Human Molecular Genetics, Vol 4, 1729-1737, Copyright © 1995 by Oxford University Press
ZY Chen, RM Denney and XO Breakefield
The Norrie disease and MAO genes are tandemly arranged in the p11.4- p11.3
region of the human X chromosome in the order tel-MAOA-MAOB-NDP- cent. This
relationship is conserved in the mouse in the order tel-MAOB-
MAOA-NDP-cent. The MAO genes appear to have arisen by tandem duplication of
an ancestral MAO gene, but their positional relationship to NDP appears to
be random. Distinctive X-linked syndromes have been described for mutations
in the MAOA and NDP genes, and in addition, individuals have been
identified with contiguous gene syndromes due to chromosomal deletions
which encompass two or three of these genes. Loss of function of the NDP
gene causes a syndrome of congenital blindness and progressive hearing
loss, sometimes accompanied by signs of CNS dysfunction, including variable
mental retardation and psychiatric symptoms. Other mutations in the NDP
gene have been found to underlie another X-linked eye disease, exudative
vitreo-retinopathy. An MAOA deficiency state has been described in one
family to date, with features of altered amine and amine metabolite levels,
low normal intelligence, apparent difficulty in impulse control and
cardiovascular difficulty in affected males. A contiguous gene syndrome in
which all three genes are lacking, as well as other as yet unidentified
flanking genes, results in severe mental retardation, small stature,
seizures and congenital blindness, as well as altered amine and amine
metabolites. Issues that remain to be resolved are the function of the NDP
gene product, the frequency and phenotype of the MAOA deficiency state, and
the possible occurrence and phenotype of an MAOB deficiency state.
REVIEWS
Norrie disease and MAO genes: nearest neighbors
Department of Neurology, Massachusetts General Hospital, Boston 02114, USA.
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