Paul A. Tomlinson

Differential excretion of urinary proteins in children with vesicoureteric reflux and reflux nephropathy.

We studied 40 children with a history of vesicoureteric reflux (VUR) without evidence of renal scarring, 93 children with a history of VUR and renal scarring and 10 children with previous urinary tract infections in whom the urinary tract was radiologically normal. Urine retinol-binding protein (RBP), albumin andN-acetyl-β-d-glucosaminidase (NAG) were measured in each child. All were free from infection at the time of the analysis. Urinary RBP and NAG levels were significantly elevated (P<0.001) in the group of children with renal scarring. Elevated RBP levels were detected in 51% of children with bilateral renal scarring compared with 7% of children with unilateral scarring. Urine RBP excretion increased progressively according to the type of scarring, best determined by the type of scarring of the less affected kidney. In children with renal scarring, elevated NAG levels were seen mostly in the 65 children with bilateral scarring and severe reflux. Urine albumin excretion was elevated in 10 children, 9 with bilateral scarring, all of whom had elevated RBP excretion. Urine protein excretion was unaffected by the presence or absence of persisting VUR. There was a strong negative correlation between glomerular filtration rate and RBP excretion (r=−0.69). We conclude that evidence of tubular dysfunction is common in children with bilateral renal scarring and usually precedes any glomerular protein leak. Tubular dysfunction may be the consequence of relative nephron hyperperfusion in the presence of bilateral scarring.

Low molecular weight proteins in children with renal disease

Low molecular weight proteins are of interest in children because their increased urinary excretion is a sign of renal tubular disease and their increased plasma concentration is inversely related to glomerular filtration rate. These proteins include β2-microglobulin (B2M), retinolbinding protein (RBP), α1-microgloulin (A1M) and lysozyme. B2M is unstable in acid urine, in contrast to RBP and A1M which are more stable. Any increase in the urinary excretion of B2M or RBP is highly specific for tubular disease, whereas increased excretion of A1M may be seen with glomerular proteinuria. Areas of clinical application include tubular and glomerular diseases, detection of drug toxicity, reflux nephropathy, birth asphyxia and insulin-dependent diabetes mellitus. Methods of sample collection and analysis of these proteins are discussed.

Measurement of β2-microglobulin, retinol-binding protein, α1-microglobulin and urine protein 1 in healthy children using enzyme-linked immunosorbent assay

Enzyme-linked immunosorbent assays (ELISA) have been developed for the measurement of β2-microglobulin (B2M), retinol-binding protein (RBP), α1-microglobulin (A1M) and urine protein 1 (UP1) in children. Results from random urine samples in 43 children (31 for B2M) are, when corrected for urine creatinine (geometric mean (range)): B2M 9.8 (6.0–40.7) μg/mmol, RBP 8.1 (< 1–24.5) μg/mmol, A1M 0.4 (0.1–2.2) mg/mmol and UP1 17.8 (< 2–309.4) μg/mmol. Fractional excretions (FE) in 23 children (14 for B2M) are (geometric mean (range)): FEB2M 0.04% (0.02–0.10%) and FEUP1 0.10% (0.01–1.21%). Results in overnight urine collections are also presented. Our results extend existing data for normal ranges in adults to include children and provide data on UP1 concentrations.

Low molecular weight protein excretion in glomerular disease: a comparative analysis.

Abstract. We studied 23 children with steroid-sensitive nephrotic syndrome (SSNS), 21 children with steroid-resistant types of nephrotic syndrome and 32 children with other types of nephritis. Our controls were 43 apparently healthy children. We measured the urinary excretion of N-acetyl-β-D-glucosaminidase (NAG) and the low molecular weight (LMW) proteins β2-microglobulin (B2M), retinol-binding protein (RBP), α1-microglobulin (A1M) and urine protein 1 (UP1). Results for B2M were considered only for a urine pH greater than 6.0. Comparisons were made with urine albumin excretion, glomerular filtration rate (GFR) and tubular abnormalities in selected renal biopsy samples. We found that abnormalities of LMW protein excretion occurred in between 50% (B2M) and 88% (UP1) of all subjects. In children with SSNS, A1M (r = 0.73), UP1 (r = 0.65) and NAG (r = 0.54) excretion were significantly correlated with albumin excretion, but not RBP or B2M excretion. Increased fractional excretion of A1M, B2M and UP1 and increased plasma A1M were demonstrated in 9 children with SSNS, suggesting competition for tubular reabsorption with albumin, most marked for UP1. In the steroid-resistant nephrotic and nephritic syndromes, correlation with albumin was found for all proteins. In these subjects, RBP (r = 0.37), B2M (r = 0.42) and A1M (r = 0.28) were inversely correlated with GFR, but not UP1, NAG or albumin. We found that RBP excretion was significantly greater in the presence of severe tubular abnormalities in 11 children with recent renal biopsies, but not A1M, UP1 or NAG. We conclude that LMW proteinuria is common in children with glomerular disease, and does not necessarily imply a poor prognosis. Factors other than histologically proven tubular abnormality may account for elevated LMW protein excretion. RBP is the LMW protein most closely associated with structural abnormality and least affected by increasing albuminuria.

Frequency and genetic spectrum of maturity-onset diabetes of the young (MODY) in southern New Zealand

Maturity-Onset Diabetes of the Young (MODY) is a monogenic form of diabetes, consisting of a heterogeneous group of autosomal dominant inherited disorders. Typical onset is in individuals prior to twenty five years, and presentation can mimic type 1 or 2 diabetes. Molecular genetic testing can allow precise identification of the different MODY sub-types. Making a specific diagnosis of MODY can have important implications for the guidance of appropriate treatment, prognosis and genetic counselling.We present the cases of three children and their families diagnosed with MODY over the past two years. These families highlight the features of three of the more common MODY subtypes, including two with novel mutations, one of which segregates in a kindred that is strongly affected by both MODY and classic autoimmune mediated diabetes. To date, we have identified a prevalence of MODY in the paediatric diabetes population of the lower South Island, New Zealand, of approximately 2.5%. This prevalence, along with increasing access to molecular genetic testing, highlights the importance of consideration of MODY in atypical diabetes presentations in the paediatric/adolescent population.

Baller-Gerold syndrome associated with congenital portal venous malformation.

We report a 4 year old boy in whom the clinical features of craniosynostosis and bilateral absent radii led to a diagnosis of Baller-Gerold syndrome. Additional congenital abnormalities included midface hypoplasia, atrial and ventricular septal defects, right hydronephrosis, partial sacral agenesis, and anterior ectopic anus. Evidence of portal venous hypertension was present from 8 months and a congenital portal venous malformation was discovered at 2 years. This is the first reported case of Baller-Gerold syndrome associated with a congenital portal venous malformation. We discuss the diagnostic confusion between this syndrome and other overlapping malformation syndromes and propose optimal evaluation strategies aimed at clarifying the nosology of these syndromes.

Urinary proteins in vesicoureteric reflux: when the same thinking leads to different conclusions

On reading the paper by Tomlinson et al. [1] in the first 1994 issue of Pediatric Nephrology we were pleased with the conclusion that analysing tubular proteinuria in children with vesicoureteric reflux (VUR) may add something to the clinical picture of these patients. This has been the final conclusion of a previous paper by our group published in the same journal [2]. Despite this, there were some differences between the two studies. It should be stressed, however, that the two papers are in full agreement on many points and, in our view, the central message is the same. A major finding of our study was that 43 of 82 patients with VUR had augmented levels of retinol-binding protein (RBP) in urine; of this group 28 had a reduced glomerular filtration rate (GFR) and in these patients an effect of tubular overload on the urinary levels of the protein was hypothesised. The same finding was reported by Tomlinson et al. [1] in a larger population of children with VUR, but the proportion of patients with VUR without scarring and high urinary levels of RBP was lower than in our original report (3/40 compared with 4/23). In these patients, we found a twofold increase in urinary RBP or [32-microglobulin compared with the upper limits of a normal population of 91 school children [2]. Comparable normal limits were subsequently obtained in a larger population of 365 children [3] who had mean RBP urinary levels of 40 ~tg/g creatinine (range 1-150 gg/g), the maximal level corresponding to 18 on the scale utilised by Tomlinson et al. [1] (gg/mmol creatinine). Owing to the very large number of children studied, we believe our range effectively represents the normal limits for urinary RBP in an Italian paediatric population. Another difference between the two studies concerns the correlation found by Tomlinson et al. [1] between urinary RBP and renal scarring in patients with both normal and decreased GFR. We too observed a good correlation between urinary levels of RBP and degree of scarring when considering the whole population (i.e. normal and low GFR). However, we excluded patients with low GFR, since other mechanisms of tubular proteinuria may be operating in those patients. In summary, we think that the differences between the two studies are only artifactual, while the basic conclusions are the same, and indicate the usefulness of urinary RBP determination in patients with VUR. Long-term follow-up studies should more clearly indicate the real value of urinary RBP as a marker of incipient renal disease.

Spectrum of MODY in the south of New Zealand - including two novel mutations

Maturity Onset Diabetes of the Young (MODY) is a monogenic form of diabetes. It consists of a heterogeneous group of autosomal dominant inherited disorders, with typical onset in individuals aged less than twenty five years. There are several different sub-types of MODY which can be precisely identified using molecular genetic testing. Modes of presentation vary and can mimic type 1 or 2 diabetes. Making a specific diagnosis of MODY can have important implications for guidance of appropriate treatment, prognosis and genetic counselling. The paediatric diabetes team across the Southern District Health Board provides diabetes care to approximately 160 children and adolescents spread over the largest geographical region in New Zealand. We present the cases of three children and their families diagnosed with MODY over the past two years. This includes two novel mutations, one of which segregates in a unique kindred that is strongly affected by both MODY and classic autoimmune mediated diabetes. These families highlight the features of three of the more common MODY subtypes; MODY2 - a 13 year old boy with a novel unclassified variant c.698G>A (p.Cys233Tyr) in exon 7 of the Glucokinase (GCK) gene, MODY5 – a 14 year old girl with a novel de novo dosage change of a 1.3MB deletion in the HNF1β gene, and MODY3 with a reported nonsense mutation c.864delGinsCC (p.Gly282ArgfsX25) in exon 4 of the HNF1α gene observed in an 11 year old girl. In addition to these index cases, genetic testing has lead to the diabetes diagnosis of a sibling with a GCK mutation, and the identification of an HNF1α mutation in another currently asymptomatic sibling. To date, we have identified a prevalence of MODY in the paediatric diabetes population of the lower South Island of approximately 2.5%. This prevalence, along with increasing access to molecular genetic testing, highlights the importance of consideration of MODY in atypical diabetes presentations in the paediatric/adolescent population.