No abstract

Friedreich ataxia (FRDA) is an autosomal recessive neurodegenerative disorder caused by GAA triplet expansions or point mutations in the FXN gene on chromosome 9q13. The gene product called frataxin, a mitochondrial protein that is severely reduced in FRDA patients, leads to mitochondrial iron accumulation, FeS cluster deficiency and oxidative damage. The tissue specificity of this mitochondrial disease is complex and poorly understood. While frataxin is ubiquitously expressed, the cellular phenotype is most severe in neurons and cardiomyocytes. Here, we conducted comprehensive proteomic, metabolic and functional studies to determine whether subclinical abnormalities exist in mitochondria of blood cells from FRDA patients. Frataxin protein levels were significantly decreased in platelets and peripheral blood mononuclear cells from FRDA patients. Furthermore, the most significant differences associated with frataxin deficiency in FRDA blood cell mitochondria were the decrease of two mitochondrial heat shock proteins. We did not observe profound changes in frataxin-targeted mitochondrial proteins or mitochondrial functions or an increase of apoptosis in peripheral blood cells, suggesting that functional defects in these mitochondria are not readily apparent under resting conditions in these cells.

The ability of mice deficient in galactose-1-phosphate uridyltransferase (GALT) to metabolize galactose was determined in animals weaned to a mouse chow diet for a 4-wk period. When given [14 C]galactose intraperitoneally, these animals slowly oxidized the sugar, excreting only 5.5% of the dose as 14 CO 2 in 4 h, whereas normal animals excreted 39.9%. These results mimic those seen in human galactosemic patients given isotopic galactose. When given 10 mol of [1-13 C]galactose, normal animals excrete small amounts of labeled galactose and galactonate but no galactitol in urine whereas GALT-deficient mice excrete significant amounts of all of these as labeled compounds in urine. When challenged with galactose, only about 20% of the dose is excreted in urine, and even on the chow diet, significant amounts of galactose, galactonate, and galactitol are excreted in urine. These compounds are also found to be present in liver, kidney, and brain, except that galactonate is not found in brain. Galactose-1-phosphate accumulates in red blood cells to levels found in humans exposed to large amounts of galactose, and galactose-1-phosphate is found in increased amounts in liver, kidney, and brain of GALT-deficient animals. There was no difference in the hepatic concentration of uridine diphosphate galactose and uridine diphosphate glucose between normal and GALT-deficient mice. The explanation for the presence of galactose and its conversion products in tissues and urine of affected mice appears to be related to the presence of approximately 1.75% of galactose-containing carbohydrates in the chow, which becomes bioavailable to mice. Despite the presence of galactose and its metabolites in tissues and urine and impaired ability to oxidize the sugar, the GALT-deficient animals are indistinguishable from normal animals and do not exhibit the phenotype of humans with GALT-deficiency galactosemia. Abbreviations GALT, galactose-1-phosphate uridyltransferase Gal-1-P, galactose-1-phosphate N/N, normal mice G/N, heterozygous normal and GALT deficient G/G, homozygous for a deficiency of GALT UDPgal, uridine diphosphate galactose UDPglu, uridine diphosphate glucose BSTFA, N,O-bis-(trimethylsilyl)trifluoroacetamide TMCS, trimethylchlorosilane CHOP, Children's Hospital of Philadelphia GC-MS, gas chromatography-mass spectroscopy After more than 60 y of experience with the diagnosis and dietary therapy of galactosemia caused by GALT deficiency, the pathophysiology of the disorder has remained unclear (1). Enigmatic has been the origin of both the rapid development of liver, kidney, eye, and central nervous toxicity occurring in newborns exposed to large amounts of galactose in milk and the long-term diet-independent complications of cognitive impairment, speech and learning disorders, ataxia, and primary ovarian failure in females. To enhance the study of the pathogenesis of GALT deficiency and further our understanding of the cause of the galactosemic phenotype, we made mice deficient in GALT activity using gene-targeting techniques (2).We...