How many genes does the human hoxD cluster contain?
['Both children are heterozygous for a deletion that eliminates at least eight (HOXD3-HOXD13) of the nine genes in the HOXD cluster']
["The human HOXD complex contains nine genes: HOXD1, HOXD3, HOXD4, HOXD8, HOXD9, HOXD10, HOXD11, HOXD12 and HOXD13, which are clustered from 3′ to 5′ in an approximately 100-kb stretch on chromosome 2q31.1 with HOXD1 at the 3' end and HOXD13 the 5′ end."]
['9']