What Your Test Results Mean:

Carriers typically show no symptoms of cystinosis; however, carriers are at an increased risk of having a child with cystinosis. Risk for the current or future pregnancies is dependent on your partner’s carrier status. Carrier testing of your partner is recommended in addition to consultation with a genetic counselor.

Disease Explained:

Cystinosis is an inherited condition that prevents the body from breaking down the amino acid cysteine. Beginning in infancy, the accumulated cysteine forms crystals that cause damage to the body’s organs, especially the kidneys and eyes. When the kidneys are damaged in this way they eliminate important nutrients from the body, causing the affected child to have poor growth and soft bones. Cystinosis can eventually cause the kidneys to fail and cysteine crystal formation in the eyes makes them extremely sensitive to light (photophobia). Cystinosis is a treatable disease: a drug called cysteamine reduces the crystallization of cysteine in the body’s tissues. Kidney transplant is often required. Untreated cystinosis severely reduces life expectancy for affected individuals, but proper medical treatment can allow them to live into their 50s. For unexplained reasons, some people with cystinosis do not develop symptoms until adolescence, while others develop only photophobia with no kidney involvement.

How the Genetics Works:

Cystinosis is an autosomal recessive disorder caused by pathogenic variants in the CTNS gene. In general, individuals have two copies of the CTNS gene. Carriers of cystinosis have a single variant in one copy of the CTNS gene while individuals with cystinosis have variants in both copies of their genes, one inherited from each parent. Risk for two carriers to have a child with the disorder is 25%.