“…Uncertainty persists regarding exact diagnostic criteria. For example, some studies, such as the relatively large clinical series described by Weaver et al in 1986 [39], required the presence of two component features for diagnosis, while others, including a follow-up study on that series [40], require at least three component features [3, 4, 14, 29]. While several genetic causes have been implicated in a small number of human patients or in animal models [6, 11, 16, 27, 30, 34, 36], evidence of causality has not been uniform, and no consistent etiology has been identified.…”