Other Names for this Disease
- Cataract dental syndrome
- Cataract X-linked with Hutchinsonian teeth
- Mesiodens cataract syndrome
What are the signs and symptoms of Nance-Horan syndrome?
What causes Nance-Horan syndrome?
How is Nance-Horan syndrome inherited?
In affected males, the primary physical characteristic is the presence of dense clouding of the lens (cornea) of both eyes at birth (congenital bilateral cataracts). The cataracts usually result in blurred vision and severely decreased clearness or clarity of vision (visual acuity). Vision loss can potentially be profound. Males with Nance-Horan syndrome may have additional eye abnormalities, including a very small cornea (microcornea), involuntary movements of the eyes (nystagmus), and/or misalignment of the eyes (strabismus). In some cases, the entire eye may be abnormally small (microphthalmia) and/or the upper eyelid may droop (ptosis).
Males with Nance-Horan syndrome may also have several dental abnormalities such as unusually shaped, extra (supernumerary) teeth, absence of some teeth (dental agenesis), impacted teeth or unusually wide spaces (diastema) between some of the teeth. The front teeth, or incisors, are usually tapered and 'screwdriver-shaped'. The teeth in the back of the mouth may be cone-shaped, rounded, or cylindrical.
In many males with Nance-Horan syndrome, other physical findings may also occur. Distinctive facial features may be present, but may be subtle. The ears may be flared forward and unusually prominent. Affected males may also have a large, prominent nose with a high, narrow nasal bridge, a narrow prominent jaw, and sometimes a long, narrow face.
Some males with Nance-Horan syndrome may also experience delays the skills necessary for coordinating muscular and mental activity. In addition, some reports suggest that approximately 20 to 30 percent of affected males may have varying levels of intellectual disability, which is usually mild to moderate; but in some cases can be severe.Females who carry a single copy of the mutation in the NHS gene may develop some symptoms of the disorder. However, symptoms are usually milder and more variable than those seen in males. Affected females may have abnormally small corneas (microcornea) and/or some clouding of the cornea. Vision may be normal, or there may be slightly decreased visual acuity. Without appropriate treatment, clouding of the cornea can lead to total cataracts later in life. Females often have some dental abnormalities, such as abnormally-shaped front teeth and/or unusually wide spaces between some of the teeth. Affected females usually do not develop intellectual disability.
X-linked conditions result from mutations of a gene located on an X chromosome. Females have two X chromosomes, but males have one X chromosome and one Y chromosome. In females, disease traits resulting from the abnormal copy of a gene on one X chromosome can be 'masked' by the normal copy of the gene on the other X chromosome. Because only one functioning X chromosome is required in males and females, one of the X chromosomes in each cell of a female is essentially 'turned off,' usually in a random pattern (X chromosome inactivation). Therefore, if the X chromosome with the gene mutation is activated in some cells, female carriers may have some mild features of the disorder. However, since males only have one X chromosome, they will likely fully express a condition if they inherit a gene mutation that is located on the X chromosome.
- Nance-Horan Syndrome. National Organization for Rare Disorders (NORD). 2011; http://www.rarediseases.org/rare-disease-information/rare-diseases/byID/1055/viewAbstract. Accessed 8/22/2011.
- Nance-Horan syndrome. Orphanet. September 2007; http://www.orpha.net/consor/cgi-bin/Disease_Search.php?lng=EN&data_id=931. Accessed 8/22/2011.