T. Martin Barratt

Incompletely penetrant PKD1 alleles suggest a role for gene dosage in cyst initiation in polycystic kidney disease.

Autosomal dominant polycystic kidney disease (ADPKD) caused by mutations in PKD1 is significantly more severe than PKD2. Typically, ADPKD presents in adulthood but is rarely diagnosed in utero with enlarged, echogenic kidneys. Somatic mutations are thought crucial for cyst development, but gene dosage is also important since animal models with hypomorphic alleles develop cysts, but are viable as homozygotes. We screened for mutations in PKD1 and PKD2 in two consanguineous families and found PKD1 missense variants predicted to be pathogenic. In one family, two siblings homozygous for R3277C developed end stage renal disease at ages 75 and 62 years, while six heterozygotes had few cysts. In the other family, the father and two children with moderate to severe disease were homozygous for N3188S. In both families homozygous disease was associated with small cysts of relatively uniform size while marked cyst heterogeneity is typical of ADPKD. In another family, one patient diagnosed in childhood was found to be a compound heterozygote for the PKD1 variants R3105W and R2765C. All three families had evidence of developmental defects of the collecting system. Three additional ADPKD families with in utero onset had a truncating mutation in trans with either R3277C or R2765C. These cases suggest the presence of incompletely penetrant PKD1 alleles. The alleles alone may result in mild cystic disease; two such alleles cause typical to severe disease; and, in combination with an inactivating allele, are associated with early onset disease. Our study indicates that the dosage of functional PKD1 protein may be critical for cyst initiation.

IgA IMMUNE COMPLEXES IN HENOCH-SCHÖNLEIN PURPURA

Raised levels of IgA immune complexes were found in 13 of 18 children with Henoch-Schönlein purpura irrespective of whether they developed nephritis or not. In contrast, only those children who developed nephritis had raised levels of IgG immune complexes as well. In 2 children with nephritis, two discrete peaks of IgA complexes were found, corresponding to 4 x 10(5) to 8 x 10(5) and 2.5 x 10(6) to 4 x 10(6) daltons. IgG complexes were found only in the larger-molecular-weight peak. Such differences in immune complexes may underlie the different manifestations of this disease.

The polymorphonuclear leucocyte count in childhood haemolytic uraemic syndrome

Review of data from 79 children with the haemolytic uraemic syndrome (HUS) showed that the polymorphonuclear leucocyte (PMN) count at presentation in childhood HUS predicts outcome. Logistic regression analysis of several features at presentation identified only the PMN count and the presence of a diarrhoeal prodrome as having a significant effect on the outcome (P<0.01 andP<0.001 respectively). The geometric mean PMN count was significantly raised in 70 children who had typical HUS following a diarrhoeal prodrome (D+cases) compared with that of 9 children who had atypical disease without diarrhoea (D-cases) (t-test on log-transformed data,P<0.005). Fifty-seven children with D+HUS who recovered completely had a significantly lower geometric mean PMN count than D+cases with a bad outcome (P<0.001). Four of these patients, who died in the acute stage of the disease, had a significantly higher mean count than the rest of the D+patients (P<0.001). Multiple regression analysis demonstrated that the PMN count in D+cases was not significantly influenced by haemoglobin concentration, platelet count, length of the prodrome, or the administration of antibiotics in the prodromal period. A high PMN count at presentation in D+HUS indicates a poor prognosis. The data emphasise the heterogeneity of HUS and suggest that PMN participate in the pathogenesis of the disorder in typical D + cases but not in atypical D- cases.

Long-term cyclosporin A treatment of minimal-change nephrotic syndrome of childhood

We evaluated the efficacy of long-term cyclosporin A (CyA) treatment in the maintenance of remission in 40 children with steroid-dependent minimal-change nephrotic syndrome (MCNS). CyA was given in an initial dose of 5 mg/kg per day, adjusted to maintain a trough whole blood level of 50–150 ng/ml. All the 40 children received CyA for 1 year. In 18 patients, CyA was continued for a further period of at least a year without interruption; 9 patients had a second course of CyA therapy after an interval of at least 1 month. Of the 40 children 29 (72%) had one or more relapses during treatment with CyA, with 16 (40%) relapsing during the 1st year. During the second period of CyA, 10 (56%) of the 18 children treated continuously relapsed, whereas all the 9 children who had an interrupted course of therapy relapsed. CyA was discontinued at one time in 27 patients, all of whom subsequently relapsed, with a median time to relapse of 26 days. Long-term prednisolone in addition to CyA was required to maintain remission in 16 (40%) of the whole group. The results suggest that the long-term use of CyA is able to maintain remission of MCNS, although 40% of the patients also required low-dose alternate-day steroids; patients appeared to fare worse if the CyA course was interrupted; no patient experienced a long-term remission after CyA was stopped.

Crescentic glomerulonephritis in children

Data on patients with crescentic glomerulonephritis (>50% glomeruli with crescents), referred to the Hospital for Sick Children during the past 13 years, were reviewed. Thirty patients (13 male, 17 female) aged 3.7–15.7 years (mean 9.5) were evaluated. Initial clinical features included: oedema (24/30), hypertension (19/30), gross haematuria (15/30), oliguria (15/30) and a decreased glomerular filtration rate (GFR<30 ml/min per 1.73 m2) (22/30). Henoch-Schönlein purpura was present in 9 patients, microscopic polyarteritis in 3, polyarteritis nodosa in 1, Wegeners granulomatosis in 1, systemic lupus erythematosus in 1, post-streptococcal glomerulonephritis in 2, mesangiocapillary glomerulonephritis in 7, anti-glomerular basement membrane glomerulonephritis in 2, and 4 were idiopathic. In 10 patients 50%–79% of glomeruli were affected by crescentic changes (group 1) and in the remaining 20, 80% or more (group 2). The crescents were cellular, fibrocellular or fibrous, and the degree of sclerosis was assessed. Patients in both groups were treated with plasma exchange, corticosteroids, anticoagulants, cyclophosphamide and azathioprine in different combinations. On follow-up, 3 patients were dead, 1 was lost to follow-up, 12 were on dialysis/transplant programmes, 4 had a GFR of less than 30 and 10 a GFR of more than 30 ml/min per 1.73 m2. In our experience, 50% progressed to end-stage renal failure. The interval between disease onset and start of treatment was a prognostic factor for outcome. Fibrous crescents were associated with a worse outcome than fibrocellular crescents (P<0.05). Outcome was not, however, related to the percentage of glomeruli affected (P>0.05). Although the effectiveness of the individual components of the treatment regimens used was difficult to assess, one-third of patients at the latest follow-up had a GFR of more than 30 ml/min per 1.73 m2.

Neutrophil activation in the haemolytic uraemic syndrome: free and complexed elastase in plasma

There is evidence of neutrophil involvement in the pathogenesis of the haemolytic uraemic syndrome (HUS), and neutrophil release products are thought to cause endothelial cell damage. Elastase is the major lysosmal proteinase liberated by activated neutrophils. In this study we measured both free and complexed elastase. No free elastase activity could be detected in the plasma of patients with diarrhoea-associated (D+) HUS using a specific substrate. However, there was a marked increase in α1-antitrypsin (α1-AT) complexed elastase as measured by a newly developed enzyme-linked immunosorbent assay not only in D+ HUS, but also in non-diarrhoea-associated (D-) HUS. This finding is independent of either a high polymorphonuclear leucocyte count or renal failure. This increase in bound elastase together with our sequential data which demonstrate raised α1-AT complexed elastase levels early in the disease process further support the theory that neutrophil activation is one of the key events in the pathophysiology of this disorder.

Lymphocyte subpopulations, interleukin-2 and interleukin-2 receptor expression in childhood nephrotic syndrome.

Abnormal T lymphocyte function and reduced interleukin-2 (IL-2) production have been implicated in the pathogenesis of the nephrotic syndrome (NS). We investigated: (1) lymphocyte subpopulations and expression of IL-2 receptor (IL-2R) on T cells using two-colour flow cytometry, (2) serum IL-2 and (3) the soluble component of IL-2R (sIL-2R) in serum, using enzyme-linked immunosorbent assay, in 38 children with NS. All children, except those in remission, had marked proteinuria. They were divided into groups according to renal pathology: (1) steroid-sensitive NS (SSNS) not receiving prednisolone therapy, (2) SSNS on prednisolone, (3) focal segmental glomerulosclerosis (FSGS), (4) SSNS in remission and not receiving prednisolone therapy, (5) congenital NS (CNS). Results were compared with 26 age-matched controls. Total T lymphocytes (CD3) were reduced in groups 1 and 2; CD4 count was reduced in groups 1–4; CD8 count increased in groups 2 and 3; CD8 and CD19 (B lymphocytes) were significantly reduced in group 5. Increased IL-2R expression (CD25) on CD4 lymphocytes was noted in groups 1, 2 and 3 implying activation of these cells. In patients with SSNS, increased serum sIL-2R was recorded during relapse (1,273±497 U/l vs. 913±401 U/l in remission,P<0.005) but free serum IL-2 was not detectable at any stage. The specific alterations in lymphocyte subpopulations in SSNS and FSGS would imply an involvement of the immune system distinct from that in CNS.

Variability of urine albumin excretion in normal and diabetic children

The variability of urine albumin excretion (UAE) was studied in normal and diabetic children and, in addition, the best method of expressing the data was investigated. In 39 timed overnight urine samples from diabetic children, the urine albumin creatinine clearance ratio (CA/CC) was compared with the urine albumin creatinine concentration ratio (UA/UC), the urine albumin excretion rate (UAER) and the urine albumin concentration (UA). UA/UC predicted CA/CC (r=0.95) better than either UAER (r=0.83,P<0.02) or UA (r=0.90), 0.1>P>0.05). The within-individual and the between-individual variability in overnight UA/UC in 171 urine samples from 73 normal children was compared with that of 406 urine samples from 119 diabetic children, using a “random effects type 2 nested analysis of variance” model. Geometric mean (range) UA/UC (mg/mmol) in diabetic children, 0.55 (0.04–6.90), was greater than in normal children, 0.33 (0.05–2.10,P<0.01), and 18% of diabetics had a value of UA/UC above the normal range. Within-individual variance was the same in normals (0.12) and diabetics (0.12), but between-individual variance in diabetics (0.18) was much greater than in normals (0.03). These data show that within-individual observations for both normals and diabetics are highly but equally variable. Furthermore, from these data, it is possible to infer that a minimum of five estimations are necessary per individual to estimate the true mean value of urine albumin excretion with reasonable confidence.

Fanconi syndrome, ichthyosis, dysmorphism, jaundice and diarrhoea — a new syndrome

We describe six infants, from consanguineous marriages, with a new syndrome comprising the Fanconi syndrome, ichthyosis, musculoskeletal abnormalities, jaundice and diarrhoea. In addition two of the infants were found to have abnormal platelet morphology — the grey platelet syndrome. No evidence of a recognised metabolic disorder was found in any of the six infants, nor did they appear to be typical of any previously described syndromes. Their progress was poor: they required high fluid and bicarbonate intakes and all died by the age of 6 months of dehydration, acidosis and sepsis.

Clomerular and urinary heparan sulphate in congenital nephrotic syndrome

Studies using cationic probes have suggested that a reduction in glomerular anionic sites, composed principally of the glycosaminoglycan heparan sulphate, is responsible for the abnormal glomerular permeability in the congenital nephrotic syndrome (CNS). We therefore analysed the glycosaminoglycan content of the glomerular basement membrane (GBM) from an infant who died of CNS and from an infant who died of unrelated causes. We also measured the urinary excretion of glycosaminoglycans in children with nephrotic syndrome, both congenital and acquired, and in healthy children. Heparan sulphate constituted 59% of the glycosaminoglycan content of the GBM in the normal infant, the other principal glycosaminoglycan being chondroitin sulphate. In the GBM from the infant with CNS the heparan sulphate was greatly reduced, constituting only 3% of total glycosaminoglycans. The urinary excretion of heparan sulphate was significantly increased in CNS (expressed both in relation to creatinine and to chondroitin sulphate) compared with normal children and to those with acquired nephrotic syndrome. Diminished GBM content of heparan sulphate may be responsible for the abnormal glomerular permeability in CNS and may be a consequence of defective incorporation of heparan sulphate into the GBM with subsequent loss into the urine.