Kystins

Kystins are a group of rare, inherited metabolic disorders characterized by the accumulation of cystine, a sulfur-containing amino acid, within lysosomes due to defects in the cystine transport protein. These conditions primarily affect the kidneys, eyes, brain, and other organs, leading to a range of clinical manifestations depending on the specific type and severity of the disorder.

The most well-known kystinosis is **nephropathic cystinosis**, also referred to as **type 1 cystinosis**, which is the most severe form. It typically presents in early infancy with symptoms such as polyuria, polydipsia, growth failure, and metabolic acidosis. Over time, untreated nephropathic cystinosis can progress to chronic kidney disease, requiring dialysis or transplantation. Additional features may include muscle weakness, hypothyroidism, and retinal degeneration. Without treatment, the prognosis is often poor, with many affected individuals succumbing to kidney failure in childhood.

Other forms of cystinosis include **intermediate cystinosis** and **ocular cystinosis**, which are generally milder. Intermediate cystinosis presents with later-onset kidney disease and fewer systemic symptoms, while ocular cystinosis primarily affects the eyes, leading to vision impairment due to cystine crystal accumulation in the cornea and retina.

Diagnosis of kystinosis is confirmed through genetic testing or measurement of cystine levels in white blood cells or other tissues. Treatment typically involves the use of **cysteamine**, an amino acid derivative that chelates cystine, reducing its accumulation in cells. Regular monitoring of kidney function, electrolyte balance, and other organ systems is essential for managing the condition. Bone marrow transplantation has been explored as a potential curative therapy but is not widely available.

Kystinosis is inherited in an autosomal recessive manner, meaning an individual must inherit two copies of the defective gene (one from each parent) to develop the disorder. Genetic counseling is recommended for families with a history of cystinosis to assess the risk of recurrence. Research continues to improve understanding and treatment options for these rare but debilitating conditions.