Causes
A number of factors can cause a fetus to develope an irregular Chormosome count. The normal child has exactly 46 chromosomes. An abonormal child has more or less chromosomes.

Here is a chromosome set of an abnormal human. Notice that this person has an expra X chromosme. Usually, the more sex chromosomes misplaced in a gene sequence, the more server the retardation. Down Syndrome is such a case. Some victims have as many as 5 misplaced chromosomes. Many criminals have extra chromosomes.

Substance abuse: (from http://www.accessone.com/~delindam/fas-assess.html )

Subtance abuse may also cause bird defects. FAE stands for Fetal Alcohol Effects and FAS stand for Fetal Alcohol Syndtrome.

• Are often exhausted and irritable
• Are a danger to self and others because they act before they think.
• Are short and skinny.
• May be delayed in toilet training sometimes to age 6.
• Enter puberty at age-appropriate times, but their reasoning and judgment skills are a tragically impaired guide to appropriate times and places to express sexual curiosity.
• Need constant reminders about personal hygiene issues much like during the toddler years.
• Are unable to comprehend how their behavior relates to consequences.
• Are unaware of the universal laws of nature, such as cause and effect.
• Are very mischievous and do not understand that their thoughtless pranks.
• Are emotionally volatile and often exhibit wide mood swings throughout the day.
• Depression can become a serious problem as social opportunities become more and more rare.