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

Polycystin-2 (TRPP2): Ion channel properties and regulation

Polycystin-2 (TRPP2, PKD2, PC2) is the product of the PKD2 gene, whose mutations cause Autosomal Dominant Polycystic Kidney Disease (ADPKD). PC2 belongs to the superfamily of TRP (Transient Receptor Potential) proteins that generally function as Ca²⁺-permeable nonselective cation channels implicated in Ca²⁺ signaling. PC2 localizes to various cell domains with distinct functions that likely depend on interactions with specific channel partners. Functions include receptor-operated, nonselective cation channel activity in the plasma membrane, intracellular Ca²⁺ release channel activity in the endoplasmic reticulum (ER), and mechanosensitive channel activity in the primary cilium of renal epithelial cells. Here we summarize our current understanding of the properties of PC2 and how other transmembrane and cytosolic proteins modulate this activity, providing functional diversity and selective regulatory mechanisms to its role in the control of cellular Ca²⁺ homeostasis.

Risk of Hospital Encounters With Kidney Stones in Autosomal Dominant Polycystic Kidney Disease: A Cohort Study

Background:

There is a perception that patients with autosomal dominant polycystic kidney disease (ADPKD) are more likely to develop kidney stones than the general population.

Objective:

To compare the rate of hospital encounter with kidney stones and the rate of stone interventions between patients with and without ADPKD.

Design:

Retrospective cohort study.

Setting:

Ontario, Canada.

Patients:

Patients with and without ADPKD who had a prior hospital encounter between 2002 and 2016.

Measurements:

Rate of hospital encounter with kidney stones and rate of stone intervention.

Methods:

We used inverse probability exposure weighting based on propensity scores to balance baseline indicators of health between patients with and without ADPKD. We followed each patient until death, emigration, outcomes, or March 31, 2017. We used a Cox proportional hazards model to compare event rates between the two groups.

Results:

Patients with ADPKD were at higher risk of hospital encounter with stones compared with patients without ADPKD (81 patients of 2094 with ADPKD [3.8%] vs 60 patients of 1902 without ADPKD [3.2%]; 8.9 vs 5.1 events per 1000 person-years; hazard ratio 1.6 [95% CI, 1.3-2.1]). ADPKD was not associated with a higher risk of stone intervention (49 of 2094 [2.3%] vs 47 of 1902 [2.4%]; 5.3 vs 3.9 events per 1000 person-years; hazard ratio 1.2 [95% CI = 0.9-1.3]).

Limitations:

We did not have information on kidney stone events outside of the hospital. There is a possibility of residual confounding.

Conclusion:

ADPKD was a significant risk factor for hospital encounters with kidney stones.

Spontaneous Coronary Artery Dissection: Insights on Rare Genetic Variation From Genome Sequencing

Supplemental Digital Content is available in the text.

Spontaneous coronary artery dissection (SCAD) occurs when an epicardial coronary artery is narrowed or occluded by an intramural hematoma. SCAD mainly affects women and is associated with pregnancy and systemic arteriopathies, particularly fibromuscular dysplasia. Variants in several genes, such as those causing connective tissue disorders, have been implicated; however, the genetic architecture is poorly understood. Here, we aim to better understand the diagnostic yield of rare variant genetic testing among a cohort of SCAD survivors and to identify genes or gene sets that have a significant enrichment of rare variants.

Stone Prevalence in Autosomal Dominant Polycystic Kidney Disease: A Systematic Review and Meta-Analysis

Background:

It is uncertain how often patients with autosomal dominant polycystic kidney disease (ADPKD) develop kidney stones.

Objective:

To review English-language studies reporting the incidence and prevalence of stones and stone interventions in adults with ADPKD.

Design:

Systematic review and meta-analysis.

Setting:

Any country of origin.

Patients:

Adult patients with ADPKD.

Measurements:

Incidence or prevalence of kidney stones and stone interventions.

Methods:

We reviewed 1812 citations from bibliographic databases, abstracted data from 49 eligible studies, and assessed methodological quality in duplicate. In some studies, the proportion of adults with ADPKD with the outcome were compared to adults without ADPKD; for these studies, prevalence risk ratios were calculated and pooled using a random effects model.

Results:

We identified 49 articles that met our review criteria. The methodological quality of many studies was limited (scores ranging from 2 to 14 out of 22, with a higher score indicating higher quality). No study clearly reported stone incidence, and in the cross-sectional studies, the definition of stones was often unclear. The prevalence of stones ranged from 3% to 59%, and a prevalence of stone interventions ranged from 1% to 8%; the average patient age at the time of assessment ranged from 26 to 61 years across the studies. Two studies reported a nonstatistically significant higher stone prevalence in patients with ADPKD compared to unaffected family members. Compared to unaffected family members, patients with ADPKD had a higher prevalence of kidney stones (6 cross-sectional studies; unadjusted prevalence ratio: 1.8; 95% confidence interval: 1.3 to 2.6; P = .0007; test for heterogeneity: I² = 0%, P = .8).

Limitations:

Studies were limited to articles published in English.

Conclusions:

The prevalence of kidney stones and stone interventions in adults with ADPKD remains uncertain. Future studies of higher methodological quality are needed to better characterize the incidence and prevalence of kidney stones in patients with ADPKD.

Trial registration:

We did not register the protocol for this systematic review.

Ruptured Berry Aneurysm as the initial presentation of Polycystic Kidney Disease: A case report and review of literature

Intra-cranial saccular aneurysms, also known as Berry aneurysms, have a well-known association with autosomal dominant polycystic kidney disease (ADPKD). Aneurysmal rupture can be the initial presentation of the disease. ADPKD has two types of gene mutations: PKD1 and PKD2. The latter one is of a milder form presenting later in life. Imaging plays a crucial role in the diagnosis and assessment in order to provide adequate management of these patients however, there are no official standardized guidelines established for screening of these intracranial aneurysms.

Hypertension in autosomal dominant polycystic kidney disease: a meta-analysis

CONTEXT

Autosomal dominant polycystic kidney disease (ADPKD) is a common disorder that can cause hypertension during childhood, but the true prevalence of hypertension during childhood is not known.

OBJECTIVE

We undertook a systematic review and meta-analysis to determine the prevalence of hypertension in children with ADPKD.

DATA SOURCES

Systematic review of articles published between 1980 and 2015 in MEDLINE and EMBASE.

STUDY SELECTION

Studies selected by two authors independently if reporting data on prevalence of hypertension in children and young persons aged <21 years with a diagnosis of ADPKD. Observational series were included with study populations of >15 children. Articles were excluded if inadequate diagnostic criteria for hypertension were used. Studies with selection bias were included but analysed separately.

DATA EXTRACTION

Data extracted on prevalence of hypertension, proteinuria and reduced renal function using standardised form. Meta-analysis was performed to calculate weighted mean prevalence.

RESULTS

903 articles were retrieved from our search; 14 studies met the inclusion criteria: 1 prospective randomised controlled trial; 8 prospective observational studies; and 5 retrospective cross-sectional studies. From 928 children with clinically confirmed ADPKD, 20% (95% CI 15% to 27%) were hypertensive. The estimated prevalence of proteinuria in children with ADPKD is 20% (8 studies; 95% CI 9% to 40%) while reduced renal function occurred in 8% (5 studies; 95% CI 2% to 26%).

LIMITATIONS

Studies showed a high degree of methodological heterogeneity (I²=73.4%, τ²=0.3408, p<0.0001). Most studies did not use ambulatory blood pressure (BP) monitoring to diagnose hypertension.

CONCLUSIONS

In this meta-analysis we estimate 20% of children with ADPKD have hypertension. In the population, many children with ADPKD are not under regular follow-up and remain undiagnosed. We recommend that all children at risk of ADPKD have regular BP measurement.

Diagnostic Imaging of Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common genetic disorders caused by a single gene mutation. The disease usually manifests itself at the age of 30-40 years and is characterized by formation of renal cysts along with the enlargement of kidneys and deterioration of their function, eventually leading to renal insufficiency. Imaging studies (sonography, computed tomography, magnetic resonance imaging) play an important role in the diagnostics of the disease, the monitoring of its progression, and the detection of complications. Imaging is also helpful in detecting extrarenal manifestations of ADPKD, most significant of which include intracranial aneurysms and cystic liver diseases.

A Case of New Familiar Genetic Variant of Autosomal Dominant Polycystic Kidney Disease-2: A Case Study

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is characterized by renal cyst formation due to mutations in genes coding for polycystin-1 [PKD1 (85-90% of cases), on ch 16p13.3] and polycystin-2 [PKD2 (10-15% of cases), on ch 4q13-23] and PKD3 gene (gene unmapped). It is also associated with TSC2/PKD1 contiguous gene syndrome. ADPKD is usually inherited, but new mutations without a family history occur in approximately 10% of the cases.

CASE PRESENTATION

A 17-year-old boy was followed up for bilateral cystic kidney disease, hypertension, and obesity since he was 13 years old. The diagnosis was an accidental finding during abdominal CT at age 13 to rule out appendicitis. A renal ultrasonogram also demonstrated a multiple bilateral cysts. Because of parental history of bilateral renal cysts, PKD1 and PKD2, genetic testing was ordered. Results showed, PKD2 variant 1:3 bp deletion of TGT; nucleotide position: 1602-1604; codon position: 512-513; mRNA reading frame maintained. The same mutation was later identified in his father.

CONCLUSION

A smaller number of patients have a defect in the PKD2 locus on chromosome 4 (resulting in PKD2 disease). There are no known published cases on this familiar genetic variant of ADPKD-2 cystic kidney disease. In this case, the disease is present unusually early in life.

Autosomal dominant polycystic kidney disease: recent advances in pathogenesis and potential therapies

Autosomal dominant polycystic kidney disease (ADPKD) is the most common progressive hereditary kidney disease. In 85-90% of cases, ADPKD results from a mutation in the PKD1 gene, and the other 10-15% of the cases are accounted for by mutations in PKD2. PKD1 and PKD2 encode polycystin-1 and polycystin-2. Polycystin-1 may be a receptor that controls the channel activity of polycystin-2 as part of the polycystin signaling complex. ADPKD is characterized by the progressive development of fluid-filled cysts derived from renal tubular epithelial cells that gradually compress the parenchyma and compromise renal function. In recent years, considerable interest has developed in the primary cilia as a site of the proteins that are involved in renal cystogenesis. The pathological processes that facilitate cyst enlargement are hypothesized to result from two specific cellular abnormalities: (1) increased fluid secretion into the cyst lumen and (2) inappropriately increased cell division by the epithelium lining the cyst. Since there is no clinically approved specific or targeted therapy, current practice focuses on blood pressure control and statin therapy to reduce the cardiac mortality associated with chronic kidney disease. However, recent advances in our understanding of the pathways that govern renal cystogenesis have led to a number of intriguing possibilities in regard to therapeutic interventions. The purpose of this article is to review the pathogenesis of renal cyst formation and to review novel targets for the treatment of ADPKD.

[Cystic and hyperechogenic kidneys in children]

Thanks to prenatal ultrasound scan, cystic kidneys, as well as obstructive uropathies, are the most frequent renal anomalies identified during pregnancy. They should be recognized because of genetic and clinical implications. The most frequent are autosomal dominant and recessive polycystic kidney diseases, followed by renal developmental anomalies linked to TCF2 gene. Renal cysts are also observed in other hereditary diseases or multiple malformation syndromes (tuberosis sclerosis, Meckel-Grubber syndrome, Oro-facial digital type 1 syndrome...). The diagnosis is based on a sonographic and morphological analysis of renal abnormalities, on the search for family histories and extra-renal manifestations. A better classification of these patients allows tailor-made follow-up and care improvement.

Cystic diseases of the kidney: molecular biology and genetics

CONTEXT

Cystic diseases of the kidney are a very heterogeneous group of renal inherited conditions, with more than 33 genes involved and encompassing X-linked, autosomal dominant, and autosomal recessive inheritance. Although mostly monogenic with mendelian inheritance, there are clearly examples of oligogenic inheritance, such as 3 mutations in 2 genes, while the existence of genetic modifiers is perhaps the norm, based on the extent of variable expressivity and the broad spectrum of symptoms.

OBJECTIVES

To present in the form of a mini review the major known cystic diseases of the kidney for which genes have been mapped or cloned and characterized, with some information on their cellular and molecular biology and genetics, and to pay special attention to commenting on the issues of molecular diagnostics, in view of the genetic and allelic heterogeneity. Data Sources.-We used major reviews that make excellent detailed presentation of the various diseases, as well as original publications.

CONCLUSIONS

There is already extensive genetic heterogeneity in the group of cystic diseases of the kidney; however, there are still many more genes awaiting to be discovered that are implicated or mutated in these diseases. In addition, the synergism and interaction among this repertoire of gene products is largely unknown, while a common unifying aspect is the expression of nearly all of them at the primary cilium or the basal body. A major interplay of functions is anticipated, while mutations in all converge in the unifying phenotype of cyst formation.

Treatment of autosomal dominant polycystic kidney disease (ADPKD): the new horizon for children with ADPKD

Polycystic kidney disease (PKD) is the most common inherited renal disorder. Patients with PKD remain clinically asymptomatic for decades, while significant anatomic and physiologic systemic changes take place. Sequencing of the responsible genes and identification of their protein products have significantly expanded our understanding of the pathophysiology of PKD. The molecular basis for cystogenesis is being unraveled, leading to new targets for therapy and giving hope to millions of people suffering from PKD. This has direct implications for children with PKD with regard to screening for the disease and identification of high-risk individuals. In this article we provide a review of the clinical manifestations in children with autosomal dominant polycystic kidney disease (ADPKD), the genetic and molecular basis for the disease, and a concise review of potential therapies being evaluated.

COL4A3/COL4A4 mutations producing focal segmental glomerulosclerosis and renal failure in thin basement membrane nephropathy

Mutations in the COL4A3/COL4A4 genes of type IV collagen have been found in approximately 40% of cases of thin basement membrane nephropathy, which is characterized by microscopic hematuria and is classically thought to cause proteinuria and chronic renal failure rarely. Here we report our observations of 116 subjects from 13 Cypriot families clinically affected with thin basement membrane nephropathy. These families first came to our attention because they segregated microscopic hematuria, mild proteinuria, and variable degrees of renal impairment, but a dual diagnosis of focal segmental glomerulosclerosis (FSGS) and thin basement membrane nephropathy was made in 20 biopsied cases. Molecular studies identified founder mutations in both COL4A3 and COL4A4 genes in 10 families. None of 82 heterozygous patients had any extrarenal manifestations, supporting the diagnosis of thin basement membrane nephropathy. During follow-up of up to three decades, 31 of these 82 patients (37.8%) developed chronic renal failure and 16 (19.5%) reached end-stage renal disease. Mutations G1334E and G871C were detected in seven and three families, respectively, and were probably introduced by founders. We conclude that these particular COL4A3/COL4A4 mutations either predispose some patients to FSGS and chronic renal failure, or that thin basement membrane nephropathy sometimes coexists with another genetic modifier that is responsible for FSGS and progressive renal failure. The findings presented here do not justify the labelling of thin basement membrane nephropathy as a benign condition with excellent prognosis.

Autosomal Dominant Polycystic Kidney Disease: Time for a Change?

Diagnosis and treatment of autosomal dominant polycystic kidney disease (ADPKD) is rapidly changing. Cellular pathways that involve the polycystins are being mapped and involve the primary cilium, intracellular calcium and cAMP regulation, and the mammalian target of rapamycin (mTOR) pathway. With the use of new imaging approaches, earlier diagnosis of hepatic cystic disease is possible, and measurement of kidney and cystic growth as well as kidney blood flow is possible over relatively short periods. PKD gene type, gender, proteinuria, and the presence of hypertension relate to the rate of kidney growth in ADPKD. On the basis of risk factors for progression to ESRD and the pathogenic roles that intracellular cAMP and mTOR play in cystogenesis, novel therapies are now being tested, including maximal inhibition of the renin-angiotensin system, inhibition of renal intracellular cAMP using vasopressin V2 receptor antagonists, and somatostatin analogues, as well as inhibitors of mTOR. This review addresses the current understanding of the pathogenesis and the natural history of ADPKD; accuracy and reliability of diagnostic approaches in utero, childhood, and adulthood; the value of reliable magnetic resonance imaging to measure disease progression early in the course of ADPKD; and novel therapeutic approaches that are being evaluated in ADPKD.

[Polycystic kidney diseases: molecular genetics and counselling]

Autosomal dominant polycystic kidney disease (ADPKD) affects 1 newborn in 400 to 1000 making it the most common inherited form of genetic kidney disease and an important cause of medical morbidity and account for about 10% of end-stage renal disease. Autosomal recessive polycystic kidney disease (ARPKD) is a rare (1/20,000 to 1/40,000) inherited disease in children characterized by the association of dilation of collecting ducts and biliary dysgenesis. The clinical spectrum is variable but it represents an important cause of renal and liver-related morbidity and mortality in neonates and infancy. Symptoms of autosomal recessive PKD can begin before birth. ARPKD is genetically different from ADPKD. Parents who do not have the disease can have a child with the disease if both parents carry the abnormal gene and both pass the gene to their baby. Recently important advances in understanding the molecular basis of ADPKD (i.e. ADPKD1 and ADPKD2) and autosomal recessive PKD (i.e. PKHD1) have been done and are reported here. Genetic counselling is particularly advised in early onset disease families. It permits to determine the type of transmission, to describe the course and the major complications of the disease and to explain currents therapeutics possibilities.

Perinatal assessment of hereditary cystic renal diseases: the contribution of sonography

The aims of this review article were to clarify the steps that may lead to a proper diagnosis of fetal and neonatal renal cystic diseases. All the hereditary cystic diseases are reviewed and a classification is proposed. The various sonographic patterns that can be used to ascertain the diagnosis are also reviewed. Finally, tables with differential diagnoses are presented to help the reader in the work-up of such pathologies.

Pain patterns in patients with polycystic kidney disease

BACKGROUND

Pain is a common problem in patients with polycystic kidney disease (PKD), but patterns have not been characterized as to frequency and severity. Physicians should be aware of pain problems so an approach to chronic pain management can be pursued.

METHODS

One hundred seventy-one completed questionnaires out of 300 distributed to PKD patients whose renal function ranged from normal to end-stage renal disease (ESRD) were analyzed. Age at diagnosis of PKD was documented, and patients noted how the diagnosis was made. Location, severity, and frequency of pain were characterized. The Visual Analogue Scale (VAS) was used to measure pain intensity.

RESULTS

There were 94 females and 77 male respondents, with a mean age of 47.4 years. Initial diagnosis of PKD occurred at a mean age of 31.6 years. Caucasians comprised 92.2% of the respondents. Patients' symptoms, a family history of PKD, and discovery of PKD during evaluation for hypertension or hematuria were the most frequent factors that led to the diagnosis. Order of frequency of pain was: low back pain, abdominal pain, headache, chest pain, and leg pain. Severity of pain, documented by the VAS intensity, was 4 to 5/10 in the majority of patients.

CONCLUSION

Pain, which can be diffuse, is the most frequent symptom that led to the diagnosis of PKD in patients who responded to this questionnaire, and occurs with greater frequency than generally appreciated. Physicians need to obtain a detailed history about pain in their PKD population so as to allow an approach to pain management.

Autosomal dominant polycystic kidney disease (ADPKD, MIM 173900, PKD1 and PKD2 genes, protein products known as polycystin-1 and polycystin-2)

Autosomal dominant polycystic kidney disease (ADPKD) is a common inherited nephropathy affecting over 1:1000 of the worldwide population. It is a systemic condition with frequent hepatic and cardiovascular manifestations in addition to the progressive development of renal cysts that eventually result in loss of renal function in the majority of affected individuals. The diagnosis of ADPKD is typically made using renal imaging despite the identification of mutations in PKD1 and PKD2 that account for virtually all cases. Mutations in PKD1 are associated with more severe clinical disease and earlier onset of renal failure. Most PKD gene mutations are loss of function and a 'two-hit' mechanism has been demonstrated underlying focal cyst formation. The protein products of the PKD genes, the polycystins, form a calcium-permeable ion channel complex that regulates the cell cycle and the function of the renal primary cilium. Abnormal cilial function is now thought to be the primary defect in several types of PKD including autosomal recessive polycystic kidney disease and represents a novel and exciting mechanism underlying a range of human diseases.

Prenatal sonographic patterns in autosomal dominant polycystic kidney disease: a multicenter study

OBJECTIVE

To determine whether a specific prenatal sonographic pattern can be identified for autosomal dominant polycystic kidney disease (ADPKD) and if so whether it would be helpful in orienting complementary analysis, properly counseling parents and adapting pregnancy management.

METHODS

A retrospective multicenter study was conducted in four prenatal diagnostic centers. The records of fetuses with a prenatal ultrasound examination revealing abnormal kidneys and with a final diagnosis of ADPKD were analyzed. Ultrasound analysis included: amount of amniotic fluid, bladder size, renal length, presence or absence of renal cysts and size of renal pelves, and was focused on parenchyma echogenicity and status of corticomedullary differentiation. Postnatal follow-up was reviewed.

RESULTS

Of the 27 patients included in the study, 25 had hyperechogenic renal cortex and 20 had hypoechogenic medulla resulting in increased corticomedullary differentiation (CMD). In six cases, the medulla was hyperechogenic leading to absent or decreased CMD. One patient had normal cortical echogenicity and CMD. Renal cysts were present during the prenatal period in four patients (at 22 weeks in one case and after 30 weeks in three cases). In 12 patients, the cysts appeared after birth (within the first 6 months of postnatal life in 10 cases and by the age of 1 year in two cases). Elevated blood pressure was observed in only two cases and moderate chronic renal failure in one case.

CONCLUSION

We have described the sonographic presentation in fetuses with ADPKD: moderately enlarged hyperechogenic kidneys with increased CMD. Although not specific to ADPKD, these findings should prompt familial screening. Other prenatal sonographic features (absent or decreased CMD and cortical cysts) are less frequent.

Progression of kidney disease varies between families with defects in the polycystic kidney disease type 1 gene in eastern Finland

OBJECTIVE

To characterize, for the first time, the phenotype and clinical course of autosomal dominant polycystic kidney disease (ADPKD) in Finnish patients.

MATERIAL AND METHODS

All patients underwent an abdominal sonographic examination and most of those with ADPKD underwent magnetic resonance angiography of the head. Haplotype analysis was used to classify 20 ADPKD families into those with defects in either the polycystic kidney disease type 1 (PKD1) or polycystic kidney disease type 2 (PKD2) genes. Evaluation of the rate of progression of kidney disease in patients with ADPKD was based on creatinine values.

RESULTS

Haplotype analysis showed that 16 families had defects in the PKD1 gene and one had defects in the PKD2 gene. Three families were excluded because of uninformative haplotypes. The final study population consisted of 79 unaffected family members, 109 patients with defects in the PKD1 gene and 10 with defects in the PKD2 gene. Higher prevalences of hepatic cysts (3% in healthy relatives, 60% in PKD1 patients and 90% in PKD2 patients; p < 0.001), subarachnoid hemorrhage or cerebral aneurysms (1%, 12% and 0%, respectively; p < 0.001), proteinuria (1%, 23% and 0%, respectively; p < 0.001) and hematuria (5%, 30% and 0%, respectively; p < 0.001) were found in PKD1 patients compared to the healthy relatives. PKD1 patients had a faster progression of kidney disease than PKD2 patients (p < 0.001). The progression of kidney disease varied substantially among the PKD1 families.

CONCLUSION

The relative proportions of PKD1 and PKD2 patients and the phenotype of ADPKD were similar in our Finnish patients compared to previous studies in other populations. However, the progression of kidney disease differed substantially among PKD1 families, indicating a heterogeneic genetic background of PKD1 in Finnish patients.

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.

Ultrasonography in chronic renal failure

Many chronic renal diseases lead to the final common state of decrease in renal size, parenchymal atrophy, sclerosis and fibrosis. The ultrasound image show a smaller kidney, thinning of the parenchyma and its hyperechogenicity (reflecting sclerosis and fibrosis). The frequency of renal cysts increases with the progression of the disease. Ultrasound generally does not allow for the exact diagnosis of an underlying chronic disease (renal biopsy is usually required), but it can help to determine an irreversible disease, assess prognosis and avoid unnecessary diagnostic or therapeutic procedures. The main exception in which the ultrasound image does not show a smaller kidney with parenchymal atrophy is diabetic nephropathy, the leading cause of chronic and end-stage renal failure in developed countries in recent years. In this case, both renal size and parenchymal thickness are preserved until end-stage renal failure. Doppler study of intrarenal vessels can provide additional information about microvascular and parenchymal lesions, which is helpful in deciding for or against therapeutic intervention and timely planning for optimal renal replacement therapy option.

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.

Current advances in molecular genetics of autosomal-dominant polycystic kidney disease

Autosomal-dominant polycystic kidney disease results from at least two causal genes, PKD1 and PKD2. The identical clinical phenotype in human patients and targeted Pkd1 and Pkd2 mutant mouse models provides evidence that both gene products act in the same pathogenic pathway. The discovery of direct PKD1 and PKD2 interactions implies that both gene products, polycystin-1 and polycystin-2, play a functional role in the same molecular complex. The spectrum of germ-line mutations in both genes and the somatic mutations identified from individual PKD1 or PKD2 cysts indicate that loss of function of either PKD1 or PKD2 is the mechanism of cystogenesis in autosomal-dominant polycystic kidney disease. A novel mouse model, Pkd2WS25/-, has proved that loss of heterozygosity is the molecular mechanism of autosomal-dominant polycystic kidney disease. Recently, studies on the expression patterns of PKD1 and PKD2 in humans or mice indicate that polycystin 1 and polycystin 2 seem to have their own respective functional roles, even though most of the functions of these polycystins are parallel during human and mouse development. Pkd2-deficient mice have cardiac septum defects, but Pkd1 knockout mice do not have this phenotype. On the other hand, Pkd2 has a very low level of expression in the central nervous system when compared with Pkd1. In addition, the level of expression of Pkd1 is increased during mesenchymal condensation, whereas Pkd2 expression is unchanged. Preliminary data have shown that the PKD1/PKD2 compound trans-heterozygous has a more severe cystic phenotype in the kidney than that of an age-matched heterozygous type 1 or type 2 of autosomal-dominant polycystic kidney disease alone. This finding suggests that PKD1 may be a modifier of disease severity for PKD2, and vice versa. The characteristics of the contiguous PKD1/TSC2 syndrome phenotypes and the data from Krd mice imply that TSC2 and PAX2 may also serve as potential modifiers for the disease severity of autosomal-dominant polycystic kidney disease.