Background: Marcus Gunn syndrome is a rare congenital disorder. The major symptom is unilateral blepharoptosis during mandibular masticating movements and ptosis; although cases with the absence of the ptosis symptom in resting position, even rarer, were also recorded. The aim of this article was to present two cases of familial Marcus Gunn Jaw-Winking Synkinesis (MGJWS) without ptosis in two successive generations. Case Presentation: Upon routine examination, the 41-year-old female patient was diagnosed with MGJWS, with the synkinetic movement of the upper left eyelid only observed during the downward, forward, and lateral mandibular movements. Ptosis was not observed in the resting position. The patient’s 12-year-old daughter, who did not have any significant medical history, was also diagnosed with MGJWS, with the same symptoms. No surgical or conservative intervention was performed on the patients, and they are currently under regular follow-up. Conclusion: The absence of the ptosis symptom might make the diagnosis of MGJWS a challenge. The synkinetic movement being observed during masticatory movements presents a diagnostic opportunity for the dental clinician and surgeon since it will be observed during a routine temporomandibular joint examination. Thus, the authors think that it is important for dental clinicians and surgeons to be informed about the syndrome.

Keywords: Marcus Gunn (Jaw-Winking) Syndrome, Familial Marcus Gunn Phenomenon, Familial Marcus Gunn Jaw-Winking Synkinesis, Case Report, Maxillopalpebral Synkinesis, unilateral blepharoptosis, ptosis.