Assignment of the structural gene for argininosuccinate synthetase to proximal mouse chromosome 2

Contrasting features of urea cycle disorders in human patients and knockout mouse models

The urea cycle exists for the removal of excess nitrogen from the body. Six separate enzymes comprise the urea cycle, and a deficiency in any one of them causes a urea cycle disorder (UCD) in humans. Arginase is the only urea cycle enzyme with an alternate isoform, though no known human disorder currently exists due to a deficiency in the second isoform. While all of the UCDs usually present with hyperammonemia in the first few days to months of life, most disorders are distinguished by a characteristic profile of plasma amino acid alterations that can be utilized for diagnosis. While enzyme assay is possible, an analysis of the underlying mutation is preferable for an accurate diagnosis. Mouse models for each of the urea cycle disorders exist (with the exception of NAGS deficiency), and for almost all of them, their clinical and biochemical phenotypes rather closely resemble the phenotypes seen in human patients. Consequently, all of the current mouse models are highly useful for future research into novel pharmacological and dietary treatments and gene therapy protocols for the management of urea cycle disorders.

Breakpoint characterization of der(9) deletions in chronic myeloid leukemia patients

Deletions adjacent to the 9/22 translocation breakpoint on the derivative chromosome 9 have recently been described in a substantial number of chronic myeloid leukemia (CML) cases, but their extension has not been characterized in detail. Using FISH with an appropriate set of BAC/PAC probes, we have characterized the deletion in 10 CML cases, identified by screening 71 patients at diagnosis. Five patients showed a complex chromosome rearrangement and 3 of them were deleted. The size of the deletion was variable, ranging from few hundreds kb to 8 Mb. A minimally deleted region on both chromosomes 9 and 22 was identified and was found to contain the ASS gene on chromosome 9 and IGLL1 on chromosome 22.

Transcriptional regulation of genes for ornithine cycle enzymes

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Generation of a mouse model for citrullinemia by targeted disruption of the argininosuccinate synthetase gene

Argininosuccinate synthetase (ASS) is a urea cycle enzyme that forms argininosuccinate from citrulline and aspartate. Mutations at the ASS locus in man cause the inherited disease, citrullinemia. Citrullinemia is inherited as an autosomal recessive trait and is characterized, biochemically, by elevated levels of blood citrulline and ammonia and often results in early neonatal death if untreated. We have used homologous recombination in embryonic stem cells to generate a line of mice having a targeted disruption of the Ass gene. Homozygous mutant animals develop high levels of blood citrulline, become hyperammonemic, and die within one or two days after birth. Because the phenotype of the mutant mice closely resembles that of humans who lack the ASS enzyme, we expect that these mice will serve as a useful model for exploring new treatments for citrullinemia including somatic gene therapy.