The diagnosis and prognosis of autosomal dominant polycystic kidney disease

Cystic renal disease

Renal cysts are relatively common radiographic and clinical abnormalities. Cystic renal disease is a heterogeneous entity comprised of heritable, developmental, and acquired disorders. During the last decade, considerable progress has been made in reaching a consensus for standard terminologies and classifications of cystic renal disease among radiologists, pathologists, nephrologists, and urologists. This article discusses more common MR imaging-related types of cystic renal disease.

Characterization of microsatellite markers to diagnose ADPKD

Autosomal dominant polycystic kidney disease (ADPKD) maps to chromosome 16p13.3 (PKD1) and to chromosome 4q21-23 (PKD2), with the likelihood of a third unmapped locus. The size and genomic complexity of the PKD1 gene make it impractical to detect mutations for prenatal diagnosis. Therefore, pedigree-based linkage analysis remains useful for diagnosis of ADPKD. Since, the complete genome sequences of chromosome 16p13.3 and 4q21-23 including PKD1 and PKD2, respectively, were reported very recently, in order to do more precise diagnosis of ADPKD, we tried to find microsatellite markers. We performed database searches of 2000 kb of genome sequence across the 16p13.3 and the 4q21-23. To determine the distribution of alleles and the degree of polymorphism of the microsatellites, genotyping experiments were performed on 48 Korean individuals. We found novel 14 microsatellite markers around ADPKD that are more polymorphic and closer to PKD1 or PKD2 than the known markers. The novel microsatellite markers were applied to diagnose ADPKD families. These novel microsatellite markers are not only useful for presymptomatic and prenatal diagnosis of ADPKD, but also applicable in the study of positional cloning, human evolution and tumor biology.

Laparoscopic cyst decortication in autosomal dominant polycystic kidney disease: impact on pain, hypertension, and renal function

BACKGROUND AND PURPOSE

In patients with autosomal dominant polycystic kidney disease (ADPKD), laparoscopic cyst decortication (LCD) has been proposed as a means to relieve chronic cyst-related pain. We present our 7-year experience with LCD for ADPKD with regard to pain relief, hypertension, and renal function.

PATIENTS AND METHODS

Between August 1994 and February 2001, 29 ADPKD patients with chronic pain (N=29), hypertension (N=21), and renal insufficiency (N=10) underwent 35 LCD procedures. Every detectable cyst within 2 mm of the renal surface was treated. Pain relief was assessed using a pain analog scale; relative pain relief (RPR) equaled (preoperative pain score) - (postoperative pain score)/(preoperative pain score). Hypertension was evaluated using the antihypertensive therapeutic index (ATI): [(dose of blood pressure medication 1/max dose 1) + (dose med 2/max dose 2) + etc.] x 10. Renal function was assessed using the Cockcroft and Gault formula for creatinine clearance.

RESULTS

The mean operating room time was 4.9 hours (range 2.6-6.6 hours) with no conversions to open surgery. An average of 220 cysts (range 4-692) were treated per patient. The mean follow-up was 32.3 months (range 6-72 months). The RPR was 58%, 47%, and 63% at 12, 24, and 36 months, respectively. At 12, 24, and 36 months, 73%, 52%, and 81% of patients, respectively, noted >50% improvement in their pain compared with the preoperative situation. Five patients became normotensive, and patients improved their ATI by an average of 49% (range 11%-93%). However, six patients had worsening hypertension, with an ATI increase averaging 53% (range 11%-122%), and one patient who was not hypertensive preoperatively has since developed hypertension. The creatinine clearance changed +4%, +7%, and -2% at 12, 24, and 36 months, respectively. Only one patient had a >20% increase in creatinine clearance. The only patients with a >20% decrease in creatinine clearance were those who had a creatinine clearance <30 mg/dL preoperatively (average decrease 34% [range 20%-51%]).

CONCLUSIONS

For ADPKD patients with debilitating pain, extensive LCD can provide durable relief. In the majority of patients with pain and hypertension, a marked improvement in blood pressure also occurs. Cyst decortication was not associated with worsening renal function; indeed, renal function remained largely unchanged over the 3-year follow-up period.

Genotype-renal function correlation in type 2 autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common Mendelian disorder that affects approximately 1 in 1000 live births. Mutations of two genes, PKD1 and PKD2, account for the disease in approximately 80 to 85% and 10 to 15% of the cases, respectively. Significant interfamilial and intrafamilial renal disease variability in ADPKD has been well documented. Locus heterogeneity is a major determinant for interfamilial disease variability (i.e., patients from PKD1-linked families have a significantly earlier onset of ESRD compared with patients from PKD2-linked families). More recently, two studies have suggested that allelic heterogeneity might influence renal disease severity. The current study examined the genotype-renal function correlation in 461 affected individuals from 71 ADPKD families with known PKD2 mutations. Fifty different mutations were identified in these families, spanning between exon 1 and 14 of PKD2. Most (94%) of these mutations were predicted to be inactivating. The renal outcomes of these patients, including the age of onset of end-stage renal disease (ESRD) and chronic renal failure (CRF; defined as creatinine clearance < or = 50 ml/min, calculated using the Cockroft and Gault formula), were analyzed. Of all the affected individuals clinically assessed, 117 (25.4%) had ESRD, 47 (10.2%) died without ESRD, 65 (14.0%) had CRF, and 232 (50.3%) had neither CRF nor ESRD at the last follow-up. Female patients, compared with male patients, had a later mean age of onset of ESRD (76.0 [95% CI, 73.8 to 78.1] versus 68.1 [95% CI, 66.0 to 70.2] yr) and CRF (72.5 [95% CI, 70.1 to 74.9] versus 63.7 [95% CI, 61.4 to 66.0] yr). Linear regression and renal survival analyses revealed that the location of PKD2 mutations did not influence the age of onset of ESRD. However, patients with splice site mutations appeared to have milder renal disease compared with patients with other mutation types (P < 0.04 by log rank test; adjusted for the gender effect). Considerable renal disease variability was also found among affected individuals with the same PKD2 mutations. This variability can confound the determination of allelic effects and supports the notion that additional genetic and/or environmental factors may modulate the renal disease severity in ADPKD.

Cystic disease in women: clinical characteristics and medical management

Autosomal dominant polycystic kidney disease (ADPKD) is a dominantly inherited systemic disorder equally inherited in men and women characterized by renal cyst development and expansion ultimately leading to renal failure. ADPKD women have a slower rate of progression to renal failure, with a later age of entry into end-stage renal disease (ESRD) as compared with men. Renal cyst growth and renal expansion are the hallmarks of ADPKD, and women will develop renal insufficiency with smaller renal volume than their male counterparts. As well, women have different rates of occurrence of renal and extrarenal complications in ADPKD. Renal complications related to ADPKD, including hypertension and gross hematuria, occur more frequently in men than in women, whereas liver cystic disease occurs earlier and more frequently in women than in men. The presence of polycystic liver disease is related to pregnancy number and oral contraceptive pill use in ADPKD women. Importantly, massive polycystic liver disease requiring surgical intervention occurs primarily in ADPKD women. ADKPD women have a highly successful reproductive course. The chance of a successful pregnancy is excellent in ADPKD women and comparable to healthy unaffected women as long as prepregnancy blood pressure and renal function are normal. Fetal complication rates are no greater than in the general population; however, maternal complication rates in ADPKD women are high with an increased frequency of new or worsening hypertension as well as an increased occurrence of preeclampsia and preterm deliveries. Finally, increasing pregnancy number has minimal or no effect on renal outcome in ADPKD women.

Recent advances in the cell biology of polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a significant familial disorder, crossing multiple ethnicities as well as organ systems. The goal of understanding and, ultimately, curing ADPKD has fostered collaborative efforts among many laboratories, mustered on by the opportunity to probe fundamental cellular biology. Here we review what is known about ADPKD including well-accepted data such as the identification of the causative genes and the fact that PKD1 and PKD2 act in the same pathway, fairly well-accepted concepts such as the "two-hit hypothesis," and somewhat confusing information regarding polycystin-1 and -2 localization and protein interactions. Special attention is paid to the recently discovered role of the cilium in polycystic kidney disease and the model it suggests. Studying ADPKD is important, not only as an evaluation of a multisystem disorder that spans a lifetime, but as a testament to the achievements of modern biology and medicine.

Three novel mutations of the PKD1 gene in Korean patients with autosomal dominant polycystic kidney disease

Mutations at the PKD1 locus account for 85% of cases of the common genetic disorder called autosomal dominant polycystic kidney disease (ADPKD). Screening for mutations of the PKD1 gene is complicated by the genomic structure of the 5'-duplicated region encoding 75% of the gene. To date, more than 90 mutations of the PKD1 gene have been reported in the European and American populations, and relatively little information is available concerning the pattern of mutations present in the Asian populations. We looked for mutations of the PKD1 gene in 51 unrelated Korean ADPKD patients, using polymerase chain reaction (PCR) with primer pairs located in the 3' single-copy region of the PKD1 gene and by single-strand conformation polymorphism (SSCP) analysis. We found three novel mutations, a G to A substitution at nucleotide 11012 (G3601S), a C to A substitution at nucleotide 11312 (Q3701X), and a C to T substitution at nucleotide 12971 (P4254S), and a single polymorphism involving a G to C substitution at nucleotide 11470 (L3753L). These mutations were not found in control individuals, and no other mutations in the 3' single-copy region of the PKD1 gene of patients with these mutations were observed. In particular, P4254S segregated with the disease phenotype. The clinical data of affected individuals from this study, and of previously reported Korean PKD1 mutations, showed that patients with frameshift or nonsense mutations were more prone to develop end-stage renal failure than those with missense mutations. Our findings indicate that many different PKD1 mutations are likely to be responsible for ADPKD in the Korean population, as in the Western population.

Altered expression pattern of polycystin-2 in acute and chronic renal tubular diseases

Polycystin-2 represents one of so far two proteins found to be mutated in patients with autosomal-dominant polycystic kidney disease. Evidence obtained from experiments carried out in cell lines and with native kidney tissue strongly suggests that polycystin-2 is located in the endoplasmic reticulum. In the kidney, polycystin-2 is highly expressed in cells of the distal and connecting tubules, where it is located in the basal compartment. It is not known whether the expression of polycystin-2 in the kidney changes or whether it can be manipulated under certain instances. Therefore, the distribution of polycystin-2 under conditions leading to acute and chronic renal failure was analyzed. During ischemic acute renal failure, which affects primarily the S3 segment of the proximal tubule, a pronounced upregulation of polycystin-2 and a predominantly combined homogeneous and punctate cytoplasmic distribution in damaged cells was observed. After thallium-induced acute injury to thick ascending limb cells, polycystin-2 staining assumed a chicken wire-like pattern in damaged cells. In the (cy/+) rat, a model for autosomal-dominant polycystic kidney disease in which cysts originate predominantly from the proximal tubule, polycystin-2 immunoreactivity was lost in some distal tubules. In kidneys from (pcy/pcy) mice, a model for autosomal-recessive polycystic kidney disease in which cyst formation primarily affects distal tubules and collecting ducts, a minor portion of cyst-lining cells cease to express polycystin-2, whereas in the remaining cells, polycystin-2 is retained in their basal compartment. Data show that the expression and cellular distribution of polycystin-2 in different kinds of renal injuries depends on the type of damage and on the nephron-specific response to the injury. After ischemia, polycystin-2 may be upregulated by the injured cells to protect themselves. It is unlikely that polycystin-2 plays a role in cyst formation in the (cy/+) rat and in the (pcy/pcy) mouse.

Clinical and genetic epidemiology of inherited renal disease in Newfoundland

Clinical and genetic epidemiology of inherited renal disease in Newfoundland. Newfoundland's geography, settlement, and socioeconomic development have produced a population useful for the study of genetic diseases. This review examines the clinical and genetic epidemiologic studies of inherited renal diseases undertaken in this population in the past 15 years. Common founder effects and large families through each generation provided very extensive pedigrees with autosomal-dominant diseases, such as polycystic kidney disease (PKD) and von Hippel-Lindau disease. In the former disease the diagnostic utility of renal ultrasound was determined, as was the prognostic impact of genotype, the role of the renin-angiotensin system in the pre-hypertensive phase, the potential for somatic mutations of the PKD2 gene, or the combination of mutations in the PKD1 and PKD2 genes, in single cells to induce cysts, and the demonstration that human transheterozygotes of PKD1 and -2 are not embryonically lethal. The presence of multiple genetic isolates and the high coefficient of kinship have predisposed to autosomal recessive diseases such as Bardet-Biedl syndrome (BBS), autosomal-recessive PKD, primary hyperoxaluria, and dihydroxyadenine urolithiasis. We have reported the clinical manifestations and natural history of the BBS, with particular emphasis on the fact that renal abnormalities are cardinal manifestations of the disease, the presence of at least six different genotypes, the identity and function of the BBS6 gene, and the presence of three different BBS6 mutations. Because of its relatively homogenous origins and high coefficient of kinship, Newfoundland's population also may be useful for the study of complex diseases such as preeclampsia. Using unbiased ascertainment and strict diagnostic criteria, we have found a significant risk of preeclampsia and non-proteinuric gestational hypertension in sisters of probands with preeclampsia, particularly when probands are defined by severity of preeclampsia, an observation that supports a study to search for susceptibility genes. We conclude that collaborations between clinical epidemiologists and molecular geneticists, using the Newfoundland population, have provided important clinical and mechanistic insights into inherited renal diseases.

Mutation detection in the duplicated region of the polycystic kidney disease 1 (PKD1) gene in PKD1-linked Australian families

Screening for disease-causing mutations in the duplicated region of the PKD1 gene was performed in 17 unrelated Australian individuals with PKD1-linked autosomal dominant polycystic kidney disease. Exons 2-21 and 23-34 were assayed using PKD1-specific PCR amplification and direct sequencing. We have identified 12 novel probably pathogenic DNA variants, including five truncating mutations (Q563X, c.5105delAT, c.5159delG, S2269X, c.9847delC), two in-frame deletions (c.7472del3, c.9292del39), and two splice-site mutations (IVS14+1G>C, IVS16+1G>T). Three of the mutations (G381C, Y2185D, G2785D) were predicted to lead to the replacement of conserved amino acid residues, with ensuing changes in protein conformation. Defects in the duplicated region of PKD1 thus account for 63% of our patients. Together with the previously detected mutations (Q4041X, R4227P) in the 3 region of the gene, the study has achieved an overall mutation detection rate of 74%. In addition, we have detected 31 variants (nine novel and 22 previously published) that did not segregate with the disease and were considered to be neutral polymorphisms. Three of the nine novel polymorphisms were missense mutations with a predicted effect on protein conformation, emphasizing the problems of interpretation in PKD1 mutation screening.

Mutations of the human polycystic kidney disease 2 (PKD2) gene

Autosomal dominant polycystic kidney disease (ADPKD) is an inherited nephropathy, usually of late onset (onset between third to seventh decade), primarily characterized by the formation of fluid-filled cysts in the kidneys. It is one of the most frequent inherited conditions affecting approximately 1:1,000 Caucasians. Two major genes have been identified and characterized in detail: PKD1 and PKD2, mapping on chromosomes 16p13.3 and 4q21-23, respectively. A third gene, PKD3, has been implicated in selected families. Polycystic kidney disease of types 1 or 2 follows a very similar course of symptoms, both being multisystem pleiotropic disorders of indistinguishable picture on clinical grounds. The only difference is that patients with PKD2 mutations run a milder course compared to PKD1 carriers, with an average 10-20 years later age of onset and lower probability to reach end-stage-renal failure. The proteins polycystin-1 and -2 are trans-membranous glycoproteins hypothesized to participate in a common signaling pathway, interacting with each other and with other proteins, and coordinately expressed in normal and cystic tissue. Renal cysts most probably arise after a second somatic event, which inactivates the inherited healthy allele of the same gene, or perhaps one of the alleles of the other gene counterpart, generating a trans-heterozygous state. This article reviews the reported mutations in PKD2. Mutations of all kinds have been reported over the entire sequence of the PKD2 gene, with no apparent significant clustering and with some evidence of genotype/phenotype correlation. Most families harbor their own private mutations but a few recurrent events have been reported in unrelated families.

Updates in nephrology. A summary of common diagnoses encountered in the clinical practice

This article includes a review of hypertension, nephrolithiasis and cystic diseases of the kidney, all quite common diagnoses. These days, as concerns are growing, some are considering diabetes mellitus to be a national epidemic. Thus, our entire article focuses on the diabetic renal disease. The current approach to the diagnosis and treatment of acute renal failure and chronic renal insufficiency is discussed, including treatment modalities such as dialysis and transplantation. This article is not at all intended to be a comprehensive review of each topic included, but rather it is an attempt to make the reader more familiar with the fascinating and continuously evolving field of nephrology.

Impaired endocytosis may represent an obstacle to gene therapy in polycystic kidney disease

BACKGROUND

Autosomal-dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease and a frequent cause of chronic renal failure. The cloning of the PKD1 and PKD2 genes, which are mutated in the great majority of patients with this disease, opens up the opportunity for somatic gene therapy by introduction of the wild-type gene or cDNA. Several publications have provided evidence, that many portions of the nephron and the collecting duct can form cysts, including the proximal tubule. Alterations in the proximal tubule may prevent the efficient endocytosis of filtered proteins and thus contribute to proteinuria, a frequent symptom in patients with polycystic kidney disease. At the same time this may also negatively affect various gene therapy strategies, since endocytosis is important for the uptake of foreign DNA at least under some circumstances. In the (cy/+) rat, a widely used animal model for ADPKD, cysts almost exclusively develop from proximal tubules, and we have therefore investigated whether proteinuria and defective endocytosis also occur in this model.

METHODS

Proteinuria was demonstrated by direct measurement and by protein gel electrophoresis of urines from 16 week-old (cy/+) rats. Endocytosis was investigated by injection of FITC-dextran and immunohistochemical staining with anti-ClC-5 and anti-megalin antibodies.

RESULTS

Similar to the observations made in ADPKD patients, proteinuria also develops in the (cy/+) rat. Using FITC-labeled dextran as an in vivo tracer for renal tubular endosomal function, we could show that portions of cyst-lining epithelia from proximal tubules have lost the ability to endocytose, which is necessary for the reabsorption of albumin and lower-molecular-weight proteins. By immunohistochemistry the expression of other proteins implicated in endocytosis, such as the chloride channel ClC-5 and the albumin receptor megalin, correlated well with the presence and absence of FITC-dextran in cyst wall epithelia.

CONCLUSION

These data indicate that proteinuria and albuminuria in the (cy/+) rat model for ADPKD are due to a loss of the endocytic machinery in epithelia of proximal tubular cysts. Such a defect may also reduce the efficacy of certain gene therapy protocols.

Bilateral hand-assisted laparoscopic nephrectomy for autosomal dominant polycystic kidney disease using a single midline HandPort incision

OBJECTIVES

To present one of the first known series of bilateral, transperitoneal laparoscopic nephrectomy for autosomal dominant polycystic kidney disease using a hand-assisted technique by way of a single, midline HandPort incision. Synchronous, bilateral nephrectomy for autosomal dominant polycystic kidney disease is an infrequently performed procedure, with only a few reports using laparoscopy.

METHODS

We retrospectively reviewed the charts of 4 patients undergoing bilateral hand-assisted laparoscopic nephrectomy for symptomatic autosomal dominant polycystic kidney disease between June 2000 and January 2001. Follow-up consisted of chart review and telephone survey.

RESULTS

All 4 patients underwent successful bilateral hand-assisted laparoscopic nephrectomy, with a mean operative time of 286 minutes. This included 1 patient who underwent simultaneous laparoscopic marsupialization of symptomatic hepatic cysts. The average size of the polycystic kidneys removed was 1582 g. Complications included acute tubular necrosis of a renal allograft in 1 patient that resolved spontaneously and retained retroperitoneal cystic fluid that required percutaneous drainage in another patient. All patients did well postoperatively, with complete resolution of their presenting symptoms. Those with renal allografts had stable function at the last follow-up visit.

CONCLUSIONS

Bilateral hand-assisted laparoscopic nephrectomy using a single HandPort incision is a feasible alternative for the removal of symptomatic polycystic kidneys. It offers the advantage of easier identification and control of hilar structures that are often obscured by the distorted renal anatomy. In addition, it allows the simultaneous performance of other intra-abdominal procedures.

Genetic heterogeneity in Korean families with autosomal-dominant polycystic kidney disease (ADPKD): the first Asian report

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is the most common hereditary renal disease in adults, and the prevalence of this disease within the chronic haemodialysis patient population is known to be approximately 2% in Korea. So far, three genetic locus have been identified as being responsible for ADPKD, and approximately 85% of the cases in Western countries are related to the PKD1 gene. However, little information is available concerning the pattern of linkage analysis in Asian populations.

METHODS

48 families with hereditary renal cysts were recruited by consent and their molecular genetic characteristics were studied. Linkage analysis was done with microsatellite markers (PKD1: SM7, UT581, AC2.5, KG8, D16S418; PKD2: D4S423, D4S1534, D4S1542, D4S1544, D4S2460). Genomic DNA polymerase chain reaction (PCR) and polyacrylamide gel electrophoresis (PAGE) gel run were performed, and the resultant allele patterns were compared with sonographic findings.

RESULTS

The results of this study showed that the ratio PKD1:PKD2 was 31:8, and that the PKD2 families exhibited a tendency toward a milder renal prognosis than the PKD1 families.

CONCLUSION

We confirmed the applicability of linkage analysis for ADPKD in the Korean population, and our data confirmed a similar incidence of PKD1 (79%) and PKD2 (21%) in Korean patients as in the Western population.

Laparoscopic cyst marsupialization in patients with autosomal dominant polycystic kidney disease

PURPOSE

Autosomal dominant polycystic kidney disease is characterized by progressively enlarging renal cysts associated with hypertension, renal failure, pain, hematuria and infection. We explored the role of laparoscopic cyst marsupialization for managing cyst related problems.

MATERIALS AND METHODS

In 4 male and 11 female adults with autosomal dominant polycystic kidney disease who had preserved renal function laparoscopic cyst marsupialization was done for pain unilaterally and bilaterally in 9 and 6, respectively. An average of 204 cysts per kidney (range 11 to 635) were decorticated or drained.

RESULTS

Average operative time was 5.5 hours. Patients were discharged from the hospital after an average of 3.2 days. At a mean followup of 2.2 years (range 0.5 to 5) pain was decreased an average of 62% (range 30% to 90%) in 11 cases (73%). One patient had no improvement and 1 had subsequent worsening of pain postoperatively. Two patients with initial improvement had pain recurrence 4 and 36 months postoperatively, respectively. Hypertension resolved in 1 patient (7%), improved in 20% and did not change in 40%. In 33% of the cases hypertension worsened, requiring additional antihypertensive medication. Renal function remained stable in 13 patients (87%), improved in 1 (6.5%) and worsened in 1 (6.5%). Overall patients who underwent a bilateral procedure had better long-term pain relief and more improvement in hypertension.

CONCLUSIONS

Laparoscopic cyst marsupialization may effectively decrease cyst associated pain. In some cases hypertension may be improved. Renal function remained stable in all except 1 patient. At a mean followup of 2.2 years the benefits of aggressive laparoscopic cyst decortication appear to be relatively long lasting when bilateral decortication is indicated. The benefits of unilateral cyst decortication are less predictable and of shorter duration.

Individual Renal Function in Polycystic Kidney Disease

PURPOSE

This study was undertaken to determine individual renal function in patients with autosomal dominant polycystic kidney disease (ADPKD).

MATERIALS AND METHODS

The authors initially examined (study t1) 25 patients with ADPKD (12 female, 13 male; ages 18 to 68 years). The serum creatinine concentration and glomerular filtration rate, measured by Tc-99m DTPA, were 1.5 +/- 0.56 mg/dl and 65.7 +/- 31 ml.minute-1.1.73 m2, respectively. Thirteen patients had a follow-up study (t2) 2 years after their initial evaluations. Individual renal function was assessed on Tc-99m DMSA renal scans.

RESULTS

The mean (+/- SD) difference between left kidney DMSA (DMSA-L) and right kidney DMSA (DMSA-R) was 7.04 % +/- 16.48%. In 20 patients (80%), the left kidney had a lower percentage contribution to the total renal function compared with the right kidney. When the results of the two studies were compared, deterioration in renal function was noted. In the t1 study, the mean serum creatinine concentration and glomerular filtration rate were 1.7 mg/dl and 67.02 ml.minute-1.1.73 m2 respectively, and in the t2 study these values were 2.01 mg/dl and 57.15 ml.minute-1.1.73 m2, respectively. No difference, however, was found in individual renal function in the two studies.

CONCLUSIONS

In patients with ADPKD, the percentage contribution of each kidney to total renal function is not equal and remains stable during the progression of renal failure.

Laparoscopic bilateral synchronous nephrectomy for autosomal dominant polycystic kidney disease: the initial experience

PURPOSE

We report our experience with laparoscopic bilateral synchronous nephrectomy for giant symptomatic autosomal dominant polycystic kidney disease (ADPKD) and compare outcome data with open bilateral nephrectomy.

MATERIALS AND METHODS

Since March 1998, 10 patients underwent bilateral synchronous laparoscopic nephrectomy for giant symptomatic ADPKD. A 3 port retroperitoneal laparoscopic approach was used to secure the renal hilum and mobilize the kidney. Intact specimen extraction was performed through a midline infraumbilical extraperitoneal incision. The patient was then repositioned for the contralateral retroperitoneoscopic nephrectomy, with the second specimen also delivered through the same infraumbilical incision. Data were retrospectively compared with 10 patients who had undergone bilateral synchronous open nephrectomy for ADPKD between 1981 and 1992.

RESULTS

Patients in the laparoscopic and open groups were comparable in regard to age (53 versus 47 years, p = 0.54) and Anesthesiologist Society of America class (3 versus 3, p = 0.84) but patients in the laparoscopic group were significantly more obese (body mass index 35.9 versus 23.8, p = 0.02). For comparable total specimen weights (3 versus 3 kg, p = 0.69) surgical time was longer in the laparoscopic group (4.4 versus 3.8 hours, p = 0.007). However, the laparoscopic group was superior in regard to blood loss (150 versus 325 cc, p = 0.05), postoperative requirement of nasogastric tube (10% versus 100%, p = 0.0001), narcotic analgesics (34.2 versus 120.4 mg. morphine sulfate equivalent, p = 0.03) and hospital stay (1.5 versus 9 days, p = 0.004). Complications occurred in 5 patients (50%) in the laparoscopic group and 4 (40%) in the open group (p = 0.66). No laparoscopic case was converted to open surgery.

CONCLUSIONS

Synchronous bilateral retroperitoneal laparoscopic nephrectomy for giant symptomatic adult polycystic kidney disease is feasible, safe and efficacious, and can be performed either before or after renal transplantation. Compared to open surgery, the laparoscopic approach results in significantly shorter hospital stay, decreased morbidity and quicker recovery. Laparoscopy is currently our technique of choice in this setting.

A "two-hit" model of cystogenesis in autosomal dominant polycystic kidney disease?

An intriguing feature of autosomal dominant polycystic kidney disease (ADPKD) is the focal and sporadic nature of individual cyst formation. Typically, only a few renal cysts are detectable in an affected individual during the first two decades of life. By the fifth decade, however, hundreds to thousands of renal cysts can be found in most patients. Additionally, significant intra-familial variability of ADPKD has been well documented. Taken together, these findings suggest that factor(s) in addition to the germline mutation of a polycystic kidney disease gene might be required for individual cyst formation. Indeed, recent studies have provided compelling evidence in support of a "two-hit" model of cystogenesis in ADPKD. In this model, inactivation of both copies of a polycystic kidney disease gene by germline and somatic mutations within an epithelial cell provides growth advantages for it to proliferate clonally into a cyst. This article highlights key findings of these recent studies and discusses the controversies and implications of the "two-hit" model in ADPKD.

Liver transplantation for polycystic liver disease

Polycystic liver disease (PLD) may provoke massive hepatomegaly and severe physical and social handicaps. Data on orthotopic liver transplantation (OLT) for PLD are rare and conflicting. Conservative surgery (resection or fenestration) is indicated for large single cysts, but its value for small diffuse cysts is questionable. In addition, conservative surgery is not devoid of morbidity and mortality. OLT offers the prospect of a fully curative treatment, but controversy remains because those patients usually have preserved liver function. Thus, we reviewed our experience with OLT for PLD. Sixteen adult women underwent OLT for small diffuse PLD between 1990 and 1999. Mean age was 45 years (range, 34 to 56 years). Fourteen patients had combined liver and kidney cystic disease, but only 1 patient required combined liver and kidney transplantation, whereas 13 patients underwent OLT alone. Two patients had isolated PLD. Indications for transplantation were massive hepatomegaly causing physical handicaps (n = 16), social handicaps (n = 16), malnutrition (n = 4), and cholestasis and/or portal hypertension (n = 5). OLT caused no technical difficulty in 15 of 16 patients (surgery duration, 6.8 hours; range, 5 to 8 hours), with blood transfusions of 7.9 units (range, 0 to 22 units). One patient who underwent attempted liver-mass reduction pre-OLT died of bleeding and pulmonary emboli. Native liver weight was 10 to 20 kg. Posttransplantation immunosuppression consisted of cyclosporine or FK506, azathioprine, and steroids (discontinued at 3 months). Morbidity included biliary stricture (2 patients), revision for bleeding and hepatitis (1 patient), pneumothorax and subphrenic collection (1 patient), and tracheostomy (1 patient). One patient died of lung cancer 6 years posttransplantation. Both patient and graft survival rates are 87.5% (follow-up, 3 months to 9 years). Of 15 patients who underwent OLT alone, only 1 patient needed a kidney transplant 4 years after OLT. Kidney function has remained satisfactory in the other patients despite the use of cyclosporine or FK506 (last follow-up creatinine level, 1.55 mg/dL; range, 0.80 to 2.85 mg/dL). OLT had a dramatic impact on daily quality of life, enabling these patients to go back to a fully active life style. OLT offers the chance of a definitive treatment in patients with extensive, small, diffuse PLD that has evolved into severely handicapping hepatomegaly. In contrast to previous studies, combined liver and kidney transplantation is rarely needed. Patient symptoms and chances of definitive palliation offered by OLT must be balanced against the risks of transplantation and lifelong commitment to immunosuppression.

A possible role for metalloproteinases in renal cyst development

The expansion of cysts in polycystic kidneys bears several similarities to the invasion of the extracellular matrix by benign tumors. We therefore hypothesized that cyst-lining epithelial cells produce extracellular matrix-degrading metalloproteinases and that the inhibition of these enzymes may represent a potential target for therapeutic intervention. Using in situ hybridization, we first analyzed the expression of membrane-type metalloproteinase 1 (MMP-14), an essential matrix metalloproteinase, of its inhibitor TIMP-2, and of the cytokine transforming growth factor (TGF)-beta2 in the (cy/+) rat model of autosomal-dominant polycystic kidney disease. Upregulated MMP-14 mRNA was predominantly located in cyst-lining epithelia and distal tubules, whereas TIMP-2 mRNA was confined almost exclusively to fibroblasts. TGF-beta2, a cytokine known to regulate the expression of matrix metalloproteinases and their inhibitors, was also expressed by cyst wall epithelia. We then treated (cy/+) rats with the metalloproteinase inhibitor batimastat for a period of 8 wk. The treatment with the metalloproteinase inhibitor batimastat resulted in a significant reduction of cyst number and kidney weight. Our study suggests that metalloproteinase inhibitors represent a new therapeutic tool against polycystic kidney disease, which should be applicable independently of the background of the disease.

Assessment of renal function with color Doppler ultrasound in autosomal dominant polycystic kidney disease

BACKGROUND

Measurement of renal blood flow by color Doppler ultrasound is useful for assessment of renal function in a variety of renal disorders. In autosomal dominant polycystic kidney disease (ADPKD), however, it might be difficult to visualize interlobar arteries because of deformity of renal structure. To evaluate the usefulness of color Doppler in ADPKD, parameters determined by blood flow examination were compared with the results of ordinal renal function tests.

METHODS

Twenty-one patients with ADPKD were examined by color Doppler ultrasound measurement. In each patient, 10 interlobar arteries in both kidneys were investigated. Minimum blood flow velocity (Vmin), maximum blood flow velocity (Vmax), mean blood flow velocity (Vmean), acceleration, resistive index and pulsatility index were measured in relation to the results of creatinine clearance, serum creatinine, blood urea nitrogen and 15 and 120 min values of the phenolsulfonphthalein test.

RESULTS

In all patients, interlobar arteries were able to be visualized and blood-flow profile was measured. Although variations of Vmin, Vmax, Vmean and acceleration were relatively large, the resistive index and pulsatility index varied little in each kidney. Mean values of Vmin (P < 0.005), Vmean (P < 0.05), resistive index (P < 0.005) and pulsatility index (P < 0.005) were well correlated to creatinine clearance with statistical significance.

CONCLUSIONS

In ADPKD, color Doppler ultrasound measurement is a useful method for assessment of renal function and could be used for monitoring the dynamic state of renal blood flow as a non-invasive technique.

Lack of association of ACE/angiotensinogen genotype with renal function in autosomal dominant polycystic kidney disease

ACE polymorphisms have recently been shown to associate with worse renal and or cardiovascular outcome, with the D allele widely reported as a risk factor for cardiovascular disease. In autosomal dominant polycystic kidney disease (ADPKD), there are conflicting reports of an association between ACE polymorphisms and disease phenotype. There are no previous reports of any association between angiotensinogen polymorphisms and clinical phenotype in ADPKD. We examined the ACE I/D and angiotensinogen M235T polymorphisms in 176 patients with ADPKD. Patients are categorized into three groups according to the reason for initial investigation. Clinical history and examination findings were recorded at the time of first referral. A cohort of 17 patients had progressive renal impairment observed after 3 or more years of follow-up. Reciprocal creatinine against time was plotted in this group. From the patient population of 176, a total of 33 patients reached end-stage renal failure (ESRF) or a serum creatinine greater than 500 microm/liter. ACE genotype and M235T polymorphism frequencies were compared across groups. Serum creatinine and presence of hypertension and onset of ESRF were taken as outcome variables; age and source of referral were taken as confounding variables. There was no association of any genotype or allele with either creatinine, inverse creatinine, hypertension, or age at end-stage renal failure. These findings do not support the proposition that ACE genotype or angiotensinogen polymorphisms are associated with a worse prognosis in patients with ADPKD.

Bilineal disease and trans-heterozygotes in autosomal dominant polycystic kidney disease

In searching for a putative third gene for autosomal dominant polycystic kidney disease (ADPKD), we studied the genetic inheritance of a large family (NFL10) previously excluded from linkage to both the PKD1 locus and the PKD2 locus. We screened 48 members of the NFL10 pedigree, by ultrasonography, and genotyped them, with informative markers, at both the PKD1 locus and the PKD2 locus. Twenty-eight of 48 individuals assessed were affected with ADPKD. Inspection of the haplotypes of these individuals suggested the possibility of bilineal disease from independently segregating PKD1 and PKD2 mutations. Using single-stranded conformational analysis, we screened for and found a PKD2 mutation (i.e., 2152delA; L736X) in 12 affected pedigree members. Additionally, when the disease status of these individuals was coded as "unknown" in linkage analysis, we also found, with markers at the PKD1 locus, significant LOD scores (i.e., >3.0). These findings strongly support the presence of a PKD1 mutation in 15 other affected pedigree members, who lack the PKD2 mutation. Two additional affected individuals had trans-heterozygous mutations involving both genes, and they had renal disease that was more severe than that in affected individuals who had either mutation alone. This is the first documentation of bilineal disease in ADPKD. In humans, trans-heterozygous mutations involving both PKD1 and PKD2 are not necessarily embryonically lethal. However, the disease associated with the presence of both mutations appears to be more severe than the disease associated with either mutation alone. The presence of bilineal disease as a confounder needs to be considered seriously in the search for the elusive PKD3 locus.

Effect of ACE gene polymorphism on age at renal death in polycystic kidney disease in Japan

Polycystic kidney disease (PKD) is one of the most common genetic disorders and a major cause of renal death or end-stage renal disease (ESRD) requiring regular hemodialysis. The responsible genes recently have been cloned; however, genetic factors influencing the rate of progression to ESRD in patients with PKD have yet to be defined. Several studies have shown increased activity of the renin-angiotensin system (RAS) in patients with PKD. In addition, genetic polymorphisms of the RAS have been associated with the development of cardiovascular diseases. Therefore, these polymorphisms are good candidates for disease-modifying genetic factors or markers in PKD. In two previous reports of white subjects with a cumulative survival analysis, it was suggested that patients with P:KD1 homozygous for the deletion allele of the angiotensin-converting enzyme (ACE) gene are at increased risk for early renal death. To confirm this hypothesis in Japanese subjects, 103 individuals with PKD were genotyped for several components of the RAS, ie, ACE insertion/deletion (I/D) polymorphism, angiotensinogen (AGT) M235T, and angiotensin II type 1 receptor (AT1) A1166C. Seventy-six of the 103 patients (73.8%) reached ESRD at an average age of 52.1 +/- 11.3 years. The frequencies of each genotype of the genes were similar to those expected from Hardy-Weinberg equilibrium. There was a tendency to an excess of patients homozygous for the D allele in patients with ESRD (DD in patients with ESRD, 11.8%; DD in patients without ESRD, 3.7%; chi-square, 1.505; P: = 0.22). Cumulative renal survival was significantly less in those with the DD genotype compared with ID/II genotypes. Estimated mean renal survival was 46.4 years (95% confidence interval, 39.5 to 53.3) in subjects with the DD genotype and 57.2 years (95% confidence interval, 54.2 to 60.2) in ID/II genotypes (chi-square, 7.76; P: = 0.0053). There was no association between age at onset of ESRD and either M235T or A1166C polymorphism. These findings suggest that Japanese patients with PKD homozygous for the D allele of the ACE gene are at increased risk for developing ESRD at an early age.

Approach to decortication of simple cysts and polycystic kidneys

Laparoscopic excision and marsupialization of symptomatic of recurrent simple renal cysts is an alternative to open or percutaneous surgery. Such surgery may also be useful for pain relief in patients with autosomal dominant polycystic kidney disease (ADPKD). An occlusion balloon catheter is placed in the renal pelvis at the start of the procedure. Cysts are punctured, and the outer wall of the larger cysts is excised with care not to incise the renal parenchyma. In patients with ADPKD, it is important to mobilize the kidney completely, particularly the upper pole, to treat every visible cyst. A laparoscopic ultrasound probe is used to guide the unroofing of any large cysts within 5 to 10 mm of the renal surface. At the end of the procedure, the integrity of the collecting system is confirmed. Strict criteria must be used in selecting patients with simple cysts for laparoscopic marsupialization to minimize the incidence of unsuspected malignancy, and the cyst wall should be examined by frozen and permanent section. Long-term follow-up is needed to evaluate the effect of laparoscopic decompression in ADPKD.

Screening the 3' region of the polycystic kidney disease 1 (PKD1) gene in 41 Bulgarian and Australian kindreds reveals a prevalence of protein truncating mutations

Screening for disease-causing mutations in the unique region of the polycystic kidney disease 1 (PKD1) gene was performed in 41 unrelated individuals with autosomal dominant polycystic kidney disease. Exons 34-41 and 43-46 were assayed using PCR amplification and SSCP analysis followed by direct sequencing of amplicons presenting variant SSCP patterns. We have identified seven disease-causing mutations of which five are novel [c.10634-10656del; c.11587delG; IVS37-10C>A; c.11669-11674del; c.13069-13070ins39] and two have been reported previously [Q4010X; Q4041X]. Defects in this part of the gene thus account for 17% of our group of patients. Five of the seven sequence alterations detected are protein-truncating which is in agreement with mutation screening data for this part of the gene by other groups. The two other mutations are in-frame deletions or insertions which could destroy important functional properties of polycystin 1. These findings suggest that the first step toward cyst formation in PKD1 patients is the loss of one functional copy of polycystin 1, which indirectly supports the "two-hit" model of cystogenesis where a second somatic mutation inactivating the normal allele is necessary to occur for development of the disease condition.

Estimating prevalence in single-gene kidney diseases progressing to renal failure

Incidence and prevalence, the measures of "frequency, " are often confused. While in a nonhereditary situation, the useful parameter is the incidence rate, evaluating the impact of an etiologic factor, it is prevalence that is considered useful in a hereditary disease. Prevalence may concern either the whole population or a fraction of this population, that is, males or females or individuals at a given age, for example, at birth. Pathologic phenotype and morbid genotype prevalences have to be clearly differentiated. In this article, we review the epidemiologic surveys allowing an estimation of the distribution of major single-gene kidney diseases progressing to renal failure in different populations. In order to compare their results, the geographic/ethnic composition of the population, the determination of its size, the choice and mode of calculation of the epidemiologic measure, the definition of the disease and modes of diagnosis, the inclusion of cases, the sources of ascertainment and the possible causes of underascertainment, and the period of time during which events were counted should be analyzed accurately. Although their impact in terms of morbidity, hospitalizations, mortality, and cost to society is high, this review shows that information on the prevalence of single-gene kidney diseases is far from complete. To date, the data essentially apply to large populations of European origin. A part of the variation among prevalence data may be due to methodological differences. Not representative are the small populations in which some rare diseases, especially recessive, are found with a high prevalence.

Volumetric measurement of renal cysts and parenchyma using MRI: phantoms and patients with polycystic kidney disease

We have developed an MR method to measure the volumes of renal cysts and parenchyma in patients with polycystic kidney disease. Phantoms were designed to simulate polycystic kidneys. Four patients were recruited. MR scans were performed on the phantoms and patients. A stereology technique was applied for image segmentation and volume measurement. Volumetric measurement of renal cysts and parenchyma was accurate in phantom studies and reliable in both phantom and patient studies in these limited examples.

Laparoscopic nephrectomy in patients with end-stage renal disease and autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is often characterized by end-stage renal disease (ESRD) and problems including pain, hematuria, and infection. Open nephrectomy is curative; however, the morbidity of the procedure is considerable. Between 1995 and 1998, 11 laparoscopic nephrectomies were performed on nine symptomatic patients (five men and four women) with ESRD and ADPKD. Two patients underwent a staged bilateral laparoscopic nephrectomy. All patients presented with abdominal or flank pain and an abdominal mass. Other clinical problems included hypertension in eight patients, urinary tract infections in two patients, and gross hematuria in one patient. Seven patients were receiving long-term dialysis treatment, and two patients had undergone prior renal transplantation. Patients were evaluated for preoperative and postoperative pain, analgesic use, hospital course, and convalescence. The overall average operative time was 6.3 hours, with an average estimated blood loss of 153 mL. Eight nephrectomy specimens were removed by morcellation, and three specimens were removed intact through a 7- to 12-cm incision. The average hospital stay was 3 days, and the average time to normal activity was 5 weeks. With a mean follow-up of 31 months, all nine patients reported elimination of their preoperative pain based on a pain analogue score. Six major and two minor complications occurred, including blood transfusion, a vena cavotomy, splenic cyanosis, pulmonary embolism, clotted arteriovenous fistula, and brachial plexus injury. Incisional hernias occurred in two of the three patients who underwent open removal. One patient noted improvement, and two patients noted resolution of their hypertension postoperatively. Laparoscopic nephrectomy in patients with ADPKD and ESRD offers an effective alternative to open nephrectomy to manage renal-related pain. This procedure provides the benefits of minimal intraoperative blood loss, minimal postoperative pain, brief hospital stay, and rapid convalescence.

A novel frameshift mutation (2436insT) produces an immediate stop codon in the autosomal dominant polycystic kidney disease 2 (PKD2) gene

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a genetically heterogeneous disorder that can be caused by mutations in at least three different genes. Several mutations have been identified in PKD1 and PKD2 genes. Most of the mutations found in PKD2 gene are predicted to cause premature termination of the protein.

METHODS

We analysed an Argentinian family characterized previously as PKD2. The PKD2 gene was amplified from genomic DNA using 17 primer pairs and the products were analysed by heteroduplex analysis. PCR products that showed a variation by heteroduplex analysis were sequenced directly. The mutation was confirmed by sequencing relatives. The segregation of the mutation in this family was verified by restriction endonuclease digestion of PCR products obtained from genomic DNA of all family members. Results and conclusions. Here, we report a novel mutation present in an Argentinian family characterized as PKD2 by linkage analysis. The mutation, shared by all affected members of the family, is a thymidine insertion at position 2436 of the gene, which results in a translation frameshift and creates an immediate stop codon. This mutation is expected to lead to a truncated protein that lacks the interacting domain with the PKD1 gene product. The thymidine insertion abolished a Ddel restriction site, allowing a rapid test for detection of PKD2 carriers in the family.

Autosomal dominant polycystic kidney disease-type 2. Ultrasound, genetic and clinical correlations

BACKGROUND

Ultrasound, genetic and clinical correlations are available for ADPKD-1, but lacking for ADPKD-2. The present study was carried out to address: (i) the age-related diagnostic usefulness of ultrasound compared with genetic linkage studies; (ii) the age-related incidence and prevalence of relevant symptoms and complications; and (iii) the age and causes of death in patients with ADPKD-2.

METHODS

Two hundred and eleven alive subjects, from three ADPKD-2 families at 50% risk, were evaluated by physical examination, consultation of hospital records, biochemical parameters, ultrasound and with genetic linkage and DNA mutation analyses. Nineteen deceased and affected family members were also included in the study.

RESULTS

Of the 211 alive members, DNA linkage studies and direct mutation analyses showed that 106 were affected and 105 were not. Ultrasound indicated 94 affected, 108 not affected and nine equivocal results in nine children under the age of 15. For all ages, the false-positive diagnostic rate for ultrasound was 7.5% and the false-negative rate was 12.9%. The difference between ultrasound and DNA findings was most evident in children aged 5-14 years where the ultrasound was correct in only 50% and wrong or inconclusive in the remaining 50%. The mean age of the 106 alive, ADPKD-2 genetically affected patients was 37.9 years (range: 6-66 years). Among them, 23.5% had experienced episodes of renal pain, 22.6% were treated for hypertension, 22.6% had experienced at least one urinary tract infection, 19.8% had nephrolithiasis, 11.3% had at least one episode of haematuria, 9.4% had asymptomatic liver cysts, 7.5% had developed chronic renal failure and 0.9% had reached end-stage renal failure. Of the 19 deceased members, nine died before reaching end-stage renal failure at a mean age of 58.7 years (range: 40-68 years), mainly due to vascular complications, while the remaining 10 died on haemodialysis at a mean age of 71.4 years (range: 66-82 years).

CONCLUSIONS

DNA analysis is the gold standard for the diagnosis of ADPKD-2, especially in young people. Ultrasound diagnosis is highly dependent on age. Under the age of 14, ultrasound is not recommended as a routine diagnostic procedure, but ultrasound becomes 100% reliable in excluding ADPKD-2 in family members at 50% risk, over the age of 30. ADPKD-2 represents a mild variant of polycystic kidney disease with a low prevalence of symptoms and a late onset of end-stage renal failure.

Molecular genetics and mechanism of autosomal dominant polycystic kidney disease

Considerable progress toward understanding pathogenesis of autosomal dominant polycystic disease (ADPKD) has been made during the past 15 years. ADPKD is a heterogeneous human disease resulting from mutations in either of two genes, PKD1 and PKD2. The similarity in the clinical presentation and evidence of direct interaction between the COOH termini of polycystin-1 and polycystin-2, the respective gene products, suggest that both proteins act in the same molecular pathway. The fact that most mutations from ADPKD patients result in truncated polycystins as well as evidence of a loss of heterozygosity mechanism in individual PKD cysts indicate that the loss of the function of either PKD1 or PKD2 is the most likely pathogenic mechanism for ADPKD. A novel mouse model, WS25, has been generated with a targeted mutation at Pkd2 locus in which a mutant exon 1 created by inserting a neo(r) cassette exists in tandem with the wild-type exon 1. This causes an unstable allele that undergoes secondary recombination to produce a true null allele at Pkd2 locus. Therefore, the model Pkd2(WS25/-), which carries the WS25 unstable allele and a true null allele, produces somatic second hits during mouse development or adult life and establishes an extremely faithful model of human ADPKD.

Racial variation in autosomal dominant polycystic kidney disease

These analyses were undertaken to determine whether racial variation contributes to the risk of end-stage renal disease (ESRD) in close relatives of incident dialysis patients with autosomal dominant polycystic kidney disease (ADPKD)-associated ESRD. A family history of ESRD was recorded in 14,769 incident ESRD patients in Network 6 (Georgia, North Carolina, South Carolina) between September 1993 and November 1997. Two hundred thirty-seven patients with ADPKD-ESRD comprised the study population (180 white and 57 black). Differences in patient populations were analyzed using the chi-squared and Student's t-tests, and multiple regression analysis was performed. Correlation in age at ESRD onset in families was performed by linear regression analysis. A positive family history (FH) of ESRD in first- or second-degree relatives was reported by 38.6% (22 of 57) of blacks and 55% (99 of 180) of whites (P = 0.03). The 22 blacks with a positive FH had a mean of 2.0 additional ESRD relatives and 10.4 total first-degree relatives, whereas the 99 whites with a positive FH had a mean of 2.6 additional ESRD relatives and 7.0 total first-degree relatives (P = 0.14 and P < 0.001, respectively). Mean age in years at first dialysis was similar in blacks and whites, regardless of FH (black FH positive, 63.8; black FH negative, 66.3; P = 0.66; white FH positive, 60.8; white FH negative, 62.8; P = 0. 48). On average, 57.9% of the first- and second-degree relatives of white cases had ADPKD-associated ESRD, compared with 28.6% of the relatives of black cases (P < 0.001). In the multivariate analysis, white race (P = 0.004) and increasing family size (P = 0.002) were positively correlated with the number of relatives having ADPKD-associated ESRD, whereas age at ESRD onset (P = 0.50) and gender (P = 0.94) were not. Age at onset of ESRD was correlated within members of multiply affected white (P < 0.001) but not black families (P = 0.80). We conclude that blacks with ADPKD-associated ESRD are less likely than whites to have relatives with ESRD, and there is no correlation in age at onset of ADPKD-ESRD in black families.

Aberrant splicing in the PKD2 gene as a cause of polycystic kidney disease

It is estimated that approximately 15% of families with autosomal dominant polycystic kidney disease (ADPKD) have mutations in PKD2. Identification of these mutations is central to identifying functionally important regions of gene and to understanding the mechanisms underlying the pathogenesis of the disorder. The current study describes mutations in six type 2 ADPKD families. Two single base substitution mutations discovered in the ORF in exon 14 constitute the most COOH-terminal pathogenic variants described to date. One of these mutations is a nonsense change and the other encodes an apparent missense variant. Reverse transcription-PCR from patient lymphoblast RNA showed that, in addition, both mutations resulted in out-of-frame splice variants by activating cryptic splice sites via different mechanisms. The apparent missense variant produced such a strong splicing signal that the processed transcript from the mutant chromosome did not contain any of the normally spliced, missense product. A third mutation, a nonconservative missense change effecting a negatively charged residue in the third transmembrane span, is likely pathogenic and defines a highly conserved residue consistent with a potential channel subunit function for polycystin-2. The remaining three mutations included two frame shifts resulting from deletion of one or two bases in exons 6 and 10, respectively, and a nonsense mutation due to a single base substitution in exon 4. The study also defined a novel intragenic polymorphism in exon 1 that will be useful in analyzing "second hits" in PKD2. Finally, the study demonstrates that there are reduced levels of normal polycystin-2 protein in lymphoblast lines from PKD2-affected individuals and that truncated mutant polycystin-2 cannot be detected in patient lymphoblasts, suggesting that the latter may be unstable in at least some tissues. The mutations described will serve as critical reagents for future functional studies in PKD2.

Identification and characterization of polycystin-2, the PKD2 gene product

PKD2, the second gene for the autosomal dominant polycystic kidney disease (ADPKD), encodes a protein, polycystin-2, with predicted structural similarity to cation channel subunits. However, the function of polycystin-2 remains unknown. We used polyclonal antisera specific for the intracellular NH(2) and COOH termini to identify polycystin-2 as an approximately 110-kDa integral membrane glycoprotein. Polycystin-2 from both native tissues and cells in culture is sensitive to Endo H suggesting the continued presence of high-mannose oligosaccharides typical of pre-middle Golgi proteins. Immunofluorescent cell staining of polycystin-2 shows a pattern consistent with localization in the endoplasmic reticulum. This finding is confirmed by co-localization with protein-disulfide isomerase as determined by double indirect immunofluorescence and co-distribution with calnexin in subcellular fractionation studies. Polycystin-2 translation products truncated at or after Gly(821) retain their exclusive endoplasmic reticulum localization while products truncated at or before Glu(787) additionally traffic to the plasma membrane. Truncation mutants that traffic to the plasma membrane acquire Endo H resistance and can be biotinylated on the cell surface in intact cells. The 34-amino acid region Glu(787)-Ser(820), containing two putative phosphorylation sites, is responsible for the exclusive endoplasmic reticulum localization of polycystin-2 and is the site of specific interaction with an as yet unidentified protein binding partner for polycystin-2. The localization of full-length polycystin-2 to intracellular membranes raises the possibility that the PKD2 gene product is a subunit of intracellular channel complexes.

Autosomal dominant polycystic kidney disease types 1 and 2: assessment of US sensitivity for diagnosis

PURPOSE

To estimate the sensitivity and specificity of ultrasonography (US) in the diagnosis of autosomal dominant polycystic kidney disease (ADPKD) types 1 and 2, as compared with those of genetic linkage analysis.

MATERIALS AND METHODS

A renal US and DNA analysis for ADPKD was performed in 319 patients who were at risk, 161 of whom were younger than 30 years, from 54 families with ADPKD. The sensitivity of US for diagnosis was estimated by comparing the US results with genotypes inferred from linkage studies.

RESULTS

The sensitivity of US in individuals younger than 30 years who were at risk was 95% for ADPKD type 1 but only 67% for ADPKD type 2. The sensitivity of US for either ADPKD type 1 or ADPKD type 2 in individuals aged 30 years or older who were at risk was 100%. The overall sensitivity in individuals younger than 30 years was 93%. For both ADPKD types 1 and 2 in all patients, US demonstrated a sensitivity of 97%, a specificity of 100%, and an accuracy of 98%.

CONCLUSION

US is the first-line imaging technique that should be used in the diagnosis of ADPKD. The sensitivity in individuals aged 30 years or older is 100%, but if there is a clinical suspicion of ADPKD type 2 in individuals younger than 30 years, linkage analysis should also be considered.

Echocardiographic evaluation in patients with autosomal dominant polycystic kidney disease and end-stage renal disease

Cardiovascular abnormalities have been considered important extrarenal manifestations of autosomal dominant polycystic kidney disease (ADPKD). However, little is known about their prevalence in patients with ADPKD undergoing hemodialysis (HD). To investigate whether cardiac abnormalities are more prevalent in these patients, clinical and echocardiographic manifestations of cardiovascular disease were evaluated in a group of 32 patients with ADPKD and a matched control group of 32 patients without diabetes treated by chronic HD for more than 6 months. Predialysis systolic and diastolic blood pressure (BP), prevalence of hypertension, and number of patients requiring antihypertensive medications were lower in the ADPKD group than controls. There was no difference in the prevalence of cardiac events, including cardiac failure, ischemic heart disease, and arrhythmia. Systolic dysfunction, diastolic patterns, and left ventricular hypertrophy were similar in the two groups. In patients with ADPKD, simple regression analysis showed left ventricular mass (LVM) index was correlated with hemoglobin level and predialytic systolic and diastolic BPs. In multiple regression analysis, predialysis systolic BP was the only independent variable linked to LVM index. The prevalence of aortic, mitral, and tricuspid valve disease did not differ between groups. In conclusion, the occurrence of cardiovascular complications in patients with ADPKD is similar to that of HD patients with other primary renal diseases, although hypertension is less prevalent.

A loss-of-function model for cystogenesis in human autosomal dominant polycystic kidney disease type 2

Autosomal dominant polycystic kidney disease (ADPKD) is genetically heterogeneous, with at least three chromosomal loci (PKD1, PKD2, and PKD3) that account for the disease. Mutations in the PKD2 gene, on the long arm of chromosome 4, are expected to be responsible for approximately 15% of cases of ADPKD. Although ADPKD is a systemic disease, it shows a focal expression, because <1% of nephrons become cystic. A feasible explanation for the focal nature of events in PKD1, proposed on the basis of the two-hit theory, suggests that cystogenesis results from the inactivation of the normal copy of the PKD1 gene by a second somatic mutation. The aim of this study is to demonstrate that somatic mutations are present in renal cysts from a PKD2 kidney. We have studied 30 renal cysts from a patient with PKD2 in which the germline mutation was shown to be a deletion that encompassed most of the disease gene. Loss-of-heterozygosity (LOH) studies showed loss of the wild-type allele in 10% of cysts. Screening of six exons of the gene by SSCP detected eight different somatic mutations, all of them expected to produce truncated proteins. Overall, >/=37% of the cysts studied presented somatic mutations. No LOH for the PKD1 gene or locus D3S1478 were observed in those cysts, which demonstrates that somatic alterations are specific. We have identified second-hit mutations in human PKD2 cysts, which suggests that this mechanism could be a crucial event in the development of cystogenesis in human ADPKD-type 2.

Familial phenotype differences in PKD11

Familial phenotype differences in PKD1.

BACKGROUND

Mutations within the PKD1 gene are responsible for the most common and most severe form of autosomal dominant polycystic kidney disease (ADPKD). Although it is known that there is a wide range of disease severity within PKD1 families, it is uncertain whether differences in clinical severity also occur among PKD1 families.

METHODS

Ten large South Wales ADPKD families with at least 12 affected members were included in the study. From affected members, clinical information was obtained, including survival data and the presence of ADPKD-associated complications. Family members who were at risk of having inherited ADPKD but were proven to be non-affected were included as controls. Linkage and haplotype analysis were performed with highly polymorphic microsatellite markers closely linked to the PKD1 gene. Survival data were analyzed by the Kaplan-Meier method and the log rank test. Logistic regression analysis was used to test for differences in complication rates between families.

RESULTS

Haplotype analysis revealed that each family had PKD1-linked disease with a unique disease-associated haplotype. Interfamily differences were observed in overall survival (P = 0.0004), renal survival (P = 0.0001), hypertension prevalence (P = 0.013), and hernia (P = 0.048). Individuals with hypertension had significantly worse overall (P = 0.0085) and renal (P = 0.03) survival compared with those without hypertension. No statistically significant differences in the prevalence of hypertension and hernia were observed among controls.

CONCLUSION

We conclude that phenotype differences exist between PKD1 families, which, on the basis of having unique disease-associated haplotypes, are likely to be associated with a heterogeneous range of underlying PKD1 mutations.

Seven novel mutations of the PKD2 gene in families with autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is genetically heterogeneous, with at least three chromosomal loci accounting for the disease. Mutations in the PKD2 gene on the long arm of chromosome 4 are expected to be responsible for approximately 15% of cases of ADPKD.

METHODS

We report a systematic screening for mutations covering the 15 exons of the PKD2 gene in eight unrelated families with ADPKD type 2, using the heteroduplex technique.

RESULTS

Seven novel mutations were identified and characterized that, together with the previously described changes, amount to a detection rate of 85% in the population studied. The newly described mutations are two nonsense mutations, a 1 bp deletion, a 1 bp insertion, a mutation that involves both a substitution and a deletion (2511AG-->C), a complex mutation in exon 6 consisting of a simultaneous 7 bp inversion and a 4 bp deletion, and the last one is a G-->C transversion that may be a missense mutation. Most of these mutations are expected to lead to the formation of shorter truncated proteins lacking the carboxyl terminus of PKD2. We have also characterized a frequent polymorphism, Arg-Pro, at codon 28 in this gene. The clinical features of these PKD2 patients are similar to the previously described, with the mean age of end-stage renal disease being 75.5 years (SE +/- 3.8 years).

CONCLUSIONS

Our results confirm that many different mutations are likely to be responsible for the disease and that most pathogenic defects probably are point or small changes in the coding region of the gene.

Polycystin-2 expression is developmentally regulated

PKD2 encodes a protein of unknown function that is mutated in 15% of autosomal dominant polycystic kidney disease (ADPKD) families. We used polyclonal antisera against PKD2 to examine the pattern of Pkd2 expression in staged mouse embryos. Staining for Pkd2 was documented as early as the 6th embryonic day (day E6) in the embryonic ectoderm and endoderm. Low-intensity staining is seen in metanephric ureteric bud at day E12.5. By day E15.5, the adult pattern of expression is established with low level staining in proximal tubules and high level, basolateral staining in distal tubules. Pkd2 expression is first detected in the medullary collecting ducts at postnatal day 14. Outside of the kidney, Pkd2 expression is widely distributed in utero and more restricted postnatally. The greatest intensity of staining is seen in the fetal but not adult adrenal cortex and in red blood cell precursors. Expression also is seen in multiple endocrine organs, in cardiac, skeletal, and smooth muscle, and in multiple mesenchymal tissues. The diffuse distribution and early expression of Pkd2 suggest a fundamental developmental role. The persistent strong expression in adult kidney is consistent with a more organ-specific function in the maintenance of the mature metanephric tubule.

Polycystic kidney disease in bull terriers: an autosomal dominant inherited disorder

The prevalence, mode of inheritance and urinalysis findings in Bull Terriers with polycystic kidney disease were assessed by screening 150 clinically normal dogs. The disorder was diagnosed in 39 dogs on the basis of renal ultrasound results and family history of the disease. In equivocal cases confirmation required gross and histopathological renal examination. Necropsy was performed on nine affected dogs and the kidneys from another five affected animals were also examined. Renal cysts were usually bilateral, occurred in cortex and medulla and varied from less than 1 mm to over 2.5 cm in diameter. Cysts were lined by epithelial cells of nephron origin. Abnormal urine sediment and proteinuria were common in affected dogs. The disease appears to be inherited in a highly penetrant autosomal dominant manner.

Evaluation of autosomal dominant polycystic kidney disease by DTPA renal scintigraphy

Sixty patients with previously documented autosomal dominant polycystic kidney disease (ADPKD) were investigated using dynamic kidney scintigraphy with 99mTc-diethylenetriaminepentaacetic acid (DTPA). Patients were subdivided in respect of glomerular filtration rate (GFR) as follows: PKD I group (normal GFR), PKD II group (moderately reduced GFR), and PKD III (severely reduced GFR). Scintigraphic features, time activity curves, excretion parameters, global and individual kidney functions were analyzed. Because of GFR dependent sensitivity, in advanced renal failure being only 0.1, and low reproducibility (11% intraobserver, 22% interobserver), 99mTc-DTPA dynamic kidney scintigraphy cannot be generally recommended for the diagnosis of ADPKD, but has to become a routine method for functional evaluation of both global and individual renal functions, as well as degree of excretion disturbances in ADPKD patients.

Comparison of phenotypes of polycystic kidney disease types 1 and 2. European PKD1-PKD2 Study Group

BACKGROUND

Although autosomal dominant polycystic kidney disease type 2 (PKD2) is known to have a milder clinical phenotype than PKD1, neither disorder has been compared with an unaffected control population in terms of survival. We report the findings of a multicentre survey that aimed to define more precisely the survival and clinical expression of PKD1 and PKD2.

METHODS

Clinical data from 333 people with PKD1 (31 families) were compared with data from 291 people with PKD2 (31 families) and 398 geographically matched controls. Survival analysis was used to compare age-at-event data. Differences in the prevalence of complications were assessed by logistic regression.

FINDINGS

Median age at death or onset of end-stage renal disease was 53.0 years (95% CI 51.2-54.8) in individuals with PKD1, 69.1 years (66.9-71.3) in those with PKD2, and 78.0 years (73.8-82.2) in controls. Women with PKD2 had a significantly longer median survival than men (71.0 [67.4-74.8] vs 67.3 [64.9-69.7] years), but no sex influence was apparent in PKD1. Age at presentation with kidney failure was later in PKD2 than in PKD1 (median age 74.0 [67.2-80.8] vs 54.3 [52.7-55.9] years). PKD2 patients were less likely to have hypertension (odds ratio 0.25 [95% CI 0.15-0.42]), a history of urinary-tract infection (0.50 [0.31-0.83]), or haematuria (0.59 [0.35-0.98]).

INTERPRETATION

Although PKD2 is clinically milder than PKD1, it has a deleterious impact on overall life expectancy and cannot be regarded as a benign disorder.