What is Nance-Horan syndrome?
Nance-Horan syndrome is a rare, genetic, congenital disorder that is characterized by teeth abnormalities and vision loss caused by congenital cataracts. Some also have intellectual disabilities.
While the exact incidence of this disorder is unknown, fewer than 50 families have been reported to have this condition. It is suspected that many people with Nance-Horan syndrome go undiagnosed or are misdiagnosed, which makes it very difficult to know exactly how many people have this syndrome. It is more prevalent in males than females, as it is an X linked disorder, but females may still present some of the symptoms even without having two copies of the mutated gene.
What are the symptoms of Nance-Horan syndrome?
The main symptom of this syndrome is congenital cataracts in both eyes. These cataracts can cause blurry vision and a severe loss of clarity. Other abnormalities of the eyes may also occur, including a small cornea, misalignment of the eyes, a drooping of the upper eyelid, and involuntary eye movements.
Dental abnormalities are the other main symptoms of Nance-Horan syndrome. Teeth may be unusually shaped, absent, impacted, or have wide spaces between them. Front teeth are shaped like screwdrivers and tapered, while posterior teeth may be conical and rounded. Some people with this disorder have an extra tooth in the center of the upper jaw. Baby and adult teeth are affected by this condition.
Subtle but distinctive facial features may also affect people with this syndrome. Flared and prominent ears with folded lobes, a prominent nose with a high nasal bridge, and a prominent jaw are all characteristics of this disorder.
Less common symptoms include delays of physical and mental developments and intellectual disabilities. These intellectual disabilities are typically mild, but in certain cases they may be severe. It is believed that 20-30% of people with Nance-Horan syndrome have an intellectual disability.
While this disorder is more common in males, it may also partially present itself in females who only carry one copy of the mutated gene. Heterozygous females tend to only experience milder forms of the ocular and dental symptoms.
What causes Nance-Horan syndrome?
Nance-Horan syndrome is caused by a mutation of the NHS gene, which is on the X chromosome. The function of this gene is not fully understood. Males are more likely to have this disorder than females; they only have to inherit one mutated gene in order for it to be present, as they only have one X chromosome. Females with only one copy of the mutated NHS gene may also present some symptoms, but they will be milder.
How is Nance-Horan syndrome diagnosed?
A clinical evaluation is the first step in diagnosing this disorder, followed by specialized testing, such as examining the interior of the eyes and dental x-rays. Genetic testing can confirm the diagnosis. It can also tell if females carry the disorder.
What are the treatments for Nance-Horan syndrome?
Treatment for Nance-Horan syndrome is symptomatic. Surgery can be conducted to remove cataracts or to implant artificial lenses. Vision can also be improved through corrective lenses, contact lenses, or other measures.
In terms of dental symptoms, surgery can be conducted to remove the additional tooth or correct other abnormalities. Braces or other dental procedures may correct the wide spaces between teeth.
Females that carry the gene for this disorder should monitor their vision to ensure that they are not symptomatic.