Burkhard Tönshoff

TTC21B contributes both causal and modifying alleles across the ciliopathy spectrum

Ciliary dysfunction leads to a broad range of overlapping phenotypes, collectively termed ciliopathies. This grouping is underscored by genetic overlap, where causal genes can also contribute modifier alleles to clinically distinct disorders. Here we show that mutations in TTC21B, which encodes the retrograde intraflagellar transport protein IFT139, cause both isolated nephronophthisis and syndromic Jeune asphyxiating thoracic dystrophy. Moreover, although resequencing of TTC21B in a large, clinically diverse ciliopathy cohort and matched controls showed a similar frequency of rare changes, in vivo and in vitro evaluations showed a significant enrichment of pathogenic alleles in cases (P < 0.003), suggesting that TTC21B contributes pathogenic alleles to ∼5% of ciliopathy cases. Our data illustrate how genetic lesions can be both causally associated with diverse ciliopathies and interact in trans with other disease-causing genes and highlight how saturated resequencing followed by functional analysis of all variants informs the genetic architecture of inherited disorders.

Clinical presentation of genetically defined patients with hypokalemic salt-losing tubulopathies

PURPOSEnHypokalemic salt-losing tubulopathies (Bartter-like syndromes) comprise a set of clinically and genetically distinct inherited renal disorders. Mutations in four renal membrane proteins involved in electrolyte reabsorption have been identified in these disorders: the furosemide-sensitive sodium-potassium-chloride cotransporter NKCC2, the potassium channel ROMK, the chloride channel ClC-Kb, and the thiazide-sensitive sodium-chloride cotransporter NCCT. The aim of this study was to characterize the clinical features associated with each mutation in a large cohort of genetically defined patients.nnnPATIENTS AND METHODSnThe phenotypic characteristics of 65 patients with molecular defects in NKCC2, ROMK, ClC-Kb, or NCCT were collected retrospectively.nnnRESULTSnROMK and NKCC2 patients presented with polyhydramnios, nephrocalcinosis, and hypo- or isosthenuria. Hypokalemia was less severe in the ROMK patients compared with the NKCC2 patients. In contrast, NCCT patients had hypocalciuria, hypomagnesemia, and marked hypokalemia. While this dissociation of renal calcium and magnesium handling was also observed in some ClC-Kb patients, a few ClC-Kb patients presented with hypercalciuria and hypo- or isosthenuria.nnnCONCLUSIONSnROMK, NKCC2, and NCCT mutations usually have uniform clinical presentations, whereas mutations in ClC-Kb occasionally lead to phenotypic overlaps with the NCCT or, less commonly, with the ROMK/NKCC2 cohort. Based on these results, we propose an algorithm for the molecular diagnosis of hypokalemic salt-losing tubulopathies.

Decreased hepatic insulin-like growth factor (IGF)-I and increased IGF binding protein-1 and -2 gene expression in experimental uremia

The imbalance between normal insulin-like growth factor-I (IGF-I) and markedly increased IGF binding protein (IGFBP) plasma levels plays a pathogenic role for growth retardation and catabolism in children with chronic renal failure. To investigate the mechanism of these alterations, experiments were performed in an experimental model of uremia in rats (5/6 nephrectomy) and in pair-fed and ad libitum-fed sham-operated controls. Using a specific solution hybridization/RNase protection assay, we observed a marked reduction of hepatic IGF-I messenger RNA (mRNA) abundance at steady state in uremic animals (37 ± 5% of control) compared both with pair-fed (65 ± 10%) and ad libitum-fed controls (100± 11%) (P < 0.001). Reduced IGF-I gene expression was clearly organ-specific; it was most pronounced in liver (significant vs.. pair-fed controls) and lung and muscle tissue (significant vs.. ad libitum-fed controls); no change was observed in kidney and heart tissue. To determine a potential mechanism of reduced hepat...

The use of mycophenolate mofetil suspension in pediatric renal allograft recipients.

Abstract. Mycophenolate mofetil (MMF) is widely used to prevent acute rejection in adults after renal, cardiac, and liver transplantation. This study investigated the safety, tolerability, and pharmacokinetics of MMF suspension in pediatric renal allograft recipients. One hundred renal allograft recipients were enrolled into three age groups (33 patients, 3 months to <6 years; 34 patients, 6 to <12 years; 33 patients, 12 to 18 years). Patients received MMF 600 mg/m2 b.i.d. concomitantly with cyclosporine and corticosteroids with or without antilymphocyte antibody induction. One year after transplantation, patient and graft survival (including death) were 98% and 93%, respectively. Twenty-five patients (25%) experienced a biopsy-proven (Banff grade borderline or higher) or presumptive acute rejection within the first 6 months post-transplantation. Analysis of pharmacokinetic parameters for mycophenolic acid (MPA) and mycophenolic acid glucuronide showed no clinically significant differences among the age groups. The dosing regimen of MMF 600 mg/m2 b.i.d. achieved the targeted early post-transplantation MPA 12-h area under concentration-time curve (AUC0–12) of 27.2 µg h per ml. Adverse events had similar frequencies among the age groups (with the exception of diarrhea, leukopenia, sepsis, and anemia, which were more frequent in the <6 years age group) and led to withdrawal of MMF in about 10% of patients. Administration of MMF 600 mg/m2 b.i.d. is effective in prevention of acute rejection, provides predictable pharmacokinetics, and is associated with an acceptable safety profile in pediatric renal transplant recipients.

Web-based training: a new paradigm in computer-assisted instruction in medicine

Computer-assisted instruction (CAI) programs based on internet technologies, especially on the world wide web (WWW), provide new opportunities in medical education. The aim of this paper is to examine different aspects of such programs, which we call web-based training (WBT) programs, and to differentiate them from conventional CAI programs. First, we will distinguish five different interaction types: presentation; browsing; tutorial dialogue; drill and practice; and simulation. In contrast to conventional CAI, there are four architectural types of WBT programs: client-based; remote data and knowledge; distributed teaching; and server-based. We will discuss the implications of the different architectures for developing WBT software. WBT programs have to meet other requirements than conventional CAI programs. The most important tools and programming languages for developing WBT programs will be listed and assigned to the architecture types. For the future, we expect a trend from conventional CAI towards WBT programs.

Epidemiology and Morbidity of Epstein-Barr Virus Infection in Pediatric Renal Transplant Recipients: A Multicenter, Prospective Study

BACKGROUNDnThe epidemiology and morbidity of Epstein-Barr virus (EBV) infection in pediatric renal transplant recipients have been characterized insufficiently.nnnMETHODSnIn a prospective, multicenter study among 106 pediatric kidney allograft recipients aged 11.4 ± 5.9 years, we investigated the epidemiology of EBV infection and the relationship between EBV load, EBV serology, and EBV-related morbidity (posttransplant lymphoproliferative disease [PTLD] or symptomatic EBV infection, defined as flu-like symptoms or infectious mononucleosis).nnnRESULTSnEBV primary infection occurred in 27 of 43 (63%) seronegative patients and reactivation/reinfection in 28 of 63 (44%) seropositive patients. There was no association between the degree or duration of EBV load and EBV-related morbidity: The vast majority (17 of 18 [94%]) of patients with a high, persistent EBV load remained PTLD-free throughout a follow-up of 5.0 ± 1.3 years, while 2 of 3 (66%) patients with EBV-related PTLD exhibited only a low EBV load beforehand. Eight of 18 (44%) patients with a high, persistent EBV load remained asymptomatic during a follow-up of 5.3 ± 2.9 years. Multivariate analysis identified the EBV high-risk (D(+)/R(-)) serostatus (odds ratio [OR], 7.07; P < .05), the presence of human leukocyte antigen (HLA)-DR7 (OR, 5.65; P < .05), and the intensity of the immunosuppressive therapy (OR, 1.53; P < .01) as independent risk factors for the development of a symptomatic EBV infection.nnnCONCLUSIONSnPresence of EBV high-risk seroconstellation, HLA-DR7, and intensity of immunosuppressive therapy are significant risk factors for a symptomatic EBV infection, whereas there is no close association between the degree or duration of EBV load and EBV-related morbidity. Clinical Trials Registration.u2003NCT00963248.

Growth Hormone Treatment in Short Children with Chronic Kidney Disease

Growth hormone (GH) has been used for treatment of impaired growth in children with chronic kidney disease (CKD) for nearly 17 years. Controlled and open‐label studies have shown that GH is highly effective in improving growth velocity and adult height. The growth response is negatively correlated with age and height at start and time spent on dialysis treatment; it is positively correlated with dose and duration of treatment and the primary renal disease (renal hypodysplasia). In children with renal transplants, corticosteroid treatment is an additional factor negatively influencing spontaneous growth rates. However, GH treatment is able to compensate corticosteroid‐induced growth failure. GH treatment improved final height by 0.5–1.7 standard deviation score (SDS) in various studies, whereas the control group lost about 0.5 SDS in comparable time intervals. These variable results are explained in part by the factors mentioned above. The adverse events are comparable to those in non‐CKD children treated with GH.

Influence of growth hormone and insulin-like growth factor-I on kidney function and kidney growth

Decreased glomerular filtration rate (GFR) in hypopituitarism and increased GFR in acromegaly suggest that growth hormone (GH) has a substantial effect on renal haemodynamics. Extractive and recombinant human (rh) GH in healthy volunteers increased effective renal plasma flow (ERPF) and GFR by 10% and 15% respectively. Renal response to GH was delayed and occurred at the same time as an increase in plasma insulin-like growth factor (IGF)-I values, whereas infusion of rhIGF-I promptly increased GFR and ERPF, indicating that the haemodynamic response of the kidney to GH is mediated by IGF-I. In chronic renal failure (CRF), the acute effect of GH on GFR is obliterated. This might protect the diseased kidney against the undesired consequences of hyperfiltration. Indeed, rhGH treatment for 1 year in children with CRF did not lead to an accelerated decline in GFR compared with the year before treatment. GH and IGF-I also effect renal growth. Exposure to excessive GH in transgenic mice causes renomegaly and progressive glomerular selerosis. In acromegalic humans, increased renal size and weight and increased glomerular diameter are well known, whereas renal failure is not a long-term hazard. At least in normal and hypophysectomized rats treated with doses comparable with the therapeutic regimens used in stunted children, rhGH increased renal weight but in proportion to the increase in body weight indicating an isometric effect of GH on renal growth. From these data, major renal longterm side effects of rhGH treatment in children with CRF appear unlikely.

Prostanoids in paediatric kidney diseases.

Prostanoids belong to the growing family of eicosanoids, which are all derived from arachidonic acid. Prostanoids act as modulators and mediators in a large spectrum of physiological and pathophysiological processes within the kidney. On the one hand, the potent vasoconstrictor and platelet-aggregating thromboxane (TX) A2 is involved in the pathophysiology of a variety of glomerular diseases, such as haemolytic-uraemic syndrome and immune-mediated glomerulopathies. Prostaglandin (PG) E2, on the other hand, interferes with tubular electrolyte and water handling. Clinical data support the hypothesis that this member of the prostanoid family contributes to the pathophysiology of Bartters syndrome, hyperprostaglandin E syndrome, idiopathic hypercalciuria and renal diabetes insipidus. Both prostanoids, TXA2 and PGE2, are involved in the pathophysiology of obstructive uropathies. The physiological and protective role of renal vasodilator prostanoids (PGI2 and PGE2) has been studied during treatment with non-steroidal anti-inflammatory drugs. Part of the pharmacological effects of frusemide and converting enzyme inhibitors is mediated by PGI2 and PGE2. The role of renal prostanoids in cyclosporine toxicity is still equivocal. Future investigations on the physiological and pathophysiological role of renal prostanoids will have to consider the multiple interactions between prostanoids on the one hand, and classical hormones and other mediators (e. g. cytokines) on the other hand.

Effects of insulin-like growth factor I on the renal juxtamedullary microvasculature

To characterize the effects on the rat renal preglomerular microvasculature of insulin-like growth factor I (IGF-I), experiments were performed using the in vitro blood-perfused juxtamedullary nephron preparation. IGF-I induced a reversible vasodilation of pre- but not postglomerular microvessels in a dose-dependent manner (10-9-10-7M). The IGF-I-induced vasodilation was similar in all preglomerular vascular segments: interlobular artery, 11.5 ± 1.2% of control ( n = 16); mid-afferent arterioles, 11.6 ± 1.7% ( n = 24); and juxtaglomerular afferent segments, 16.1 ± 2.8% ( n = 19). Renal autoregulatory capacity was not reduced by IGF-I. Pretreatment with the nitric oxide (NO) synthase inhibitor N G-nitro-l-arginine methyl ester (10-4 M) completely inhibited the vasodilatory response to IGF-I. IGF-I induced a rapid increase of NO concentration in intact renal microvessels, monitored by a NO-selective voltametric microelectrode. Pretreatment with the cyclooxygenase inhibitor indomethacin (10-5 M) not only abrogated the IGF-I-induced dilation, but, moreover, IGF-I elicited a small but significant (∼10%) vasoconstriction in all preglomerular vessels. These results indicate that the renal vascular effects of IGF-I involve activation of two endogenous vasodilators (NO and vasodilatory prostaglandins). In addition, IGF-I may also release an undefined vasoconstrictor.