Mechanisms of myopia in Cohen syndrome mapped to chromosome 8q22.

PURPOSE: To analyze the mechanisms of myopia in Cohen syndrome (Mendelian Inheritance in Man [MIM] no. 216550). METHODS: A cross-sectional study of 22 Finnish patients (age range, 2-57 years) with Cohen syndrome, which maps to chromosome 8q22, was undertaken to record cycloplegic refraction, keratometry (corneal power and radius of curvature), biometry (anterior chamber depth [ACD], lens thickness [LT], axial [AL] and vitreal length [VL]), and Hoffer Q-modeled lens power. These components of refraction were correlated to age and spherical equivalent (SE) at the corneal plane. Contribution to total myopia of refractive (corneal and lenticular) and axial components was modeled by multiple linear regression and by estimating the effect of deviation from population mean values. RESULTS: The mean SE in patients with Cohen syndrome older than 10 years was -9.35 D; the mean cylinder power, +1.70 D; and the mean anisometropia, 0.53 D. Relative to the emmetropic eye of a young adult, the AL and VL (mean, 23.9 and 16.6 mm, respectively) and lens power (mean, 30.30 D) were higher in 74% and 93% of patients, respectively, and the ACD (mean, 2.5 mm) was smaller and the LT (mean, 4.9 mm) and corneal power (mean, 45.63 D) higher than average in all patients. Corneal power (r = 0.513, P = 0.021) increased with age, but AL and VL (P = 0.46 and 0.54, respectively) and lens power (P = 0.89) did not correlate with age. The lens power decreased with AL (r = -0.564, P = 0.029) and tended to increase with corneal power (r = 0.475, P = 0.074). Multiple linear regression identified AL and corneal power as independent predictors of SE. Based on deviation from population means, the lens power explained 55%, corneal power 23%, and AL 22% of total myopia. ACD decreased and LT increased markedly with age, rendering angle-closure glaucoma a possibility. CONCLUSIONS: Myopia in Cohen syndrome is mainly refractive in type and is due to high corneal and lenticular power, which is otherwise rare in young patients. It may be superimposed on axial myopia, probably related to polygenic factors that determine myopia in the general population. The refractive myopia in Cohen syndrome may result from dysgenesis and atrophy of the cornea, ciliary body, and iris, which in turn cause iridial and zonular laxity and spherophakia.

Finnish Disease Heritage I: characteristics, causes, background.

This review of the Finnish Disease Heritage (FDH), a group of rare hereditary diseases that are overrepresented in Finland, includes the following topics: FDH characteristics, causes and background, primary theory, revis(it)ed theory, consanguineous marriages in Finland, internal migration of the 1500s, family series for further FDH studies, geography and population structure as a basis for FDH, geography of individual diseases, the structure of FDH families, family structure in individual diseases, Finnish gene mutations, linkage disequilibrium and haplotypes, age of gene mutations, frequencies of disease genes and carriers, and a short description of the possible future of FDH.

Finnish Disease Heritage II: population prehistory and genetic roots of Finns.

In the second part of my review of the Finnish Disease Heritage (FDH), I discuss the settling of Finland; factors influencing the genes of a population, such as agriculture versus hunting/fishing/gathering, trading and cultural relations, wars and other kinds of violence, and bottlenecks; relatives of the Finns in the light of classical European studies, classical Finnish studies, mtDNA and Y-chromosomal studies; the genes of the Finns today, characterizing FDH, the east-west difference among Finns, and minorities in Finland, viz. the Lapps or Saami and Swedish-speaking Finns.

The Finnish Disease Heritage III: the individual diseases.

This article is the third and last in a series entitled The Finnish Disease Heritage I-III. All the 36 rare hereditary diseases belonging to this entity are described for clinical and molecular genetic purposes, based on the Finnish experience gathered over a period of half a century. In addition, five other diseases are mentioned. They may be included in the list of the "Finnish diseases" after adequate complementary studies.

Cohen syndrome is caused by mutations in a novel gene, COH1, encoding a transmembrane protein with a presumed role in vesicle-mediated sorting and intracellular protein transport.

Cohen syndrome is an uncommon autosomal recessive disorder whose diagnosis is based on the clinical picture of nonprogressive psychomotor retardation and microcephaly, characteristic facial features, retinal dystrophy, and intermittent neutropenia. We have refined the critical region on chromosome 8q22 by haplotype analysis, and we report the characterization of a novel gene, COH1, that is mutated in patients with Cohen syndrome. The longest transcript (14,093 bp) is widely expressed and is transcribed from 62 exons that span a genomic region of approximately 864 kb. COH1 encodes a putative transmembrane protein of 4,022 amino acids, with a complex domain structure. Homology to the Saccharomyces cerevisiae VPS13 protein suggests a role for COH1 in vesicle-mediated sorting and transport of proteins within the cell.

Delineation of Cohen syndrome following a large-scale genotype-phenotype screen.

Cohen syndrome is an autosomal recessive condition associated with developmental delay, facial dysmorphism, pigmentary retinopathy, and neutropenia. The pleiotropic phenotype, combined with insufficient clinical data, often leads to an erroneous diagnosis and has led to confusion in the literature. Here, we report the results of a comprehensive genotype-phenotype study on the largest cohort of patients with Cohen syndrome assembled to date. We found 22 different COH1 mutations, of which 19 are novel, in probands identified by our diagnostic criteria. In addition, we identified another three novel mutations in patients with incomplete clinical data. By contrast, no COH1 mutations were found in patients with a provisional diagnosis of Cohen syndrome who did not fulfill the diagnostic criteria ("Cohen-like" syndrome). This study provides a molecular confirmation of the clinical phenotype associated with Cohen syndrome and provides a basis for laboratory screening that will be valuable in its diagnosis.

Comparative PRKAR1A genotype-phenotype analyses in humans with Carney complex and prkar1a haploinsufficient mice.

Carney complex (CNC) is a familial multiple neoplasia syndrome characterized by cardiac and extracardiac myxomas in the setting of spotty skin pigmentation and endocrinopathy. We previously identified PRKAR1A (regulatory subunit 1alpha of protein kinase A) mutations in CNC. Mutational analyses of the PRKAR1A gene in 51 unrelated CNC probands now detect mutations in 65%. All mutations, except for one unique missense mutation, lead to PRKAR1A haploinsufficiency. Therefore, we studied the consequences of prkar1a haploinsufficiency in mice. Although we did not observe cardiac myxomas or altered pigmentation in prkar1a(+/-) mice, we did observe some phenotypes similar to CNC, including altered heart rate variability. Moreover, prkar1a(+/-) mice exhibited a marked propensity for extracardiac tumorigenesis. They developed sarcomas and hepatocellular carcinomas. Sarcomas were frequently associated with myxomatous differentiation. Tumors from prkar1a(+/-) mice did not exhibit prkar1a loss of heterozygosity. Thus, we conclude that although PRKAR1A haploinsufficiency does predispose to tumorigenesis, distinct secondary genetic events are required for tumor formation.