Cystinosis as a lysosomal storage disease with multiple mutant alleles: Phenotypic-genotypic correlations

Cystinosis is an autosomal recessive lysosomal storage dis-ease with an unclear enzymatic defect causing lysosomal cystine accumulation with no corresponding elevation of plasma cystine levels leading to multisystemic dysfunc-tion. The systemic manifestations include a proximal re-nal tubular defect （Fanconi-like）, endocrinal disturbances, eye involvements, with corneal, conjunctival and retinal depositions, and neurological manifestations in the form of brain and muscle dysfunction. Most of the long-term ill effects of cystinosis are observed particularly in pa-tients with long survival as a result of a renal transplant. Its responsible CTNS gene that encodes the lysosomal cystine carrier protein （cystinosin） has been mapped on the short arm of chromosome 17 （Ch17 p13）. There are three clinical forms based on the onset of main symp-toms： nephropathic infantile form, nephropathic juvenile form and non-nephropathic adult form with predominant ocular manifestations. Avoidance of eye damage from sun exposure, use of cystine chelators （cysteamine） and fnally renal transplantation are the main treatment lines. Pre-implantation genetic diagnosis for carrier parents is pivotal in the prevention of recurrence.

CTNS Molecular Genetics Profile in a Portuguese Cystinosis Population

Background: Cystinosis is a multisystemic autosomal recessive deficiency of the lysosomal membrane transporter protein (cystinosin) caused by mutations in CTNS gene. Objective: This study summarizes the Portuguese experience in the diagnosis and management of patients with this rare disease over the past few years and reports recurrent mutations in the CTNS gene. Methods: Unrelated patients from different pediatric and adult hospitals all over Portugal with non-nephrotic proteinuria, hypercalciuria, hypokalemia impaired proximal reabsorption of amino acids, glycosuria and hypophosphatemia, suggestive of a Fanconi syndrome and ocular problems, were studied. Intra-leukocyte cystine levels were determined and molecular analysis was performed, to determine the presence or absence of the 57-kb deletion in CTNS, followed by direct sequencing of the coding exons of CTNS. Results: From 1998 to 2017, twenty-one cystinotic patients were biochemically diagnosed. From the remaining seventeen (four deceased), eleven were studied for CTNS gene. Five out of eleven patients were homozygous for the 57-kb deletion (10/22;45.5%), and other five were compound heterozygous for this variant (15/22;68.2%). The other mutations found were p.Q128X (c.721 C>T;2/22), p.S139F (c.755 C>T;4/22) and c.18-21delGACT (p.T7FfsX7;1/22). All of these seventeen cystinotic patients are in treatment. Approximately 84% are adults, 16% are young children, and 54.5% are kidney transplant recipient. Conclusions: The authors would like to emphasize the importance of first screening for the 57-kb deletion since it is very common in our population. This genetic study is the first in our country and it could be the basis for future genetic counseling in Portuguese population.

Inherited Fanconi syndrome

Background Fanconi-Debré-de Toni syndrome(also known as Fanconi renotubular syndrome,or FRST)profoundly increased the understanding of the functions of the proximal convoluted tubule(PCT)and provided important insights into the pathophysiology of several kidney diseases and drug toxicities.Data sources We searched Pubmed and Scopus databases to find relevant articles about FRST.This review article focuses on the physiology of the PCT,as well as on the physiopathology of FRST in children,its diagnosis,and treatment.Results FRST encompasses a wide variety of inherited and acquired PCT alterations that lead to impairment of PCT reab-sorption.In children,FRST often presents as a secondary feature of systemic disorders that impair energy supply,such as Lowe's syndrome,Dent's disease,cystinosis,hereditary fructose intolerance,galactosemia,tyrosinemia,Alport syndrome,and Wilson's disease.Although rare,congenital causes of FRST greatly impact the morbidity and mortality of patients and impose diagnostic challenges.Furthermore,its treatment is diverse and considers the ability of the clinician to identify the correct etiology of the disease.Conclusion The early diagnosis and treatment of pediatric patients with FRST improve the prognosis and the quality of life.

Glomerular podocyte dysfunction in inherited renal tubular disease

Background Hereditary renal tubular disease can cause hypercalciuria,acid-base imbalance,hypokalemia,hypomagnesemia,rickets,kidney stones,etc.If these diseases are not diagnosed or treated in time,they can cause kidney damage and electrolyte disturbances,which can be detrimental to the maturation and development of the child.Glomerular involvement in renal tubular disease patients has only been considered recently.Methods We screened 71 papers(including experimental research,clinical research,etc.)about Dent's disease,Gitelman syndrome,and cystinosis from PubMed,and made reference.Results Glomerular disease was initially underestimated among the clinical signs of renal tubular disease or was treated merely as a consequence of the tubular damage.Renal tubular diseases affect glomerular podocytes through certain mechanisms resulting in functional damage,morphological changes,and glomerular lesions.Conclusions This article focuses on the progress of changes in glomerular podocyte function in Dent disease,Gitelman syndrome,and cystinosis for the purposes of facilitating clinically accurate diagnosis and scientific treatment and improving prognosis.