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HEREDITARY MONOGENIC DISEASES

           

Cystinosis

Prevalence is estimated at 1/200,000 individuals. Cystinosis is an autosomal recessive disease. The causative gene, CTNS, has 12 exons, is located on chromosome 17p13 and encodes the cystinosine protein.

Approximately 80 different mutations have been described in patients with variable clinical manifestation, these mutations have been detected in individuals of different geographical origins. The most frequent mutation is a 57 kb deletion detected in 60% or 70% of patients in northern Europe.

To date there are three clinical forms of cystinosis: infantile, juvenile and ocular, depending on the age of onset and severity of symptoms. Infantile is the most common and the first clinical signs appear after three months of age, with a polyuric-polydipsic syndrome and a marked delay in weight gain and height, secondary to the generalized alteration of the capacity of reabsorption of the proximal tubules (Toni-Debré-Fanconi syndrome), with severe electrolyte imbalance. Cystine deposits in several organs lead to hypothyroidism, insulin dependent diabetes, hepatosplenomegaly with portal hypertension, muscular and cerebral affectation. These patients also present ocular involvement, caused by cystine deposits in the cornea and conjunctiva, causing tearing and photophobia. The disease evolves progressively towards renal failure after 6 years of age.

The first symptoms of juvenile cystinosis typically appear around 8 years old, forming an intermediate clinical picture that leads to a terminal nephropathy after 15 years.

Finally, the ocular form is observed in adults, usually asymptomatic and may only present photophobia.

The diagnosis of cystinosis is confirmed by determining the cystine content in leukocytes. Can be performed prenatal diagnosis by genetic analysis in families with a previously affected child, or by measuring the incorporation of labeled 35S cystine in fibroblast cultures amniotic fluid samples or trophoblast cells.

Treatment involves the administration of electrolytes and vitamin supplements, indomethacin that improves overall condition and patient growth, and cysteamine, which decreases the concentration of intraleucocyte cystine, therefore, retards progression to renal failure.

The disease does not recur in renal transplantation.

GENE OR REGION STUDIED


  • CTNS