Hallermann-Streiff syndrome: A missing molecular link for a highly recognizable syndrome.

The use of modern next-generation sequencing-based approaches for gene identification has tremendously improved our understanding of the molecular pathogenesis of the great majority of well-known syndromes, whereas only a few remain to be elucidated. Hallermann-Streiff syndrome is such a disorder for which the molecular basis is still unknown although it represents a highly recognizable phenotype. Clinically, patients with Hallermann-Streiff syndrome show typical craniofacial dysmorphism, eye malformations, a distinctive facial appearance, abnormalities of hair and skin, short stature, and, interestingly, they might also present with aspects of premature aging. The clinical diagnosis is mainly given by the very typical facial gestalt of patients. In this review, we (a) summarize the current knowledge on the phenotypic traits, focusing on described classic cases, (b) discuss the missing molecular link, and (c) present innovative future strategies for gene identification.