Cystinosis (MIM 219800, 219900 and 219750) is a rare autosomal recessive disorder affecting 1/175,000 individuals. The condition is caused by the failure to transport the amino acid cysteine out of the lysosomes. Cystine (a dimer of two cysteine molecules) accumulates forming crystals which causes cell and tissue destruction in all systems of the body. Excess cystine can be detected by cystine binding protein assays which can be used to confirm a clinical diagnosis. Three forms of cystinosis have been defined by age of onset and severity of symptoms. The most common form is infantile nephropathic cystinosis (95% of cases) that has an age of onset of 6-12 months. Features include renal proximal tubular dysfunction (renal Fanconi syndrome), without treatment affected children suffer worsening growth retardation and develop end stage renal failure by ~10 years. The juvenile form of cystinosis occurs in around 4-5% of affected individuals. Age of onset is between 12-15 years and individuals usually present with proteinuria and glomerular renal impairment, but do not suffer from such profound tubular dysfunction or growth retardation. The benign form of cystinosis occurs in adulthood, individuals do not suffer from any renal disease and grow normally. They require no treatment and have a normal life expectancy and quality, except perhaps for photophobia due to cystine crystals in the cornea.
Also known as
Infantile nephropathic cystinosis
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Clinically affected patients should have their diagnosis confirmed by biochemical analysis; this should be arranged either locally or with the Enzyme Unit, Great Ormond Street Hospital. Biochemical confirmed patients can be referred for mutation analysis. The CTNS gene consists of 12 exons. The most common mutation is a 57kb deletion which is found in ~76% of northern Europeans and makes up one third of all mutations found in individuals with cystinosis. The rest of the mutations reported are spread throughout the coding area of the gene and include insertions, small deletions, nonsense, splicing and missense mutations. No mutation hotspots have been identified. Level 1 Mutation Analysis: Testing for the common 57kb deletion by PCR analysis. Level 2 Mutation Analysis: Direct sequencing of exons 3 to 12 of the CTNS gene (exons 1 & 2 are non-coding).
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Great Ormond Street Hospital NE Thames Regional Genetics Service Laboratories
Great Ormond Street Hospital for Children
37 Queen Square
1ml EDTA neonates, 5ml EDTA adults
Common mutation - 10 days; gene screen - 40 days
Disease / group
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Prenatals must be arranged in advance, through a Clinical Genetics department if possible. Amniotic fluid or CV samples should be sent to Cytogenetics for dissecting and culturing, with instructions to forward the sample to the Regional Molecular Genetics laboratory for analysis