The MASA syndrome: A new heritable mental retardation syndrome

Two Mexican-American children of West Texas are described: a brother and sister with a similar pattern of malformation. They have in common a tetrad of Mental retardation, Aphasia, Shuffling gait, and Adducted thumbs. Besides these two sibs, who were available for study, it is known that a total of seven members of this kindred, six males and one female, spanning three generations, have been similarly affected. Although all members of this family come from the same ethnic background, consanguinity has been denied. The mode of inheritance cannot be firmly established at this time. It is in our opinion most compatible with that of an X-linked recessive gene with phenotypic expression in only one female due to unfavorable Lyonization. Other possibilities exist which cannot be entirely excluded. These include an autosomal dominant mutation with incomplete penetrance in at least three obligatory carrier females. Another possible mechanism is that of an autosomal recessive gene, since all members of this pedigree are of the same Mexican ancestry (Fig. 1. II-1, III-3, III-6). Because all affected members exhibit the four cardinal features of this disorder: Mental retardation, Aphasia, Shuffling gait, and Adducted thumbs, wc wish to refer to this heritable condition as the MASA syndrome until the basic defect is further characterized.