A few days ago, this image surfaced on Reddit, showing a young lady suffering from Cat-Eye Syndrome – or as it is scientifically called, Schmid–Fraccaro syndrome. Since then the image has popped up on several mediums of the internet, with many misconceptions and downright false claims popping up as well – so let’s take a look at what the science says about this one.

Cat-Eye Syndrome (CES) is a very serious and rare genetic condition characterized by modifications of chromosome 22 (partial trisomy or tetrasomy). This means that the top half of the 22nd chromosome (the “p” arm) and a small section of the bottom half (“q” arm) are present three or four times in the cells of the body, rather than 2 times, as is normal. The problem has been identified for more than a century, but cat eye syndrome was more specifically defined in 1965, when researchers reported that some affected individuals have only one or neither of these features.

The term “cat-eye” is used because a distinctive eye (ocular) abnormality occurs in some of the affected individuals; this feature consists of partial absence of ocular tissue (coloboma), often affecting both eyes (bilateral), leading to the blackened area which looks like a cat eye. However, not all people suffering from this syndrome exhibit this abnormality – about half of them have regular looking eyes.

Unfortunately, as cool as this might look, there is a number of issues associated with this condition. Although there is no significant reduction in life expectancy in patients who are not afflicted with one of CES’ life-threatening abnormalities, many people with CES suffer from:

  • several ocular defects, including downslanting eyelid folds (palpebral fissures), widely spaced eyes (ocular hypertelorism)
  • small depressions or growths on the ears (preauricular pits/tags)
  • kidney problems (missing, extra, or underdeveloped kidneys)
  • short stature
  • hernia
  • intellectual disability – only a fraction of CES sufferers have normal intelligence
  • cardiac defects (such as TAPVR)
  • skeletal defects
  • a number of other organ-related issues.

These associated symptoms vary greatly in occurrence and intensity – while some people have very few or no significant manifestations, others can exhibit the full spectrum of manifestations.

It’s not clear how many people suffer from CES, but studies conducted in Switzerland concluded that it may affect 1 in 50,000 to 1 in 150,000 people. Because some affected individuals develop few associated features, this may be an underestimate.

Disease management can be quite difficult, required a special tailored approach for each case. Chromosomal studies may be recommended for parents of affected individuals, such as to determine whether they exhibit mosaicism for the marker chromosome. Research is currently underway to determine whether there is a connection between the size of a person’s cat eye syndrome chromosome and the number and severity of symptoms the person shows.