ROCKAWAY, N.J. -- Party City is closing 45 stores amid a global helium shortage, the company said in a statement to investors released Thursday.CEO James Harrison said the helium shortage "negatively impacted" its latex and metallic balloon categories.However, Harrison said, the New Jersey-based company has signed a letter of agreement for a new source of helium that would provide a new supply beginning this summer."We believe this new source should substantially eliminate the shortfall we are experiencing at current allocation rates and improve our ability to return to a normal level of latex and metallic balloon sales," Harrison said.Party City plans to close the 45 stores this year. It currently has 870 locations.The company did not disclose which stores would be shuttered.Harrison said Party City typically closes 10 to 15 stores per year in response to market conditions.Party City posted more information about the helium shortage on its website.