% ▁carry ▁none ▁of ▁these ▁mut ations . ▁These ▁mut ations ▁are ▁not ▁specific ▁to ▁my el of ib ros is , ▁and ▁are ▁linked ▁to ▁other ▁my el op rol ifer ative ▁ne op las ms , ▁specifically ▁poly cy th emia ▁ver a ▁and ▁essential ▁th rom b oc yth emia . ▁ ▁The ▁V 6 1 7 F ▁mut ation ▁to ▁the ▁J AK 2 ▁protein ▁is ▁found ▁in ▁approximately ▁half ▁of ▁individuals ▁with ▁primary ▁my el of ib ros is . ▁The ▁V 6 1 7 F ▁mut ation ▁is ▁a ▁change ▁of ▁val ine ▁to ▁phen yl al an ine ▁at ▁the ▁ 6 1 7 ▁position . ▁Jan us ▁kin ases ▁( J AK s ) ▁are ▁non - re ceptor ▁ty ros ine ▁kin ases ▁essential ▁for ▁the ▁activation ▁of ▁signal ing ▁that ▁is ▁medi ated ▁by ▁cy tok ine ▁re cept ors ▁lack ing ▁catal yt ic ▁activity . ▁These ▁include ▁re cept ors ▁for ▁er yth ro po iet in , ▁th rom b opo iet in , ▁most ▁inter le uk ins ▁and ▁inter fer on . ▁J AK 2 ▁mut ations ▁are ▁significant ▁because ▁J AK 2 ▁plays ▁a ▁role ▁in ▁cont rolling ▁production ▁of ▁blood ▁cells ▁from ▁h emat opo iet ic ▁stem ▁cells . ▁The ▁V 6 1 7 F ▁mut ation ▁appears ▁to ▁make ▁h emat opo iet ic ▁cells ▁more ▁sensitive ▁to ▁growth ▁factors ▁that ▁need ▁J AK 2 ▁for ▁signal ▁trans du ction , ▁which ▁include ▁er