I understand that at one of the UK examination centres, a case of Nail Patella syndrome was included in the skin station.

This had been a difficult case

If one had never seen such a case before it would have been very difficult to make a diagnosis.

Reading about it may have helped but it would be doubtful

This is where first principles comes in

Remember that examination is looking at structure and function of the body and looking for any deviation from normal (ACES for PACES chapter 5 page 27)

When examining the nails the first step, as in any examination, is to look at the dimensions (ACES for PACES chapter 5 page 29)

If one followed this one would have noticed that the nails were small.

Small, deformed nails occur in the nail patella syndrome  (ACES for PACES pages 126,332)

If one had been asked to examine the knees then one would have noticed absence of the patella and this would have confirmed the diagnosis of nail patella syndrome