It is possible that the main title of the report Marfan Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.
As Jenny points out, being able to lisp the alphabet song at age two has little to do with 'knowing' the alphabet. And, yes, most children learn the letters by sight and sound in kindergarten, although most are capable of learning this information sooner if diligently taught by parents or others.
There are TONS of kids that do not even know their letters and numbers when they go into kindergarten! I have a degree in early childhood and most children learn these things when they are 3-4 years old. Of course, the more you work with them, the faster they will learn. My daughter is 32 months. She has known all of her colors, body parts, animal sounds and shapes by 18 months.