Genes and inheritance.

The information gained from the Human Genome Project and related genetic research will undoubtedly create significant changes in health care practice. It is becoming increasing clear that nurses in all areas of clinical practice will require a fundamental understanding of basic genetics. This self-learning module provides the oncology nurse with an overview of basic genetic concepts including inheritance patterns of single gene conditions, pedigree construction, chromosome aberrations, and the multifactorial basis underlying many common diseases of adulthood. Normal gene structure and function will be introduced and the biochemistry of genetic errors will be described.

A second locus for hereditary hemorrhagic telangiectasia maps to chromosome 12.

Hereditary hemorrhagic telangiectasia (HHT) or Osler-Rendu-Weber (ORW) disease is an autosomal dominant vascular dysplasia. Initial linkage studies identified an ORW gene localized to 9q33-q34 but with some families clearly excluding this region. A probable correlation in clinical phenotype between the 9q3-linked families and unlinked families was described with a significantly lower incidence of pulmonary arteriovenous malformations observed in the unlinked families. In this study we examined four unrelated ORW families for which linkage to chromosome 9q33-q34 has been previously excluded. Linkage was established for all four families to markers on chromosome 12, with a combined maximum lod score of 10.77 (theta = 0.04) with D12S339. Mapping of crossovers using haplotype analysis indicated that the candidate region lies in an 11-CM interval between D12S345 and D12S339, in the pericentromeric region of chromosome 12. A map location for a second ORW locus is thus established that exhibits a significantly reduced incidence of pulmonary involvement.

A gene for familial venous malformations maps to chromosome 9p in a second large kindred.

Venous malformations are a common form of vascular anomaly that cause pain and disfigurement and can be life threatening if they involve critical organs. They occur sporadically or in a familial form, where multiple lesions are usually present. We have identified a large kindred showing autosomal dominant inheritance of venous malformations. Using this family we confirm linkage of a familial form of venous malformations to chromosome 9p. We suggest that blue rubber bleb naevus syndrome can be considered a particular manifestation of this form of familial venous malformations. The candidate region for this gene encompasses the interferon gene cluster and the MTS1 (p16) tumour suppressor gene.

Genetic heterogeneity in hereditary haemorrhagic telangiectasia: possible correlation with clinical phenotype.

Hereditary haemorrhagic telangiectasia (HHT) or Osler-Weber-Rendu syndrome is an autosomal dominant vascular dysplasia characterised by recurrent haemorrhage. Our initial linkage studies found an HHT gene to be localised to 9q3 in two large kindreds. In the present study, we examine an additional five unrelated HHT families. Linkage analysis in this region resulted in a peak multipoint location score of 13.03, 10 cM proximal of D9S60. We found significant evidence for heterogeneity of HHT. Multipoint analysis supports the family specific two point studies with odds of 3,000,000:1 showing linkage and heterogeneity over linkage and homogeneity. Four of the seven families give a posterior probability of > 99% of being of the linked type, and three families appear unlinked to this region of 9q, and by multipoint analysis completely exclude the candidate region for HHT. Two new crossovers in affected persons in one of the linked families further define the proximal border of the candidate region on 9q3. A possible correlation in clinical phenotype between the 9q3 linked families and unlinked families is described. Although six of the seven families clearly meet the clinical criteria for HHT diagnosis, a significant absence of pulmonary arteriovenous malformations is seen in all three 9q3 unlinked families. Genetic heterogeneity of HHT and its potential correlation with a clinical phenotype may have a significant impact on the clinical management and treatment of HHT patients.

Endoglin, a TGF-beta binding protein of endothelial cells, is the gene for hereditary haemorrhagic telangiectasia type 1.

Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant disorder characterized by multisystemic vascular dysplasia and recurrent haemorrhage. Linkage for some families has been established to chromosome 9q33-q34. In the present study, endoglin, a transforming growth factor beta (TGF-beta) binding protein, was analysed as a candidate gene for the disorder based on chromosomal location, expression pattern and function. We have identified mutations in three affected individuals: a C to G substitution converting a tyrosine to a termination codon, a 39 base pair deletion and a 2 basepair deletion which creates a premature termination codon. We have identified endoglin as the HHT gene mapping to 9q3 and have established HHT as the first human disease defined by a mutation in a member of the TGF-beta receptor complex.

A disease locus for hereditary haemorrhagic telangiectasia maps to chromosome 9q33-34.

Hereditary haemorrhagic telangiectasia (HHT), or Osler-Weber-Rendu disease, is an autosomal dominant vascular dysplasia of unknown pathogenesis leading to 'widespread' dermal, mucosal and visceral telangiectases and recurrent haemorrhage. We have mapped the HHT gene, by linkage analysis, to markers on 9q33-34 in two large multi-generation families. Haplotype analysis and mapping of recombination breakpoints gives a 4 cM interval between D9S61 and D9S63 as the most likely location of the gene. The closest marker, D9S65, is estimated to be within 1 cM of the gene and shows a combined lod score of 11.41. Two potential candidate genes, COL5A1 and ZNF79, are also located within 9q33-34. These results provide a starting point for the eventual cloning of the HHT gene.

BRCA1 maps proximal to D17S579 on chromosome 17q21 by genetic analysis.

Previous studies have demonstrated linkage between early-onset breast cancer and ovarian cancer and genetic markers on chromosome 17q21. These markers define the location of a gene (BRCA1) which appears to be inherited as an autosomal dominant susceptibility allele. We analyzed five families with multiple affected individuals for evidence of linkage to the BRCA1 region. Two of the five families appear to be linked to BRCA1. One apparently linked family contains critical recombinants, suggesting that the gene is proximal to the marker D17S579 (Mfd188). These findings are consistent with the maximum-likelihood position estimated by the Breast Cancer Linkage Consortium and with recombination events detected in other linked families. Linkage analysis was greatly aided by PCR-based analysis of paraffin-embedded normal breast tissue from deceased family members, demonstrating the feasibility and importance of this approach. One of the two families with evidence of linkage between breast cancer and genetic markers flanking BRCA1 represents the first such family of African-American descent to be reported in detail.