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.
Many children (who have had no experience with school) don't know their colors until they attend kindergarten. Counting rote to ten can come between 2 and 4 also, with most children (if they don't have a speech problem) being able to do this at 3. Singing the ABCs is accomplished at age 3...