Schaaf-Yang Syndrome: An Example of Genomic Imprinting and Expanding Phenotype

Abstract

Schaf-Yang Syndrome is a rare genetic condition, produced by a mutation in the MAGEL2 gene, located at the level of chromosome 15, in the Prader-Willi Syndrome region, with which it shares some physical similarity. The phenotype is variable and ranges from fetal akinesia to an important neurobehavioral phenotype and contractures of the small finger joints that are very characteristic. The gene has a maternal imprint and the phenotype will only be expressed when the mutated allele has been transmitted parentally. We present the case of a 2-and-a-half-year-old male from Ecuador, whose most prominent signs were in the beginning a marked macroglossia that gave a certain rough facial appearance, as well as bilateral camptodactyly of the 3rd and 4th fingers. The history of a previous sister who died at age 8 with a diagnosis of hypothyroidism, and clinical similarity to this new baby, led the clinical orientation to the screening of a potentially autosomal recessive condition. The genetic tests performed as part of the differential diagnosis where to pathologies such as Becwith-Wiedeman Syndrome, Mucopolysaccharidosis and Congenital Hypothyroidism. The clinical elements of this case are compared with those described in the literature with this rare genetic syndrome, and the clinical evolution of dysmorphic patterns in young children is emphasized in order to achieve a better diagnostic certainty. We emphasize the features of macroglossia as a probably expanding phenotype in this rare condition. The presentation of this clinical case shows that the factors that alter the segregation of simple mutations such as the case of the genetic imprint, found in this patient, constitute an event that hinders the interpretation of inheritance patterns and should always be taken into account in genetic counseling.