Unilateral, bilateral symmetric or asymmetric isolated hearing loss in patients with heterozygous KITLG variants

KITLG pathogenic variants have been associated to three distinct clinical presentations with different combinations of hearing loss and/or pigmentation abnormalities. However, its involvement in isolated hearing loss has not been confirmed since its initial description in two families. Besides, KITLG is so far the only gene prevailingly involved in unilateral isolated hearing loss. We therefore conducted a retrospective study of patients with KITLG alterations in the French national Reference Network for Genetic Hearing Loss and one case was added through the Genematcher exchange platform. We describe a series of monoallelic KITLG deletions and variations in a cohort of 14 symptomatic patients from eight unrelated families. All patients presented with unilateral, bilateral symmetric or asymmetric sensorineural hearing loss. When not profound, hearing loss was predominant on low frequencies. Most KITLG alterations are likely to result in loss-of-function and aggregate in the extracellular region, disrupting the KIT-binding domain or its structure. Penetrance is not complete, and unspecific pigmentation alterations were observed in only three patients. The present study confirms KITLG involvement in isolated unilateral, bilateral symmetric or asymmetric hearing loss. This confirmation indicates that genetic testing can be relevant in early-onset, non-sudden, isolated unilateral hearing loss.