Wendy S. Rubinstein

Phenotypic dichotomy in mitochondrial complex II genetic disorders

This review presents our current knowledge on the genetic and phenotypic aspects of mitochondrial complex II gene defects. The mutations of the complex II subunits cause two strikingly different group of disorders, revealing a phenotypic dichotomy. Genetic disorders of the mitochondrial respiratory chain are often characterized by hypotonia, growth retardation, cardiomyopathy, myopathy, neuropathy, organ failure, and metabolic derangement. These disorders are transmitted through maternal lineage if the defective gene is located in the mitochondrial genome or may follow a Mendelian pattern if it is in the nucleus. Mitochondrial complex II (succinate:ubiquinone oxidoreductase) is the smallest complex in the respiratory chain and is composed of four subunits encoded by nuclear genes SDHA, SDHB, SDHC, and SDHD. Complex II oxidizes succinate to fumarate in the Krebs cycle and is involved in the mitochondrial electron transport chain. SDHA and SDHB encode the flavoprotein and iron-sulfur proteins, respectively, and SDHC and SDHD encode the two hydrophobic membrane-spanning subunits. While mutations in SDHA display a phenotype resembling other mitochondrial and Krebs cycle gene defects, those in SDHB, SDHC and SDHD cause hereditary paraganglioma. Paraganglioma is characterized by slow-growing vascular tumors of the paraganglionic tissue (i.e., adrenal and extra-adrenal paragangliomas, including those in the head and neck, mediastinum, abdomen, and pheochromocytomas). Paraganglioma caused by SDHD mutations occurs exclusively after paternal transmission, suggesting that genomic imprinting influences gene expression. Association of a mitochondrial gene defect with tumorigenesis expands the phenotypic spectrum of mitochondrial diseases and adds genomic imprinting as a new transmission mode in mitochondrial genetics. The phenotypic features of complex II gene mutations suggest that whereas the catalytic subunit SDHA mutations may compromise the Krebs cycle, those in other structural subunits may affect oxygen sensing and signaling.

Repositioning the hereditary paraganglioma critical region on chromosome band 11q23

Abstract Hereditary paragangliomas (PGL, glomus tumors, MIM no.168000) are mostly benign, slow-growing tumors of the head and neck region. The gene (or genes) affecting risk to PGL are subject to genomic imprinting: children of affected fathers exhibit an autosomal dominant pattern of disease inheritance, whereas children of affected mothers rarely if ever develop the disease through maternal transmission. We previously confined the disease gene to an approximately 6 Mb critical region on chromosome band 11q23 (PGL1). Based on haplotype analysis of an extended Dutch pedigree, a 2 Mb sub-region between D11S938 and D11S1885 was proposed as the PGL1 critical interval. In this study, we excluded this interval by analysis of two new single tandem repeat polymorphisms (STRP) contained therein. Instead, we predicted a non-overlapping, more proximal 2 Mb critical interval between D11S1647 and D11S897, and evaluated this new region using nine STRP (D11S1986, five new, closely-linked STRP, D11S1347, D11S3178, and D11S1987). Consistent with our prediction, we observed substantial haplotype-sharing within the Dutch pedigree. We also analyzed four new American PGL families. A recombination event detected in one family further defined D11S1347 as the new telomeric border. We observed significant haplotype-sharing within this new interval among three unrelated American PGL families, strongly suggesting that they originated from a common ancestor. Thus, we confined PGL1 to an approximately 1.5 Mb region between D11S1986 and D11S1347, and showed identity-by-descent sharing for a group of American PGL families.

Proportion of Heritable Paraganglioma Cases and Associated Clinical Characteristics

Objective/Hypothesis To determine the heritable proportion of paraganglioma (PGL) and identify clinical features associated with heritable PGL.

Use of indium-111-labeled hepatocytes to determine the biodistribution of transplanted hepatocytes through portal vein infusion.

PURPOSE Hepatocyte transplantation is useful for ex vivo gene therapy and liver repopulation. Methods for hepatic reconstitution were recently developed, but hepatocyte transplantation systems must be optimized. The authors report their experience with In-111 oxyquinolone labeling of a test dose of hepatocytes (108 cells) for noninvasive assessment of the biodistribution of transplanted hepatocytes in a 5-year-old child with omithine transcarbamoylase deficiency. MATERIALS AND METHODS Donor hepatocytes (approximately 108) were radiolabeled using a commercially available In-111 oxyquinolone solution (specific activity of 1 mCi/ml). RESULTS The overall labeling efficiency was 36.4%. A final dose of approximately 290 ,uCi of the In-111-labeled hepatocytes in 10 ml serum-free phosphate-buffered saline was infused percutaneously into the portal vein approximately 2.5 hours after their preparation. The study was performed 3 hours before cell transplantation (109 cells). Quantitative analysis of the biodistribution of In-111-labeled hepatocytes indicated that cells were predominantly localized in the liver immediately after portal vein-infused transplantation. The predominant hepatic distribution was persistent for as long as 7 days after the procedure, with an average liver-to-spleen ratio of 9.5 to 1. No significant pulmonary radiotracer uptake was present. CONCLUSION These results indicate that In-111 labeling of hepatocytes is useful for the short-term noninvasive analysis of the biodistribution of transplanted hepatocytes.

Qualitative Cancer Genetic Counseling Research, Part II: Findings from a Exploratory Ethnographic Study in a Cancer Clinic

This is a report of the preliminary findings of a brief exploratory ethnographic study in a cancer diagnosis and treatment clinic. The main research purpose was to explore the meaning of cancer and cancer treatment to patients themselves and to their relatives and close friends. The methods are described in detail in a paper focusing on the experiences of being a novice ethnographer (Peters et al. (2001) J Genet Counsel 10(2):133–150.). The preliminary results of this exploratory fieldwork indicate that the experience of attending a cancer treatment clinic for evaluation and/or treatment is a complex social, emotional as well as medical process for patients and families. Themes with relevance to genetic counselors that emerged from this early observation period included ideas about causes of cancer, the complex nature of families and kinship, coping and support, use of food, and healing. These initial findings have implications for genetic counseling practice and hopefully will stimulate more qualitative social and behavioral research in cancer genetic counseling.

Interstitial lung disease in an adult with Fanconi anemia: Clues to the pathogenesis

We have studied a 38-year-old man with a prior diagnosis of Holt-Oram syndrome, who presented with diabetes mellitus. He had recently taken prednisone for idiopathic interstitial lung disease and trimethoprim-sulfamethoxazole for sinusitis. Thrombocytopenia progressed to pancytopenia. The patient had skeletal, cardiac, renal, cutaneous, endocrine, hepatic, neurologic, and hematologic manifestations of Fanconi anemia (FA). Chest radiographs showed increased interstitial markings at age 25, dyspnea began in his late 20s, and he stopped smoking at age 32. At age 38, computerized tomography showed bilateral upper lobe fibrosis, lower lobe honeycombing, and bronchiectasis. Pulmonary function tests, compromised at age 29, showed a moderately severe obstructive and restrictive pattern by age 38. Serum alpha-1 antitrypsin level was 224 (normal 85-213) mg/dL and PI phenotype was M1. Karyotype was 46,XY with a marked increase in chromosome aberrations induced in vitro by diepoxybutane. The early onset and degree of pulmonary disease in this patient cannot be fully explained by environmental or known genetic causes. The International Fanconi Anemia Registry (IFAR) contains no example of a similar pulmonary presentation. Gene-environment (ecogenetic) interactions in FA seem evident in the final phenotype. The pathogenic mechanism of lung involvement in FA may relate to oxidative injury and cytokine anomalies.