Facilitated diagnosis of the contiguous gene syndrome: tuberous sclerosis and polycystic kidneys by means of haplotype studies

Molecular diagnosis of an infant with TSC2/PKD1 contiguous gene syndrome

A 1-month-old Japanese infant with cardiac rhabdomyoma was diagnosed with TSC2/PKD1 contiguous gene syndrome by targeted panel sequencing with subsequent quantitative polymerase chain reaction that revealed gross monoallelic deletion, including parts of two genes: exons 19-42 of TSC2 and exons 2-46 of PKD1. Early molecular diagnosis can help to detect bilateral renal cyst formation and multidisciplinary follow-up of this multisystem disease.

TSC2/PKD1 contiguous gene syndrome, with emphasis on a case with an atypical mild polycystic kidney phenotype and a novel genetic variant

About 80% of patients with tuberous sclerosis complex (TSC) present renal involvement, usually as angiomyolipomas followed by cystic disease. An early diagnosis of polycystic kidney disease (PKD) in such patients is frequently related to the TSC2/PKD1 contiguous gene syndrome (PKDTS). Molecular confirmation of PKDTS is important for a prompt diagnosis, which can be complicated by the phenotypic heterogeneity of PKD and the absence of a clear phenotype-genotype correlation. Herein, we report three PKDTS pediatric patients. The case 3 did not present a classic PKDTS phenotype, having only one observable cyst on renal ultrasound at age 4 and multiple small cysts on magnetic resonance imaging at age 15. In this patient, chromosomal microarray analysis showed a gross deletion of 230.8kb that involved TSC2, PKD1 and 13 other protein-coding genes, plus a heterozygous duplication of a previously undescribed copy number variant of 242.9kb that involved six protein-coding genes, including SSTR5, in the 16p13.3 region. Given the observations that the case 3 presented the mildest renal phenotype, harbored three copies of SSTR5, and the reported inhibition of cystogenesis (specially in liver) observed with somatostatin analogs in some patients with autosomal dominant PKD, it can be hypothesized that other genetic factors as the gene dosage of SSTR5 may influence the PKD phenotype and the progression of the disease; however, future work is needed to examine this possibility.

Establishment of a Regional Interdisciplinary Medical System for Managing Patients with Tuberous Sclerosis Complex (TSC)

Tuberous sclerosis complex (TSC) is an autosomal dominant inherited disease characterized by lesions that involve multiple organs. Interdisciplinary management at individual facilities needs to be coordinated to treat multiple organ systems. We hypothesized that the number of patients, opportunities for patients to undergo examinations, and opportunities for patients to be treated would increase after establishment of a TSC board (TB) in our hospital. From August 1979 to August 2017, 76 patients were studied. We established the TB in our hospital in 2014. We divided the patients into the pre-TB group and post-TB group. Patients consisted of 33 females and 43 males (mean age, 18.7 years; median age, 15 years). The follow-up period was 2 to 457 months (mean, 51.6 months; median, 24.5 months). Twenty-four patients were in the pre-TB group, and 52 were in the post-TB group. Regular follow-up (p < 0.001), younger age (p = 0.002), opportunities for patients to undergo examinations, opportunities for patients to receive neurological treatment (p < 0.001), and mammalian target of rapamycin (mTOR) inhibitor usage (p = 0.041) were significantly higher in the post-TB group. The radial relationship around the axis of TSC coordinators may be the key to interdisciplinary management of TSC.

Insight into response to mTOR inhibition when PKD1 and TSC2 are mutated

Background

Mutations in TSC1 or TSC2 cause the tuberous sclerosis complex (TSC), while mutations in PKD1 or PKD2 cause autosomal dominant polycystic kidney disease (ADPKD). PKD1 lays immediately adjacent to TSC2 and deletions involving both genes, the PKD1/TSC2 contiguous gene syndrome (CGS), are characterized by severe ADPKD, plus TSC. mTOR inhibitors have proven effective in reducing angiomyolipoma (AML) in TSC and total kidney volume in ADPKD but without a positive effect on renal function.

Methods and results

We describe a patient with independent truncating PKD1 and TSC2 mutations who has the expected phenotype for both diseases independently instead of the severe one described in PKD1/TSC2-CGS. Treatment with mTOR inhibitors reduced the AML and kidney volume for 2 years but thereafter they resumed growth; no positive effect on renal function was seen throughout. This is the first case addressing the response to mTOR treatment when independent truncating mutations in PKD1 and TSC2 are present.

Conclusions

This case reveals that although PKD1 and TSC2 are adjacent genes and there is likely cross-talk between the PKD1 and TSC2 signalling pathways regulating mTOR, having independent TSC2 and PKD1 mutations can give rise to a milder kidney phenotype than is typical in PKD1/TSC2-CGS cases. A short-term beneficial effect of mTOR inhibition on AML and total kidney volume was not reflected in improved renal function.

Tuberous sclerosis complex with autosomal dominant polycystic kidney disease: a rare duo

Tuberous sclerosis complex (TSC) is an autosomal dominant condition characterised by the presence of multiple hamartomas in various organ systems in the body. The kidneys are affected in 80% of patients, usually in the form of renal angiomyolipomas, renal cysts or renal cell carcinoma. Although extremely rare, TSC and autosomal dominant polycystic kidney disease (ADPKD) can co-exist in the same patient as a result of concurrent deletion of both polycystic kidney disease (PKD) 1 and TSC2 genes present on the chromosome 16p13.3. These patients develop end-stage renal disease at an earlier age and have an increased risk of malignancy. We present a case of a 30-year-old man with a history of tuberous sclerosis, presenting with loin pain and subsequently diagnosed to have ADPKD.

The classification of renal cystic diseases and other congenital malformations of the kidney and urinary tract

CONTEXT

Renal cystic diseases and congenital abnormalities of the kidney and urinary tract comprise a heterogeneous group of lesions whose pathogenesis has eluded physicians for centuries. Recent advances in molecular and genetic understanding of these diseases may provide the solution to this riddle.

OBJECTIVE

The formulation of an effective classification system for these disorders has been elusive but is needed to introduce order while providing a conceptual framework for diagnosis.

DATA SOURCES

This review discusses the evolution, beginning in the 19th century, of postulates regarding the pathogenesis of cystic and developmental renal diseases. Selected classification systems proffered during this period are discussed in pursuit of an ideal classification schema that would account for morphologic features and their clinical importance, with logical links to pathogenesis and treatment. Although this remains an elusive target, its general outline is becoming clearer. A classification approach favored by the author is presented, which incorporates many of the strengths contained in several previous classifications.

CONCLUSIONS

Genetic-and molecular-based postulates regarding the pathogenesis of the renal cystic and developmental diseases have implicated mutated master genes and the modification of genes that are crucial in renal development and genes that are central to the sensory effects of the renal tubular primary cilium on cell physiology. These scientific advances provide pathogenetic links between morphologically and genetically distinct entities and certain cystic and neoplastic entities, associations that seemed implausible not long ago. These advances may eventually provide the basis for future classification systems while suggesting targets for therapeutic approaches in the prevention and treatment of these diseases.

Renal cystic diseases and renal neoplasms: a mini-review

The past two decades have witnessed recognition of several new types of renal cell carcinoma, each with distinct cytogenetic abnormalities. Included are several genetic and acquired cystic kidney diseases associated with development of renal cell carcinoma, the topic of this review. The risk in patients with autosomal dominant polycystic kidney disease is not accurately known but may be slightly increased. The risk for patients with von Hippel-Lindau disease is substantial, and death from renal cancer is common. For patients with tuberous sclerosis complex, the challenge is recognition of the occasional malignancy arising in a field of many benign tumors. Patients with end-stage kidney disease and acquired cystic kidney disease may develop a variety of renal cell carcinoma types. Progress in understanding the molecular basis of renal cyst formation and neoplastic disease has fostered development of targeted therapies that now hold promise for a group of neoplasms whose cure was traditionally dependent on surgical approaches.

Characterization of large rearrangements in autosomal dominant polycystic kidney disease and the PKD1/TSC2 contiguous gene syndrome

Large DNA rearrangements account for about 8% of disease mutations and are more common in duplicated genomic regions, where they are difficult to detect. Autosomal dominant polycystic kidney disease (ADPKD) is caused by mutations in either PKD1 or PKD2. PKD1 is located in an intrachromosomally duplicated region. A tuberous sclerosis gene, TSC2, lies immediately adjacent to PKD1 and large deletions can result in the PKD1/TSC2 contiguous gene deletion syndrome. To rapidly identify large rearrangements, a multiplex ligation-dependent probe amplification assay was developed employing base-pair differences between PKD1 and the six pseudogenes to generate PKD1-specific probes. All changes in a set of 25 previously defined deletions in PKD1, PKD2 and PKD1/TSC2 were detected by this assay and we also found 14 new mutations at these loci. About 4% of the ADPKD patients in the CRISP study were found to have gross rearrangements, and these accounted for about a third of base-pair mutation negative families. Sensitivity of the assay showed that about 40% of PKD1/TSC contiguous gene deletion syndrome families contained mosaic cases. Characterization of a family found to be mosaic for a PKD1 deletion is discussed here to illustrate family risk and donor selection considerations. Our assay improves detection levels and the reliability of molecular testing of patients with ADPKD.

Tuberous Sclerosis Complex With Polycystic Kidney Disease of the Adult Type: the TSC2/ADPKD1 Contiguous Gene Syndrome

Although different diseases, tuberous sclerosis complex and autosomal dominant polycystic kidney disease have been seen in association, the molecular basis of this being the proximity of tuberous sclerosis complex 2 and polycystic kidney disease 1 genes on the same chromosome (16p13.3). Therefore, the classic autosomal dominant polycystic kidney disease renal phenotype may occur in the context of tuberous sclerosis complex disease as a result of large deletions involving both the polycystic kidney disease 1 and tuberous sclerosis complex 2 genes. This is known as the tuberous sclerosis complex 2/autosomal dominant polycystic kidney disease 1 contiguous gene syndrome. The criteria for this condition are fulfilled when renal lesions typical for classic autosomal dominant polycystic kidney disease phenotype are associated with tuberous sclerosis complex phenotype. We present a new case of the sporadic form of this genetic disorder. The diagnosis of tuberous sclerosis complex in this patient was established on the presence of major and minor features, and the diagnosis of ADPKD was based on the presence of numerous large roundish renal cysts lined by a nondescript tubular epithelium. Sporadic cases of autosomal dominant polycystic kidney disease and tuberous sclerosis complex do occur. Molecular analysis was not performed because the patient's parents refused permission.

Urological counseling and followup in pediatric tuberous sclerosis complex

PURPOSE

We review our experience with renal manifestations in pediatric patients with the tuberous sclerosis complex, and offer recommendations for urological counseling, followup and treatment of these patients.

MATERIALS AND METHODS

We reviewed clinical notes on 41 patients with the tuberous sclerosis complex followed at our institution from childhood. Patient data were gathered in a database focusing on renal involvement. The latter was assessed by periodic clinical evaluations and ultrasound. The risk of renal involvement was evaluated in relation to patient age, genotypic pattern and number of extrarenal manifestations.

RESULTS

Overall, 15 patients (36.6%) had renal involvement. The latter increased with age and was more common in cases with TSC2 genotypic pattern or multiple extrarenal manifestations. Angiomyolipomas were the most common lesions (11 patients), followed by renal cysts (2) and polycystic kidney disease (2). Cystic lesions were the most common in patients younger than 16 years. Renal failure developed in the 2 patients with polycystic kidney disease by the 2nd decade of life. Overall, treatment was required in 2 cases of symptomatic angiomyolipoma. Both patients were female, and had multiple extrarenal manifestations and bilateral renal involvement. One patient underwent open surgery at age 21.3 years and 1 underwent radiological embolization at age 23.4 years.

CONCLUSIONS

Pediatric patients with the tuberous sclerosis complex should undergo urological evaluation and followup. Although most of the lesions remain silent during childhood, the incidence of renal involvement increases with age. The need for treatment is highest in females with multiple extrarenal manifestations and bilateral renal involvement.

Gross genomic rearrangement involving the TSC2-PKD1 contiguous deletion syndrome: characterization of the deletion event by quantitative polymerase chain reaction deletion assay

Tuberous sclerosis complex (TSC) was instrumented for identification of the gene causing autosomal dominant polycystic kidney disease type 1 (PKD1) because a patient showing both diseases gave rise to the suggestion that the TSC2 gene is located in close vicinity on chromosome 16p13. However, distinct molecular genetic characterization of such patients is sparse in the literature. A 41-year-old woman was admitted because of chylous ascites and pleural effusions. She was on hemodialysis therapy for 6 years because of end-stage renal failure from PKD. Both kidneys had been removed at ages 35 and 36 years. Histologically, both specimens also showed multiple angioleiomyolipoma. Mild, but classic, lesions of the TSC complex were present on her face and hands and in the central nervous system. The genetic defect was identified by using quantitative real-time polymerase chain reaction (qPCR), long-range PCR (LR-PCR), and sequencing. qPCR confirmed the existence of a TSC2-PKD1 contiguous gene deletion spanning the entire TSC2 and PKD1 genes. Additional analysis showed expansion of the deletion affecting the adjacent downstream-located genes RAB26 and TRAF7, as well as the great majority of CASKIN1. LR-PCR and sequencing identified flanking simple tandem repeats. A nonhomologous misalignment mechanism has driven the recombination, most likely by replication slippage between a 3-bp homology (ATG) at the breakpoint regions. Our results confirm that patients with both TSC and PKD have a genetically contiguous gene syndrome with hemizygous deletion of the TSC2 and PKD1 genes. Despite this maximal genetic defect, the typical signs of TSC, mental retardation and seizures, can be absent.

[Renal manifestations in tuberous sclerosis]

BACKGROUND

Tuberous sclerosis is a rare inherited disease which can involve several organs. Renal involvement is one of the most severe manifestations of the disease. We analysed in this study renal involvement of tuberous sclerosis.

METHODS

We studied retrospectively nine cases of tuberous sclerosis with renal involvement diagnosed between 1994 and 2005. The diagnosis was based on the presence of typical extra-renal manifestations and familial history of tuberous sclerosis.

RESULTS

There were eight females and one male. Their mean age was 40.8+/-16.4 years (range: 15-62). At first presentation, we noted hypertension in three cases, proteinuria in seven cases, hematuria in eight cases and renal failure in five cases (end stage renal failure in four cases). By ultrasonography, we found angiomyolipoma in one case, cysts in four cases and angiomyolipoma associated to cysts in four cases. Nephrectomy was performed in two patients, in one case for hydronephrosis secondary to urolithiasis and in the other for hemorrhagic complication. In the later, pathological examination revealed renal carcinoma. At last evaluation, two patients were lost to follow-up, one had normal serum creatinine, five were on renal replacement therapy and the latter died from sepsis following kidney removal.

CONCLUSIONS

In our patients, renal disease was diagnosed late at chronic renal failure stage. Patients with end-stage renal failure require dialysis and renal transplantation, but we recommend binephrectomy after starting dialysis and before transplantation due to the risk of cancer and bleeding related to angiomyolipomas.

The tuberous sclerosis complex and its highly variable manifestations

PURPOSE

Tuberous sclerosis is an autosomal dominant neurocutaneous syndrome affecting multiple organ systems and demonstrating highly variable clinical manifestations. Mutations in 2 tumor suppressor genes, TSC1 and TSC2, are linked to the evolution of the hamartomatous lesions. We describe the incidence and epidemiology, variable clinical manifestations and their relationships to renal pathology, and the management of morbid sequelae.

MATERIALS AND METHODS

Using the search term tuberous sclerosis, we performed a MEDLINE search of the literature identifying 3,196 articles and selected those from urological, surgical, oncological, genetic and pediatric journals. Special focus was placed on the incidence and management of renal lesions and on different clinical manifestations and how they relate to renal tumors.

RESULTS

Due to improved identification of the variable phenotypic expression, the reported incidence has increased. TSC1 and TSC2 mutations are related to various phenotypic manifestations and risks of malignancy, such as an increased incidence of the TSC2 mutation in patients with renal cell carcinoma. Renal sparing surgery and selective embolization techniques have mitigated the morbidity of the lesions.

CONCLUSIONS

We now have a better understanding of the variability at the genotypic and phenotypic levels of the disease. We recommend that patients with tuberous sclerosis complex be evaluated by a multidisciplinary group of clinicians, including urologists, dermatologists, neurologists, pediatricians and geneticists. Close attention to these manifestations is necessary to ensure appropriate treatment of the sequelae of the tuberous sclerosis complex.

Molecular genetics and pathogenesis of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is a common and systemic disease characterized by formation of focal cysts. Of the three potential causes of cysts, downstream obstruction, compositional changes in extracellular matrix, and proliferation of partially dedifferentiated cells, evidence strongly supports the latter as the primary abnormality. In the vast majority of cases, the disease is caused by mutations in PKD1 or PKD2, and appears to be recessive at the cellular level. Somatic second hits in the normal allele of cells containing the germ line mutation initiate or accelerate formation of cysts. The intrinsically high frequency of somatic second hits in epithelia appears to be sufficient to explain the frequent occurrence of somatic second hits in the disease-causing genes. PKD1 and PKD2 encode a putative adhesive/ion channel regulatory protein and an ion channel, respectively. The two proteins interact directly in vitro. Their cellular and subcellular localization suggest that they may also function independently in a common signaling pathway that may involve the membrane skeleton and that links cell-cell and cell-matrix adhesion to the development of cell polarity.

Location of mutations within the PKD2 gene influences clinical outcome

BACKGROUND

Since the cloning of the gene for autosomal dominant polycystic kidney disease type 2 (PKD2), approximately 40 different mutations of that gene have been reported to be associated with the disease. The relationship between the PKD2 genotype and phenotype, however, remains unclear.

METHODS

Detailed clinical information was collected for PKD2 families in which the underlying mutation had been identified. Logistic regression analysis was employed to assess the influence of age and sex on hypertension, hematuria, renal calculi, and urinary tract infections, and a clinical phenotype score was computed. Patients were then grouped according to the relative location of their mutation within the cDNA sequence, and differences in the mean phenotypic score between groups were tested for statistical significance by means of a multiple pairwise t-test.

RESULTS

While phenotypic scores for each mutational group revealed a considerable degree of intragroup variability, the variability in phenotypic scores was significantly higher between mutational groups than within groups. A group-wise comparison of the mean phenotypic scores confirmed the observation of significant nonlinear variation in disease severity, with high- and low-scoring mutational groups interspersed along the gene sequence.

CONCLUSION

The identification of groups of mutations in the PKD2 gene, which differ significantly with respect to clinical outcome, is to our knowledge the first description of a genotype/phenotype correlation in autosomal dominant polycystic kidney disease. It also provides evidence against complete loss of function of the mutant PKD2 gene product.

Renal cystic disease

Renal cystic diseases constitute the most common genetic cause for end-stage renal disease in children and young adults. Recently, there has been rapid progress regarding the identification or chromosomal localization of some of the responsible disease genes. Studies of the respective gene products and of related animal models have led to new insights into the pathophysiology of these disorders. In this review, very recent developments are discussed as they pertain to molecular genetic diagnosis, the understanding of pathophysiology, and potential novel therapeutic approaches to renal cystic diseases.