Mutations in DHDPSL are responsible for primary hyperoxaluria type III

Abstract

Primary hyperoxaluria (PH) is an autosomal-recessive disorder of endogenous oxalate synthesis characterized by accumulation of calcium oxalate primarily in the kidney. Deficiencies of alanine-glyoxylate aminotransferase (AGT) or glyoxylate reductase (GRHPR) are the two known causes of the disease (PH I and II, respectively). To determine the etiology of an as yet uncharacterized type of PH, we selected a cohort of 15 non-PH I/PH II patients from eight unrelated families with calcium oxalate nephrolithiasis for high-density SNP microarray analysis. We determined that mutations in an uncharacterized gene, DHDPSL, on chromosome 10 cause a third type of PH (PH III). To overcome the difficulties in data analysis attributed to a state of compound heterozygosity, we developed a strategy of "heterozygosity mapping"-a search for long heterozygous patterns unique to all patients in a given family and overlapping between families, followed by reconstruction of haplotypes. This approach enabled us to determine an allelic fragment shared by all patients of Ashkenazi Jewish descent and bearing a 3 bp deletion in DHDPSL. Overall, six mutations were detected: four missense mutations, one in-frame deletion, and one splice-site mutation. Our assumption is that DHDPSL is the gene encoding 4-hydroxy-2-oxoglutarate aldolase, catalyzing the final step in the metabolic pathway of hydroxyproline.

Figure 1

Alleles of Ashkenazi Jewish Families (A) Pedigrees of families 1, 2, 11, and 12, which enabled us to identify DHDPSL and the pattern of adjacent SNPs. (B) Distribution of the shared allele among Ashkenazi Jewish families. Black numbers indicate the length of the shared fragment, red numbers indicate the length of the homozygous fragment, and the pink frame indicates the common fragment J. The lengths of the fragments are presented in megabase pairs.

Figure 2

DNA Sequencing of an Amplicon of Exon 7 of DHDPSL Demonstrating the Deletion Mutation c.944_946delAGG Found in All Ashkenazi Jewish Patients and Two Additional Families The red box marks the deletion. (Note: SNP rs1124116 upstream of exon 7 should be avoided in designing primers.)

Figure 3

The Metabolic Pathways of Oxalate Production in Humans

Figure 4

The Metabolic Pathway of Hydroxyproline Degradation in Humans

Figure 5

Comparison of Amino Acid Composition of DHDPSL and 4-Hydroxy-2-Oxoglutarate Aldolase Blue, protein encoded by the bovine DHDPSL (0P515) lacking the mitochondrial localization signal; red, 4-hydroxy-2-oxoglutarate aldolase.