What is Nance-Horan Syndrome (NHS)?
Nance Horan syndrome is a rare cause of cataracts in children – most children with cataracts do not have Nance Horan syndrome but there are thought to be a few children with cataracts who have this condition who are only mildly affected by it, and therefore have not had a diagnosis. This is a brief overview of Nance Horan syndrome written by Miss Isabelle Russell-Eggitt in response to a number of parents on the CCN email group who had noticed that their child with cataracts had unusual problems with their teeth:
“Nance-Horan Syndrome is a genetic disorder inherited through the female line in a family. A father cannot pass this type of cataract on to his son. This disorder is only passed on by a mother to her sons and daughters with a 50% chance that each will have the condition themselves.
Congenital cataract is a main feature, but expression of the gene varies widely between individuals with many girls and mothers having no obvious eye problem and most boys having dense cataracts and slightly small eyes. Some boys may be more mildly affected having only a minimal cataract in one eye and some girls may have a dense cataract in one eye.
This disorder is often not diagnosed and a label of ‘congenital cataract’ or ‘inherited cataract’ is given. This is due to a combination of lack of awareness of this disorder even amongst paediatric ophthalmologists and that many children have a milder condition than the classic textbook case. It is helpful for the family and specialists to have the correct diagnosis so that the other features do not go undetected and the child receives the best possible care.
The eye of an affected individual not only has a cataract but often in a male is slightly small making them a less likely candidate for an intraocular lens early in life. Surgery may be more difficult with a higher risk of bleeding inside the eye during the procedure and a higher risk of glaucoma. The optic disc may look slightly unusual and in some cases the ‘cup’ in the disc may be thought to be due to glaucoma when the eye pressure is normal and this is just the way the disc developed. Many individuals with NHS do achieve good vision yet some in spite of the best possible care do have complications and a poor outcome.
Nance-Horan also affects the development of teeth. As with the eyes the teeth may be totally normal in some family members who have the NHS gene and in others the teeth have an abnormal shape and poor enamel and are therefore very prone to caries.
Many individuals with the NHS gene thrive at school, but some do have behavioural or learning difficulties that in a few cases may be severe.
The name of the disorder comes from the names of 2 doctors, Nance and Horan who independently first described cases in the medical literature. The gene which is defective is now known but testing for defects in this gene is not yet available at one of the UK reference laboratories. Occasionally a gene test may be offered by one of the centres doing research into the ‘cataract genes’, but pre-natal diagnosis is not at present available. The diagnosis is usually made on features especially on the milder cataract type seen in some girls in the family and on the teeth shape. The shape of the external ears may also be suggestive of NHS, being often slightly cup shaped and prominent.”
If you feel that your child with cataracts may be affected by Nance Horan syndrome, your child’s ophthalmologist or GP should be able to refer your child to a paediatrician.
Checked for medical accuracy by Miss Isabelle Russell-Eggitt, Consultant Paediatric Ophthalmologist, Great Ormond Street Hospital, London