Renal involvement in tuberous sclerosis complex and von Hippel-Lindau disease: shared disease mechanisms?

Tuberous sclerosis complex exhibits a new renal cystogenic mechanism

Tuberous sclerosis complex (TSC) is a tumor predisposition syndrome with significant renal cystic and solid tumor disease. While the most common renal tumor in TSC, the angiomyolipoma, exhibits a loss of heterozygosity associated with disease, we have discovered that the renal cystic epithelium is composed of type A intercalated cells that have an intact Tsc gene that have been induced to exhibit Tsc-mutant disease phenotype. This mechanism appears to be different than that for ADPKD. The murine models described here closely resemble the human disease and both appear to be mTORC1 inhibitor responsive. The induction signaling driving cystogenesis may be mediated by extracellular vesicle trafficking.

Outcomes of angioembolization and nephrectomy for renal angiomyolipoma associated with tuberous sclerosis complex: a real-world US national study

OBJECTIVE

To examine outcomes of clinical procedures for renal angiomyolipoma associated with tuberous sclerosis complex (TSC) based on US national health claims databases.

METHODS

This retrospective cohort study selected two cohorts of TSC patients, who underwent either embolization or nephrectomy (either partial or complete) for renal angiomyolipoma in the years from 2000 through 2011. Based on claims diagnosis codes, we estimated the prevalence rates of 10 angiomyolipoma-related conditions and 50 embolization- or nephrectomy-related conditions in the pre- and post-baseline periods respectively, and made cross-year and cross-period comparison of these rates with repeated measures analysis methods.

RESULTS

The embolization cohort (N = 4280) and the nephrectomy cohort (N = 3842) had mean baseline ages of 50.7 and 51.7 years with 52.5% and 51.3% males, respectively. After the intervention, the embolization cohort had statistically significant reductions (all p < .05) in gross hematuria (-27.7%), retroperitoneal hemorrhage (-8.4%), and abdominal mass (-6.9%), and increases in hypertension (15.5%), renal mass or unspecified disorder of kidney and ureter (13.8%), anemia (5.1%), and renal insufficiency (3.3%). Similarly, the nephrectomy cohort saw statistically significant reductions (all p < .05) in gross hematuria (-30.6%), flank pain (-7.5%), and abdominal mass (-6.4%), but increases in hypertension (11.9%), renal insufficiency (10.4%), and anemia (7.6%). Embolization was associated with post-procedure increases in renal mass or unspecified kidney/ureter disorder (13.9%), other disorders of kidney and ureter (3.4%), non-acute renal insufficiency (3.1%), flank pain (3.7%), renal insufficiency (3.2%), etc. (all p < .05). Nephrectomy was associated with post-procedure increases in postoperative ileus (5.3%), pain and headache (4.8%), paralytic ileus (3.6%), etc. (all p < .05).

CONCLUSIONS

Both embolization and nephrectomy were effective, but associated with increases in certain angiomyolipoma-related conditions. Further, the embolization effect on gross hematuria, retroperitoneal hemorrhage, and abdominal mass might subside after the intervention year.

Angiomyolipoma have common mutations in TSC2 but no other common genetic events

Renal angiomyolipoma are part of the PEComa family of neoplasms, and occur both in association with Tuberous Sclerosis Complex (TSC) and independent of that disorder. Previous studies on the molecular genetic alterations that occur in angiomyolipoma are very limited. We evaluated 9 angiomyolipoma for which frozen tissue was available from a consecutive surgical series. Seven of 8 samples subjected to RT-PCR-cDNA sequencing showed mutations in TSC2; none showed mutations in TSC1 or RHEB. Six of the seven mutations were deletions. We searched for 983 activating and inactivating mutations in 115 genes, and found none in these tumors. Similarly analysis for genomic regions of loss or gain, assessed by Affymetrix SNP6.0 analysis, showed no abnormalities. Loss of heterozygosity in the TSC2 region was commonly seen, except in patients with low frequency TSC2 mutations. We conclude that sporadic renal angiomyolipoma usually have mutations in TSC2, but not TSC1 or RHEB, and have no other common genomic events, among those we searched for. However, chromosomal translocations and gene fusion events were not assessed here. TSC2 inactivation by mutation is a consistent and likely necessary genetic event in the pathogenesis of most angiomyolipoma.

Burden of disease and unmet needs in tuberous sclerosis complex with neurological manifestations: systematic review

OBJECTIVES

Tuberous sclerosis complex (TSC) is a progressive genetic disorder characterized by pervasive benign tumor growth. We sought to assess the current understanding of burden of TSC-related neurological manifestations.

METHODS

We systematically searched MEDLINE- and EMBASE-indexed, English-language literature (5/2000-5/2010) and non-indexed materials.

RESULTS

In total, 119 articles were included, 115 on epidemiology and treatment. Recent prevalence estimates from Ireland and Taiwan report TSC in 1:14,000-25,000 individuals, below older estimates of 1:10,000. While neurological manifestations are common, treatment is largely unaddressed by guidelines and focuses on symptoms, with resection standard for subependymal giant cell astrocytomas (SEGAs) and common practice for refractory epilepsy. Antiepileptic drugs and mammalian target of rapamycin inhibitors safely, effectively minimize the need for surgery for severe epilepsy and SEGAs.

CONCLUSION

Morbidity and treatment burden of prevalent neurological manifestations is significant, suggesting substantial economic and humanistic burden; however, these areas are poorly studied, indicating total disease burden is unknown. Future research should assess quality of life, caregiver burden, and costs.

Clinical and molecular description of a Wilms tumor in a patient with tuberous sclerosis complex

We report on a girl affected with tuberous sclerosis, carrying a germline de novo TSC2 mutation, c.4934-4935delTT, leading to a p.F1645CfsX7, who developed a unilateral Wilms tumor (WT). Molecular investigation of the tumor biopsy at diagnosis revealed the loss of the constitutional wild-type TSC2 allele, and loss of heterozygosity for the WT1 gene. Deletion of the WTX gene was also present, but it involved the functionally inactive X chromosome. No mutation affecting the remaining WT1 and WTX alleles, as well as the CTNNB1 gene was found. Pathological examination of the surgical specimen documented the presence of diffuse anaplasia and p53 immunoreactivity. To the best of our knowledge, this is the second report of a patient with tuberous sclerosis who developed a WT, and it represents the first case in which a detailed clinical and molecular description is provided.

Diagnosis and management of childhood polycystic kidney disease

A number of syndromic disorders have renal cysts as a component of their phenotypes. These disorders can generally be distinguished from autosomal dominant polycystic kidney disease (ADPKD) and autosomal recessive polycystic kidney disease (ARPKD) by imaging studies of their characteristic, predominantly non-renal associated abnormalities. Therefore, a major distinction in the differential diagnosis of enlarge echogenic kidneys is delineating ARPKD from ADPKD. ADPKD and ARPKD can be diagnosed by imaging the kidney with ultrasound, computed tomography, or magnetic resonance imaging (MRI), although ultrasound is still the method of choice for diagnosis in utero and in young children due to ease of use, cost, and safety. Differences in ultrasound characteristics, the presence or absence of associated extrarenal abnormalities, and the screening of the parents >40 years of age usually allow the clinician to make an accurate diagnosis. Early diagnosis of ADPKD and ARPKD affords the opportunity for maximal anticipatory care (i.e. blood pressure control) and in the not-too-distant future, the opportunity to benefit from new therapies currently being developed. If results are equivocal, genetic testing is available for both ARPKD and ADPKD. Specialized centers are now offering preimplantation genetic diagnosis and in vitro fertilization for parents who have previously had a child with ARPKD. For ADPKD patients, a number of therapeutic interventions are currently in clinical trial and may soon be available.

Loss of primary cilia upregulates renal hypertrophic signaling and promotes cystogenesis

Primary cilia dysfunction alters renal tubular cell proliferation and differentiation and associates with accelerated cyst formation in polycystic kidney disease. However, the mechanism leading from primary ciliary dysfunction to renal cyst formation is unknown. We hypothesize that primary cilia prevent renal cyst formation by suppressing pathologic tubular cell hypertrophy and proliferation. Unilateral nephrectomy initiates tubular cell hypertrophy and proliferation in the contralateral kidney and provides a tool to examine primary cilia regulation of renal hypertrophy. Conditional knockout of the primary cilia ift88 gene leads to delayed, adult-onset renal cystic disease, which provides a window of opportunity to conduct unilateral nephrectomy and examine downstream kinetics of renal hypertrophy and cyst formation. In wild-type animals, unilateral nephrectomy activated the mTOR pathway and produced appropriate structural and functional hypertrophy without renal cyst formation. However, in ift88 conditional knockout animals, unilateral nephrectomy triggered increased renal hypertrophy and accelerated renal cyst formation, leading to renal dysfunction. mTOR signaling also increased compared with wild-type animals, suggesting a mechanistic cascade starting with primary ciliary dysfunction, leading to excessive mTOR signaling and renal hypertrophic signaling and culminating in cyst formation. These data suggest that events initiating hypertrophic signaling, such as structural or functional loss of renal mass, may accelerate progression of adult polycystic kidney disease toward end-stage renal disease.

Glomerulocystic kidney disease

Glomerulocystic disease is a rare renal cystic disease with a long descriptive history. Findings from recent studies have significantly advanced the pathophysiological understanding of the disease processes leading to this peculiar phenotype. Many genetic syndromes associated with glomerulocystic disease have had their respective proteins localized to primary cilia or centrosomes. Transcriptional control of renal developmental pathways is dysregulated in obstructive diseases that also lead to glomerulocystic disease, emphasizing the importance of transcriptional choreography between renal development and renal cystic disease.

Diagnosis and screening of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited cause of kidney failure and accounts for approximately 5% of ESRD population in the United States. The disorder is characterized by the focal and sporadic development of renal cysts, which increase in size and number with age. Mutations of PKD1 and PKD2 account for most of the cases. Although the clinical manifestations of both gene types overlap completely, PKD1 is associated with more severe disease than PKD2, with larger kidneys and earlier onset of ESRD. In general, renal ultrasonography is commonly used for the diagnosis of ADPKD, and age-dependent criteria have been defined for subjects at risk of PKD1. However, the utility of the PKD1 ultrasound criteria in the clinic setting is unclear because their performance characteristics have not been defined for the milder PKD2 and the gene type for most test subjects is unknown. Recently, highly predictive ultrasound diagnostic criteria have been derived for at-risk subjects of unknown gene type. Additionally, both DNA linkage or gene-based direct sequencing are now available for the diagnosis of ADPKD, especially in subjects with equivocal imaging results, subjects with a negative or indeterminate family history, or in younger at-risk individuals being evaluated as potential living-related kidney donors. Here, we review the clinical utilities and limitations of both imaging- and molecular-based diagnostic tests and outline our approach for the evaluation of individuals suspected to have ADPKD.