The IL-2RG R328X nonsense mutation allows partial STAT-5 phosphorylation and defines a critical region involved in the leaky-SCID phenotype.

In addition to their detection in typical X-linked severe combined immunodeficiency, hypomorphic mutations in the interleukin (IL)-2 receptor common gamma chain gene (IL2RG) have been described in patients with atypical clinical and immunological phenotypes. In this leaky clinical phenotype the diagnosis is often delayed, limiting prompt therapy in these patients. Here, we report the biochemical and functional characterization of a nonsense mutation in exon 8 (p.R328X) of IL2RG in two siblings: a 4-year-old boy with lethal Epstein-Barr virus-related lymphoma and his asymptomatic 8-month-old brother with a Tlow B+ natural killer (NK)+ immunophenotype, dysgammaglobulinemia, abnormal lymphocyte proliferation and reduced levels of T cell receptor excision circles. After confirming normal IL-2RG expression (CD132) on T lymphocytes, signal transducer and activator of transcription-1 (STAT-5) phosphorylation was examined to evaluate the functionality of the common gamma chain (γc ), which showed partially preserved function. Co-immunoprecipitation experiments were performed to assess the interaction capacity of the R328X mutant with Janus kinase (JAK)3, concluding that R328X impairs JAK3 binding to γc . Here, we describe how the R328X mutation in IL-2RG may allow partial phosphorylation of STAT-5 through a JAK3-independent pathway. We identified a region of three amino acids in the γc intracellular domain that may be critical for receptor stabilization and allow this alternative signaling. Identification of the functional consequences of pathogenic IL2RG variants at the cellular level is important to enable clearer understanding of partial defects leading to leaky phenotypes.

Complement factor 5 (C5) p.A252T mutation is prevalent in, but not restricted to, sub-Saharan Africa: implications for the susceptibility to meningococcal disease.

Complement C5 deficiency (C5D) is a rare primary immunodeficiency associated with recurrent infections, particularly meningitis, by Neisseria species. To date, studies to elucidate the molecular basis of hereditary C5D have included fewer than 40 families, and most C5 mutations (13 of 17) have been found in single families. However, the recently described C5 p.A252T mutation is reported to be associated with approximately 7% of meningococcal disease cases in South Africa. This finding raises the question of whether the mutation may be prevalent in other parts of Africa or other continental regions. The aim of this study was to investigate the prevalence of C5 p.A252T in Africa and other regions and discuss the implications for prophylaxis against meningococcal disease. In total, 2710 samples from healthy donors within various populations worldwide were analysed by quantitative polymerase chain reaction (qPCR) assay to detect the C5 p.A252T mutation. Eleven samples were found to be heterozygous for p.A252T, and nine of these samples were from sub-Saharan African populations (allele frequency 0·94%). Interestingly, two other heterozygous samples were from individuals in populations outside Africa (Israel and Pakistan). These findings, together with data from genomic variation databases, indicate a 0·5-2% prevalence of the C5 p.A252T mutation in heterozygosity in sub-Saharan Africa. Therefore, this mutation may have a relevant role in meningococcal disease susceptibility in this geographical area.

[Aluminum and uremic bone disease. Diagnostic utility of serum aluminum and the deferoxamine (DFO) test ]. / Aluminio y enfermedad ósea urémica. Utilidad diagnóstica del aluminio sérico y del test de la deferoxamina (DFO).

The optimal control of aluminium content in dialysis fluids has resulted in a decrease in the incidence of aluminium related bone disease (ARBD) and in the risk for aluminium toxicity. Nevertheless the problem has not disappeared. Bone biopsy with specific staining for Al remains the only reliable method for the diagnosis of ARBD. Currently there is not a total agreement on the reliability of serum Al levels and of the DFO test in the identification of patients with Al overload or toxicity. In a series of patients (mean age 48 +/- 14 years old) from our hemodialysis units we carried out bone biopsy and we studied the prevalence of bone aluminium overload and of ARBD and the usefulness of serum aluminium and of DFO test in their diagnosis. Seventy- three bone biopsies were evaluated by histomorphometric analysis and aluminium staining (Aluminon). Al overload was diagnosed when the Aluminon staining was positive independent of the bone surface covered with Al and of the bone formation rate (BFR). Patients were consider to have ARBD when aluminium covered > 25% of bone surface and BFR was < 0.031 micron 3/micron 2/day. Fifteen patients had aluminium overload while 7 patients were considered to have ARBD. Positive Aluminon staining appeared in all histopathological forms of renal osteodystrophy although it appeared mainly in patients with mixed lesion and osteomalacia. Most of the patients with adynamic bone disease had negative Aluminon staining. Patients with aluminium overload showed lower bone formation and mineralization rates. Serum aluminium levels below 40 micrograms/l were useful to exclude bone aluminium overload. Serum aluminium levels and DFO test were not specific in diagnosing aluminium overload or ARBD. A DFO test with an increment in serum aluminium over 100 micrograms/l in combination with a serum PTH below 200 pg/ml was useful to diagnose ARBD.

[Study of renal osteodystrophy by bone biopsy. Age as an independent factor. Diagnostic value of bone remodeling markers]. / Estudio de la osteodistrofia renal mediante biopsia ósea. La edad como factor independiente. Utilidad diagnóstica de los marcadores del remodelado óseo.

The spectrum of bone disease in uremic patients on hemodialysis has changed in the last years. Undecalcified bone biopsy with histomorphometric measurements and tetracycline labelling remains the gold standard for diagnosis of the different forms of renal osteodystrophy. But because of its invasive nature and complicated laboratory processing a number of non-invasive biochemical parameters have been proposed. The aim of our study was to determine the prevalence of the different forms of renal osteodystrophy in our patients in hemodialysis. Moreover we analyse the correlation between several biochemical parameters and the histological findings and evaluate their diagnostic and predictive value. Transiliac bone biopsies were performed in seventy three uremic patients (31 males) on chronic hemodialysis and static and dynamic parameters were measured. Serum levels of intact parathyroid hormone (iPTH), osteocalcin (OC), total alkaline phosphatase (FAT) and bone alkaline phosphatase (FAO) were determined. High-bone remodelling (50 pts, 68.5%) predominates over low-bone remodelling (23 pts, 31.5%). The distribution of the different types of bone disease was: Mild hyperparathyroidism 8 pts, Osteitis fibrosa 37 pts, Mixed lesions 5 pts, Adynamic bone disease 21 pts and Osteomalacia 2 pts. Six of our 73 patients were diabetics and they had adynamic bone disease (4 pts), osteomalacia (1 pt) and osteitis fibrosa (1 pt). Patients older than 50 years presented lower cellular activity (osteoblast surface, ObS/BS) and lower bone formation rate (BFR/BS). iPTH showed different correlation with these parameters of bone formation in patients above and below 50 years old suggesting that older patients need higher levels of PTH to obtain a determined level of bone formation. iPTH, OC, FAT and FAO correlated with the majority of histomorphometric indices of bone formation and resorption, though the best correlations were those with iPTH. The diagnostic and predictive value of these bone markers is better with high-bone remodelling. Serum levels of FAT > 300 U/l, OC > 150 ng/ml, FAO > 40 ng/ml and iPTH > 200 pg/ml showed a positive predictive value of 1 (with a specificity of 1, but sensibility below 0.78 except for iPTH that is 0.95) in the diagnosis of high-bone remodelling. After an analysis with ROC curves the cut-off value to differentiate high from low-bone remodelling was obtained. iPTH level > 200 pg/ml combined with one of the other markers (FAT > 150 U/l, FAO > 30 ng/ml or OC > 100 ng/ml) are predictive of high-bone remodelling, while values below those figures are predictive of low-bone remodelling.

Different patterns of renal osteodystrophy in Iberoamerica.

The various forms of renal osteodystrophy are predominant hyperparathyroid bone disease, mixed uremic osteodystrophy, low turnover osteomalacia, and adynamic bone disease. The present study analyses a total number of 1,209 bone biopsies from 5 different countries (Brazil, Uruguay, Argentina, Portugal, and Spain). Low turnover osteomalacia and mixed uremic osteodystrophy were more common in Brazil, Uruguay, and Argentina than in Portugal and Spain whereas predominant hyperparathyroid bone disease was seen more often in Portugal and Spain. In all centers, independent of the aluminum staining technique used, the extent of aluminum deposited in bone was greater in patients presenting with low bone turnover, whether from low turnover osteomalacia or adynamic bone disease, than in the predominant hyperparathyroid bone disease. In summary, even though recent reports have indicated that, over the last decade, the incidence of aluminum-induced toxicity was reduced, aluminum still seems to be implicated in a great percentage of symptomatic low bone remodelling lesions in Iberoamerica.

Estudio de la osteodistrofia renal mediante biopsia ósea. La edad como factor independiente. Utilidad diagnóstica de los marcadores del remodelado óseo / Study of renal osteodystrophy by bone biopsy. Age as an independent factor. Diagnostic value of bone remodelling markers

La biopsia ósea sin decalcificar y su estudio histomorfométrico son esenciales para el diagnóstico exacto de las alteraciones óseas en el paciente urémico. Actualmente disponemos de una serie de marcadores bioquímicos del remodelado óseo que pueden ser de utilidad en el estudio y seguimiento de la osteodistrofia renal. Nos propusimos estudiar mediante biopsia ósea la prevalencia de los diferentes tipos histológicos, buscar factores relacionados con su desarrollo, relacionar los marcadores bioquímicos con los diferentes parámetros histomorfométricos y analizar su capacidad diagnóstica. Se biopsiaron 73 pacientes. Se realizó estudio histomorfométrico estático y dinámico. Se determinó PTHi, osteocalcina, fosfatasa alcalina total y la fracción ósea. Hubo un predominio de alto remodelado (enfermedad leve 10,9 por ciento, osteítis fibrosa 50,6 por ciento y enfermedad mixta 6,8 por ciento) sobre el bajo remodelado (enfermedad adinámica 28 por ciento y osteomalacia 2,7 por ciento). Los enfermos con enfermedad leve y adinámica fueron más frecuentemente mujeres. La mayoría de los enfermos diabéticos presentaron enfermedad adinámica. Los pacientes de mayor edad presentaron menor actividad celular y tasa de remodelado óseo. La PTHi, osteocalcina, fosfatasa alcalina total y ósea se mostraron como buenos marcadores del remodelado óseo presentando buenas correlaciones con la mayoría de los parámetros tanto de formación como de resorción. La PTHi fue el índice que mejores correlaciones presentó y mejor diferenció los grupos histológicos entre sí. Con un nivel de corte de PTHi en 200 pg/ml más otro marcador (fosfatasa alcalina total 150 U/l; fosfatasa alcalina ósea 30 nglml; osteocalcina 100 ng/ml) se consiguió diferenciar el alto del bajo remodelado (AU)

[Effects of dietary phosphorus restriction on the production of 1,25(OH)2D3 (calcitriol) in patients with moderated renal failure]. / Efectos de una restricción de fósforo dietético en la producción de 1,25(OH)2D3 (calcitriol) en pacientes con insuficiencia renal moderada.

UNLABELLED: Calcitriol deficiency and phosphate retention are two main factors in the pathogenesis of renal hyperparathyroidism. In spite of normal serum levels, phosphate may have an important role even in moderate RI. The aim of this study was to evaluate the effect of dietary phosphorus restriction on serum levels of calcitriol in patients with moderate RI. We studied 21 patients (7 F/14 M); mean age 61.7 +/- 15 years old; corrected creatinine clearance 51.4 +/- 14 ml/m. Serum PTH, calcitriol 25(OH)D3, calcium, phosphorus and urinary excretion of calcium and phosphorus were measured before and after 30 days on phosphorus restricted diet (700 mg/day). RESULTS: [table: see text] CONCLUSIONS: Our patients with moderate RI have elevated serum levels of PTH while calcitriol was in the lower normal range. Dietary phosphorus restriction resulted in a significant decrease in PTH levels and a significant increase in serum calcitriol concentrations. The levels of 25(OH)D3 did not change in this study.

Efectos de una restricción de fósforo dietético en la producción de 1,25(OH)2D3 (calcitriol) en pacientes con insuficiencia renal moderada / Calcitriol levels in moderate renal insufficiency (RI) after dietary phosphorus restriction

El déficit de calcitriol y la retención de fósforo son dos mecanismos fundamentales en la patogenia del hiperparatiroidismo renal. En la insuficiencia renal (IR) moderada el papel del fósforo parece significativo a pesar de encontrarse en niveles séricos normales. El objetivo de este estudio fue evaluar el efecto sobre los niveles de calcitriol de una restricción de fósforo en la dieta, en pacientes con IR moderada. Se seleccionaron 25 pacientes y completaron el estudio 21 (7 mujeres y 14 hombres), con edad media de 61,7 ñ 15 años. El filtrado glomerular corregido (FG) fue de 51,4 ñ 14 ml/m. Realizaron una dieta con restricción del fósforo (aproximadamente 700 mg/día) durante 30 días. Fueron analizados los niveles de 1,25(OH)2D3 (calcitriol), de hormona paratiroidea intacta (PTH), de 25(OH)D3, calcio, fósforo, creatinina, urea y albúmina séricas. Igualmente se determinaron el cociente calcio/creatinina y fósforo/creatinina urinarios y la reabsorción tubular de fosfato (RTP).Se obtuvieron los siguientes resultados tras la dieta: los niveles de PTH descendieron significativamente (81,3 ñ 35 frente a 71 ñ 39 pg/ml, p < 0,05); los niveles de calcitriol se elevaron significativamente (22,4 ñ 4,4 frente a 33,4 ñ 7,5 pg/ml; los niveles de 25(OH)D3 no sufrieron variación significativa; se obtuvo una correlación significativa entre los valores basales de calcitriol y los obtenidos tras finalizar la dieta (r = 0,49; p < 0,05).Nuestros pacientes con IR moderada presentan valores elevados de PTH y valores de calcitriol en el rango inferior de la normalidad. La dieta baja en fósforo elevó los niveles de calcitriol de forma marcada y descendió los niveles de PTH, sin llegar al rango normal. Los niveles superiores de calcitriol conseguidos en IR moderada con un fácil cambio en la dieta, pueden ser útiles en la prevención del hiperparatiroidismo secundario y probablemente de otros trastornos presentes en la IR (AU)

Bone alkaline phosphatase isoenzyme in renal osteodystrophy.

Serum total alkaline phosphatase is the most commonly used biochemical marker of bone disease in renal patients, but alkaline phosphatase originates from different organs and sometimes lacks specificity. Bone isoenzyme measurement is considered superior to total alkaline phosphatase for the assessment of bone metabolism. We have studied the value of bone isoenzyme, determined by a new. IRMA (Tandem-R-Ostase), in haemodialysis patients with secondary hyperparathyroidism and renal osteodystrophy. Fifty-six haemodialysis patients were studied. Intact parathyroid hormone (PTH), osteocalcin, total alkaline phosphatase and bone alkaline phosphatase were determined. A transiliac bone biopsy was performed in 20 of the 56 patients after double tetracycline labelling. There was a significant correlation between bone alkaline phosphatase and PTH (r = 0.79, P < 0.001) and between bone and total alkaline phosphatase (r = 0.84, P < 0.001) in all patients. The patients who underwent a bone biopsy showed osteitis fibrosa in 17, mixed lesion in one, adynamic bone disease in one and normal bone in one. Bone alkaline phosphatase showed a significant correlation with static and dynamic histomorphometric indices similar to that obtained with PTH and better than those of total alkaline phosphatase and osteocalcin. It is concluded that bone alkaline phosphatase (ostase) seems to be a useful non-invasive marker of bone metabolism in patients on haemodialysis with high turnover bone disease. More studies are necessary to know its value in low turnover bone disease.