Adolescents

BACKGROUND The catechol-O-methyltransferase (COMT) gene codes for an enzyme that degrades prefrontal cortex (PFC) synaptic dopamine. Of two identified alleles (Met and Val), the Met allele results in COMT activity that is up to 4 times less pronounced than that conferred by the Val allele, resulting in greater PFC dopamine concentrations. Met-Met homozygotes perform better than individuals who possess the Val allele on PFC-mediated cognitive tasks. These genotypic variations and their associations with executive functions have been described in adults and prepubescent children, but there is a paucity of research assessing these relations in adolescent samples. METHODS In this study, 70 children aged 9-17 were genotyped for COMT and completed measures of working memory, attention, fine motor coordination, and motor speed. RESULTS COMT genotype modulated all but the motor speed measures. The Val-Met genotype was optimal for performance in this adolescent sample. CONCLUSIONS Results are discussed within the context of developmental changes in the dopaminergic system during adolescence.

Pharmacogenetic allele nomenclature: International workgroup recommendations for test result reporting

This article provides nomenclature recommendations developed by an international workgroup to increase transparency and standardization of pharmacogenetic (PGx) result reporting. Presently, sequence variants identified by PGx tests are described using different nomenclature systems. In addition, PGx analysis may detect different sets of variants for each gene, which can affect interpretation of results. This practice has caused confusion and may thereby impede the adoption of clinical PGx testing. Standardization is critical to move PGx forward.

The Pigmentary System: Physiology and Pathophysiology: Second Edition

The most comprehensive and integrated book on pigmentation. The Pigmentary System, Second Edition, gathers into one convenient, all-inclusive volume a wealth of information about the science of pigmentation and all the common and rare clinical disorders that affect skin color. The two parts, physiology (science) and pathophysiology (clinical disorders), are complementary and annotated so that those reading one part can easily refer to relevant sections in the other. For the clinician interested in common or rare pigment disorders or the principles of teaching about such disorders, this book provides an immediate and complete resource on the biologic bases for these disorders. For the scientist studying the biology of melanocyte function, the book provides a list of disorders that are related to basic biological functions of melanocytes. New features of this Second Edition include: Completely new section on the basic science of pigmentation explaining the integration of melanocyte functions with other epidermal cells and with various organ systems like the immune system. New chapters on pigmentary disorders related to intestinal diseases, the malignant melanocyte, benign proliferations of melanocytes (nevi) and phototherapy with narrow band UV. All clinical chapters include the latest genetic findings and advances in therapy. More than 400 color images of virtually all clinical disorders. The book is ideal for all dermatologists and especially those interested in disorders of pigmentation. It is of particular use for pediatric dermatologists and medical geneticists caring for patients with congenital and genetic pigmentary disorders. This authoritative volume will fill the gap for dermatology training programs that do not have local experts on pigmentation. Basic and cosmetic scientists studying pigmentation and melanocytes will find the science and clinical correlations very useful in showing human significance and relevance to the results of their studies.

The minnesota center for twin and family research genome-wide association study

As part of the Genes, Environment and Development Initiative, the Minnesota Center for Twin and Family Research (MCTFR) undertook a genome-wide association study, which we describe here. A total of 8,405 research participants, clustered in four-member families, have been successfully genotyped on 527,829 single nucleotide polymorphism (SNP) markers using llluminas Human660W-Ouad array. Quality control screening of samples and markers as well as SNP imputation procedures are described. We also describe methods for ancestry control and how the familial clustering of the MCTFR sample can be accounted for in the analysis using a Rapid Feasible Generalized Least Squares algorithm. The rich longitudinal MCTFR assessments provide numerous opportunities for collaboration.