The UN body dedicated to protect and help the refugees all around the world is the UNHCR - except for the Palestinian refugees who are the sole group to have their own, specially dedicated UN body: the UNWRA. No other group has such. Also, definition of refugee used by UNWRA is broader than the one used by UNHCR and they also have a different mandate (UNHCR is to help integrate the refugees in their current country which means that there is no "right to return" principle for any other group of refugees except for Palestinians)
From the wiki page of UNWRA:
"UNRWA is the only agency dedicated to helping refugees from a specific region or conflict and is separate from UNHCR. Formed in 1950, UNHCR is the UN main Refugee Agency, which is responsible for aiding other refugees all over the world. UNHCR, unlike UNRWA, has a specific mandate to aid its refugees to eliminate their refugee status by local integration in current country, resettlement in a third country or repatriation when possible. UNRWA allows refugee status to be inherited by descendants."
Why are the Paletinian "refugees" treated so specially?
("" is because the vast majority of them wouldn't be counted as refugees according to the Geneva Convention used to define who is a refugee in the case of any other group)