Familial Thymic Aplasia — Genetic Defect or Maternal Effect

To the Editor: Recently, Steele et al. described in the Journal¹ the first cases of familial aplasia of the thymus and parathyroids. They concluded that in this family the disorder was genetic. The partial deficiencies of thymic and parathyroid function in the mother of the two affected infants were cited as evidence for maternal transmission, either by autosomal dominant or by X-linked dominant inheritance. Although variable penetrance of dominant genes is common, it seems possible that the familial pattern is due to a nongenetic mode of transmission. Indeed, maternal pharmacologic, infectious or metabolic factors may affect fetal development. In this. No extract is available for articles shorter than 400 words.