MSc (Med)(Genetic Counselling), Faculty of Health Sciences, University of the Witwatersrand / Autosomal recessive polycystic kidney disease (ARPKD; MIM263200) is a severe recessively inherited disease of the kidneys and biliary tract, with an incidence of approximately 1 in 20000 in non-isolated populations. It has a variable clinical spectrum from neonatal demise (in 30-50%) to survival into adulthood. ARPKD is caused by mutations at a single locus, polycystic kidney and hepatic disease 1 (PKHD1), with over 270 pathogenic mutations described to date. The high rate of compound heterozygosity in affected individuals has made genotype-phenotype correlations difficult. A common missense mutation, p.M627K, in exon 20 of PKHD1 was identified previously on the majority of ARPKD disease associated alleles in the Afrikaans population of South Africa suggesting the presence of a founder effect. The aim of this study was to describe the clinical phenotype of ARPKD in Afrikaans speaking individuals found to be homozygous for the common mutation, and to compare this phenotype to previously described cohorts of patients with ARPKD, known to harbour a spectrum of mutations. This descriptive study used retrospective data collected from records of patients with ARPKD at Johannesburg and Pretoria Academic Hospitals. Twenty seven individuals from 24 families were included in the study. Marked clinical variability was demonstrated within this subject group supporting the limitation of genotype-phenotype correlation described worldwide. ARPKD was diagnosed at a median age of 27 days, older than a North American cohort (NAC) born after 1990 (median age of 1 day). The majority (93%) of subjects in this study were diagnosed with chronic renal v insufficiency (CRI) and hypertension (HT), indicating the renal morbidities to be more common than noted in previous studies, but occurring at a later median age (1.4 years vs 13.5 days in the NAC). This may indicate a trend toward milder expression of renal morbidities in the present study. Portal hypertension was also diagnosed more frequently (81%) than in previous studies but at a younger median age (1.3 years vs 2.8 years), although with similar complication rates. Overall statistical correlation was found between the renal and hepatic related morbidities in this study, indicating that progression of the condition is not organ specific. A survival rate of 89% at one year is comparable to previous studies with similar patient ascertainment. This cohort represents the largest series of patients affected by ARPKD with a common mutation, described to date. The findings will provide for more accurate, specific and informative genetic counselling in families with ARPKD and may present a resource for future studies of modifier genes and environmental influences on the phenotypic expression of ARPKD.

Autosomal recessive polycystic kidney disease (ARPKD) is a rare severe inherited disease manifested by cystic renal disease, congenital hepatic fibrosis and dilatatation of bile ducts. The spectrum of clinical manifestations is very wide and variable, depends on the age at which the disease was manifested. In severe forms of the disease, it is possible to detect the first symptoms prenatally around the 20th week of pregnancy due to increased echogenic kidneys and the presence of oligohydramnios. The causal gene of this disease is thePKHD1 gene with protein product fibrocystin that is most likely contributing on maintaining the intracellular concentration of Ca2+ cations. The exact phatophysiology mechanism of ARPKD remains unknown. Phenotypic manifestations of this disease may overlap with mutations associated with other genes. One of the genes mimicking the ARPKD phenotype is the HNF1B gene. Mutations associated with HNF1B gene are the most common monogenic cause of developmental kidney abnormalities. HNF1B is a tissue-specific transcription factor that regulates the expression of PKHD1. In experimental part I worked on genetic analysis of the HNF1B gene in 28 patients who have not been confirmed ARPKD diagnosis by detection of 2 PKHD1 mutations. For the purposes of mutational screening, I used...