Aniridia

If the homeotic gene PAX 6 is mutated the result is a child born with complete loss of the iris. This condition is known as aniridia and like Waardenburg's syndrome it is very rare. If there is no iris in the eye it is impossible to control the inlet of light - the iris is an analogue to the aperture of the camera. The pupil stands wide open, no matter how light it is. The only treatment of aniridia is as yet the use of coloured eye lenses in order to reduce the light inlet.

Experimental studies in mice have shown that disturbances in homeotic genes can cause a malformation of the colon called megacolon. This condition implies heavy enlargement of a certain part of the colon. In small children doctors sometimes diagnose cases of megacolon with unknown origin. It is to be hoped that researchers in the future may be able to find out if malformations of this kind are due to defective genes. This also applies to certain cases of cleft palate, lips and jaw.