NEW YORK (TheStreet) -- Shares of Spark Therapeutics (ONCE - Get Report) were gaining, up 5.82% to $71.06 in late morning trading Thursday, after company co-founder and CEO Jeff Marrazzo appeared on Jim Cramer's Mad Money show on CNBC last night.

TheStreet's Jim Cramer, Portfolio Manager of the Action Alerts PLUS Charitable Trust Portfolio said, "This is a very exciting story. Spark uses gene therapy to address major unmet medical needs."

"They're developing one-time treatments that can basically cure, cure, patients with debilitating genetic diseases," Cramer continued.

Marrazzo explained that gene therapy helps correct the underlying causes of certain diseases by delivering the necessary genes to the cells that are missing it or improperly producing it.

Spark's first drug targets the RPE65 gene that causes blindness in some children, and has been showing miraculous results.

Spark is also exploring treatments for hemophilia and other diseases, and Cramer says this company is "capable of doing amazing things."

Philadelphia, Penn.-based Spark Therapeutics is engaged in developing products in the field of gene therapy.

Spark's product candidate, SPK-RPE65, which is in Phase III clinical trial stage, targets a group of rare blinding conditions known as inherited retinal dystrophies caused by non-sex linked or autosomal recessive mutations in the RPE65 gene.

Spark is also developing various follow-on product candidates targeting other IRDs, including SPK-CHM for the treatment of choroideremia.

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