Two novel AGXT mutations identified in primary hyperoxaluria type-1 and distinct morphological and structural difference in kidney stones

Abstract

Primary hyperoxaluria type 1 (PH1) is a rare genetic disease characterized by excessive oxalate accumulation in plasma and urine, resulting in various phenotypes because of allelic and clinical heterogeneity. This study aimed to detect disease-associated genetic mutations in three PH1 patients in a Chinese family. All AGXT exons and 3 common polymorphisms which might synergistically interact with mutations, including P11L, I340 M and IVSI+74 bp were analyzed by direct sequencing in all family members. It demonstrated that in each of three patients, a previously reported nonsense mutation p.R333(*) was in cis with a novel missense mutation p.M49L in the minor allele characterized by the polymorphism of 74-bp duplication in intron 1, while the other novel missense mutation p.N72I was in trans with both p.R333(*) and P.M49L in the major allele. Kidney stones from two sibling patients were also observed though stereomicroscopic examination and scanning electron microscopy. Distinct morphological and inner-structure differences in calculi were noticed, suggesting clinical heterozygosity of PH1 to a certain extent. In brief, two novel missense mutations were identified probably in association with PH1, a finding which should provide an accurate tool for prenatal diagnosis, genetic counseling and screening for potential presymptomatic individuals.

Figure 1. Pedigree of the Chinese family with Primary hyperoxaluria type 1.

□, male; ○, female; ↗, proband.

Figure 2. CT scanning at different stages of three Chinese siblings of IIa, IIe and IIf with Primary Hyperoxaluria Type 1.

(A–C) CT scanning of bilateral kidneys of proband IIa; (D–H) CT scanning of bilateral kidneys of sibling IIe; (I) CT scanning of bilateral kidneys of sibling IIf.

Figure 3. Three AGXT mutations identified in the Chinese family with Primary Hyperoxaluria Type 1.

(A) wild type(left panel) and heterozygous mutant type (right panel) of p.M49L; (B) wild type(left panel) and heterozygous mutant type (right panel) of p.N72I; (C) wild type(left panel) and heterozygous mutant type (right panel) of p.R333*. Mutation naming and description rules refer to the latest guideline published by Human Genome Variation Society (http://www.hgvs.org/mutnomen/recs.html). AGXT-mRNA (NM_000030) starts from the first base of the first codon.

Figure 4. Morphologic characteristics of Calcium Oxalate Monohydrate stones from two Chinese siblings with Primary Hyperoxaluria Type 1.

Panels (A,B) show stone surfaces on stereomicroscopic examination (×10), and Panels (C,D) show the sections on scanning electron microscopy. The stones of both siblings had light-brown surfaces. Stones from sibling IIa showed irregular in shape, ununiformity in size, and inhomogeneous internal structures with the aggregations of various sizes and dimensions plate-like crystals (A,C); In contrast, the stones from IIf had smooth surface, regular shape, well-organized geometric cross sections with more compact and radiating inner structure (B,D).