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.
The babbling will start making sense as your child will begin imitating your language. He or she should also respond to sounds by eye contact and turning his or her head in the direction of sounds. By the end of 18 months, your child will continue to learn new words. However, do not expect too much though. Most children say up to 10 words by the age of 18 months although they understand the meaning of much more words and will point to a familiar object or person when named.