Nance–Horan syndrome in females due to a balanced X;1 translocation that disrupts the NHS gene: Familial case report and review of the literature

Laura Gómez-Laguna, Alejandro Martínez-Herrera, Alejandra del Pilar Reyes-de la Rosa, Constanza García-Delgado, Karem Nieto-Martínez, Fernando Fernández-Ramírez, Tania Yanet Valderrama-Atayupanqui, Ariadna Berenice Morales-Jiménez, Judith Villa-Morales, Susana Kofman, Alicia Cervantes, Verónica Fabiola Morán-Barroso

The Nance-Horan syndrome is an X-linked disorder characterized by congenital cataract, facial features, microcornea, microphthalmia, and dental anomalies; most of the cases are due to NHS gene mutations on Xp22.13. Heterozygous carrier females generally present less severe features, and up to 30% of the affected males have intellectual disability. We describe two patients, mother and daughter, manifesting Nance-Horan syndrome. The cytogenetic and molecular analyses demonstrated a 46,X,t(X;1)(p22.13;q22) karyotype in each of them. No copy-number genomic imbalances were detected by high-density microarray analysis. The mother had a preferential inactivation of the normal X chromosome; expression analysis did not detect any mRNA isoform of NHS. This is the first report of Nance-Horan syndrome due to a skewed X chromosome inactivation resulting from a balanced translocation t(X;1) that disrupts the NHS gene expression, with important implications for clinical presentation and genetic counseling.