A Novel Gene Is A Positional Candidate For Autosomal Recessive Polycystic Kidney Disease(ARPKD)

Department: Forensic Department, Medical College, Shantou UniversityAutosomal recessive polycystic kidney disease (ARPKD) is a common hereditary renal cystic disease in infants and children. The estimated incidence of ARPKD is widely variable, ranging from 1 in 6,000 to 1 in 55,000 live births. A morbidity of 1 in 20,000 was estimated by clinical geneticists. Approximately 1 out of 70 individuals is a carrier of an ARPKD mutant allele. By genetic linkage analyses, the gene responsible for this disease, termed polycystic kidney and hepatic disease 1 (PKHD1), was mapped on human chromosome 6p21.1-12, and has been further localized to a 1-cM genetic interval flanked by the D6S1714/D6S243 (telomeric) and D6S1024 (centromeric) markers. Recently, the disease interval was refined even further, to an ~840-kb genomic region. According to Celera database, there are two predicted genes, hCGl642636 and hCGl646861. Because a previous report demonstrated that the candidate gene for ARPKD may reside closer to the telomeric flanking marker (D6S1714) we focused our attention on hCG1646861.A fragment of RT-PCR product was amplified from primers based on the predicted hCG1646861 cDNA sequence, and used as aA Novel Gene is a Positional Candidate for Autosomal Recessive Polycystic Kidney Disease (ARPKD)Ph.D student: Huaqi XiongMentor : Prof. Xiaohu XuProf. Guanqing WuDepartment: Forensic Department, Medical College, Shantou UniversityAutosomal recessive polycystic kidney disease (ARPKD) is a common hereditary renal cystic disease in infants and children. The estimated incidence of ARPKD is widely variable, ranging from 1 in 6,000 to 1 in 55,000 live births. A morbidity of 1 in 20,000 was estimated by clinical geneticists. Approximately 1 out of 70 individuals is a carrier of an ARPKD mutant allele. By genetic linkage analyses, the gene responsible for this disease, termed polycystic kidney and hepatic disease 1 (PKHD1), was mapped on human chromosome 6p21.1-12, and has been further localized to a 1-cM genetic interval flanked by the D6S1714/D6S243 (telomeric) and D6S1024 (centromeric) markers. Recently, the disease interval was refined even further, to an ~840-kb genomic region. According to Celera database, there are two predicted genes, hCGl642636 and hCGl646861. Because a previous report demonstrated that the candidate gene for ARPKD may reside closer to the telomeric flanking marker (D6S1714) we focused our attention on hCG1646861.A fragment of RT-PCR product was amplified from primers based on the predicted hCG1646861 cDNA sequence, and used as aNorthern analyses demonstrated that the gene has discrete bands with one peak signals at -11-kb indicating PKHD1-T is likely to have multiple alternative transcripts, and PKHD1-T is highly expressed in adult and infant kidneys and weakly in the liver. This expression pattern parallels the tissue involvement observed in ARPKD. In-situ hybridization analysis further revealed that the expression of PKHD1-T in the kidney is mainly localized to the epithelial cells of collecting duct, the specific tubular segment involved in cyst formation in ARPKD. These features make it a strong positional candidate gene for ARPKD.For more understanding the function of PKHD1-T, we identified the homology gene in mice, called pkhdl, using RT-PCR and 5'RACE. The sequence is on chromosome 1, band A2-5 by FISH method same as we find on gene bank. The pkhdl encodes a 12225 bp transcript and is composed of 67 exons spanning an ~500-kb genomic region which longer than PKHD1-T and same as PKHD1-F. The ORF of PKHD1-T is 11994 bp long and is predicted to encode a 3398-amino-acid protein. The nucleotide of pkhdl is 76% identical and amino-acid is about 88% similar to human PKHDl.During the preparation of this publication, the gene responsible for ARPKD, PKHDl has been identified by other group, named as PKHDl-F. In comparison with their findings, we found that PKHDl-T is essentially identical to PKHDl. However, PKH...