Visual Analytics for Hypothesis-Driven Exploration in Computational Pathology

Recent advances in computational and algorithmic power are evolving the field of medical imaging rapidly. In cancer research, many new directions are sought to characterize patients with additional imaging features derived from radiology and pathology images. The emerging field of Computational Pathology targets the high-throughput extraction and analysis of the spatial distribution of cells from digital histopathology images. The associated morphological and architectural features allow researchers to quantify and characterize new imaging biomarkers for cancer diagnosis, prognosis, and treatment decisions. However, while the image feature space grows, exploration and analysis become more difficult and ineffective. There is a need for dedicated interfaces for interactive data manipulation and visual analysis of computational pathology and clinical data. For this purpose, we present IIComPath, a visual analytics approach that enables clinical researchers to formulate hypotheses and create computational pathology pipelines involving cohort construction, spatial analysis of image-derived features, and cohort analysis. We demonstrate our approach through use cases that investigate the prognostic value of current diagnostic features and new computational pathology biomarkers.

GeneSeeker: extraction and integration of human disease-related information from web-based genetic databases

The identification of genes underlying human genetic disorders requires the combination of data related to cytogenetic localization, phenotypes and expression patterns, to generate a list of candidate genes. In the field of human genetics, it is normal to perform this combination analysis by hand. We report on GeneSeeker (), a web server that gathers and combines data from a series of databases. All database searches are performed via the web interfaces provided with the original databases, guaranteeing that the most recent data are queried, and obviating data warehousing. GeneSeeker makes the same selection of candidate genes as the human geneticists would have performed, and thus reducing the time-consuming process to a few minutes. GeneSeeker is particularly well suited for syndromes in which the disease gene displays altered expression patterns in the affected tissue(s).

Mutations in a human homologue of Drosophila crumbs cause retinitis pigmentosa (RP12)

Retinitis pigmentosa (RP) comprises a clinically and genetically heterogeneous group of diseases that afflicts approximately 1.5 million people worldwide. Affected individuals suffer from a progressive degeneration of the photoreceptors, eventually resulting in severe visual impairment. To isolate candidate genes for chorioretinal diseases, we cloned cDNAs specifically or preferentially expressed in the human retina and the retinal pigment epithelium (RPE) through a novel suppression subtractive hybridization (SSH) method. One of these cDNAs (RET3C11) mapped to chromosome 1q31-q32.1, a region harbouring a gene involved in a severe form of autosomal recessive RP characterized by a typical preservation of the para-arteriolar RPE (RP12; ref. 3). The full-length cDNA encodes an extracellular protein with 19 EGF-like domains, 3 laminin A G-like domains and a C-type lectin domain. This protein is homologous to the Drosophila melanogaster protein crumbs (CRB), and denoted CRB1 (crumbs homologue 1). In ten unrelated RP patients with preserved para-arteriolar RPE, we identified a homozygous AluY insertion disrupting the ORF, five homozygous missense mutations and four compound heterozygous mutations in CRB1. The similarity to CRB suggests a role for CRB1 in cell-cell interaction and possibly in the maintenance of cell polarity in the retina. The distinct RPE abnormalities observed in RP12 patients suggest that CRB1 mutations trigger a novel mechanism of photoreceptor degeneration.

Isolation and mapping of novel candidate genes for retinal disorders using suppression subtractive hybridization

We have constructed human cDNA libraries enriched for retina- and retinal pigment epithelium (RPE)/choroid-specific cDNAs through suppression subtractive hybridization. The sequence of 314 cDNAs from the retina enriched library and 126 cDNAs from the RPE/choroid enriched library was analyzed. Based on the absence of a database match, 25% of the retina cDNA clones and 16% of the RPE/choroid cDNA clones are novel cDNAs. The expression profiles of 86 retina and 21 RPE/choroid cDNAs were determined by a semiquantitative reverse transcription polymerase chain reaction technique. Thirty-three cDNAs were expressed exclusively or most prominently in retina or RPE/choroid. These cDNAs were mapped in the human genome by radiation hybrid mapping. Eleven cDNAs colocalized with loci involved in retinal disorders. One cDNA mapped in a 1.5-megabase critical region for autosomal recessive retinitis pigmentosa (RP12). Another cDNA was assigned to the 7.7-cM RP17 linkage interval. Seven cDNAs colocalized with four loci involved in Bardet-Biedl syndrome.

The 2588G-->C mutation in the ABCR gene is a mild frequent founder mutation in the Western European population and allows the classification of ABCR mutations in patients with Stargardt disease

In 40 western European patients with Stargardt disease (STGD), we found 19 novel mutations in the retina-specific ATP-binding cassette transporter (ABCR) gene, illustrating STGD's high allelic heterogeneity. One mutation, 2588G-->C, identified in 15 (37.5%) patients, shows linkage disequilibrium with a rare polymorphism (2828G-->A) in exon 19, suggesting a founder effect. The guanine at position 2588 is part of the 3' splice site of exon 17. Analysis of the lymphoblastoid cell mRNA of two STGD patients with the 2588G-->C mutation shows that the resulting mutant ABCR proteins either lack Gly863 or contain the missense mutation Gly863Ala. We hypothesize that the 2588G-->C alteration is a mild mutation that causes STGD only in combination with a severe ABCR mutation. This is supported in that the accompanying ABCR mutations in at least five of eight STGD patients are null (severe) and that a combination of two mild mutations has not been observed among 68 STGD patients. The 2588G-->C mutation is present in 1 of every 35 western Europeans, a rate higher than that of the most frequent severe autosomal recessive mutation, the cystic fibrosis conductance regulator gene mutation DeltaPhe508. Given an STGD incidence of 1/10,000, homozygosity for the 2588G-->C mutation or compound heterozygosity for this and other mild ABCR mutations probably does not result in an STGD phenotype.

ABCR unites what ophthalmologists divide(s)

Over the last years, the molecular causes of monogenic chorioretinal diseases have been elucidated at an increasing pace. In contrast, only recently have genetic factors been found that contribute to multifactorial eye disorders such as age-related macular degeneration (AMD). Mutations in the retina-specific ATP-binding cassette transporter gene (ABCR) cause recessive Stargardt's disease (STGD) and fundus flavimaculatus (FFM), and were also found in 16% of patients with AMD. In addition, ABCR mutations were identified in families with recessive retinitis pigmentosa (RP), cone dystrophy (COD), and cone-rod dystrophy (CRD). In this review, we summarize these findings and propose a model which provides a framework to explain the observed genotypes and phenotypes. We hypothesize that most ABCR mutations can be classified in different classes of severity, and that, depending on the remaining total activity of ABCR, the phenotype can range from AMD at the mild end to RP at the severe end of the spectrum. This model allows us to make several predictions on the type and/or severity of ABCR mutations that are present in patients with AMD, STGD/FFM, COD, CRD, and RP.