Co-segregation of Norrie disease and idiopathic pulmonary hypertension in a family with a microdeletion of the NDP region at Xp11.3-p11.4.

INTRODUCTION: Norrie disease is a rare X-linked congenital retinal vasculopathy that may be accompanied by sensorineural deafness, mental retardation, and other neurological deficits. Here we present a family in which Norrie disease co-segregated with either early-onset idiopathic pulmonary hypertension or sudden death preceded by a period of progressive dyspnea. Neither Norrie disease, nor its atypical variants described to date, have been associated with this extended clinical phenotype.

METHODS AND RESULTS: Molecular analysis of the Norrie disease gene (NDP) and adjacent loci was performed by multiplex ligation-dependent probe amplification and comparative genomic hybridisation. Affected males in this family showed an inherited hemizygous deletion restricted to NDP and two immediately telomeric genes, monoamine oxidase-B (MAO-B) and monoamine oxidase-A (MAO-A), which encode closely related enzymes that metabolize biogenic amines including serotonin, dopamine, and norepinephrine. Sequencing of the deletion junction showed an unusual pattern in which a region of microhomology flanked intervening genomic sequence.

CONCLUSION: Because abnormalities of biogenic amines, particularly serotonin, have been implicated in the pathophysiology of pulmonary hypertension, we propose that presumed MAO deficiency in these patients may represent a novel risk factor for pulmonary hypertension, particularly forms with very early onset. Fine-mapping of other microdeletions at this locus may provide insights into additional mechanisms for nonrecurrent genomic rearrangements at this and other chromosomal loci.