You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Disease"].

Please return the output as a JSON object of the format: {"Disease" : ["COVID-19", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Mapping the homolog of the human Rb1 gene to chromosome 14 of higher primates. The Rb1 gene has been implicated with retinoblastoma and is located on human Chromosome (Chr) 13q14. 2 2. A unique sequence human Rb1 cosmid DNA probe has been used to localize this region on apes Chr 14 by the FISH technique. The conservation of the Rb1 gene in higher primates at the corresponding equivalent chromosome locus (14q14) of the human may serve as a phylogenetic marker to further trace the evolutionary pathway of human descent.
{"Disease": ["retinoblastoma"]}