Damage to the left precentral gyrus is associated with Apraxia of speech (AOS) in acute to subacute stroke patients, suggesting a role of this brain region in motor speech production
((Itabashi R, Nishio Y, Kataoka Y, Yazawa Y, Furui E, Matsuda M, Mori E. Damage 
to the Left Precentral Gyrus Is Associated With Apraxia of Speech in Acute
Stroke. Stroke. 2016 Jan;47(1):31-6. doi: 10.1161/STROKEAHA.115.010402. Epub 2015
Dec 8. PubMed PMID: 26645260.
)).

A study supports the role of the left precentral gyrus in phonological output computation as well as seizure activity in a case of reading epilepsy
((Safi D, Béland R, Nguyen DK, Pouliot P, Mohamed IS, Vannasing P, Tremblay J,
Lassonde M, Gallagher A. Recruitment of the left precentral gyrus in reading
epilepsy: A multimodal neuroimaging study. Epilepsy Behav Case Rep. 2016 Jan
21;5:19-22. doi: 10.1016/j.ebcr.2016.01.003. eCollection 2016. PubMed PMID:
26909333; PubMed Central PMCID: PMC4744333.
)).

====Case reports====
A Japanese patient with pure agraphia displaying differential disturbances in processing Kanji (morphogram) and Kana (syllabogram) letters after an infarction in the middle and superior portions of the left precentral gyrus. Kana errors reflected the patient's difficulty with retrieving both motor and visual letter images, whereas Kanji errors included partial letter stroke omissions or additions. This present case suggests that differences in writing disturbances between Kana and Kanji letters are caused by a differential dependency on letter motor images
((Kurosaki Y, Hashimoto R, Tatsumi H, Hadano K. Pure agraphia after infarction
in the superior and middle portions of the left precentral gyrus: Dissociation
between Kanji and Kana. J Clin Neurosci. 2016 Apr;26:150-2. doi:
10.1016/j.jocn.2015.08.030. Epub 2015 Nov 17. PubMed PMID: 26597609.
)).