Although SMS is caused by a deletion of genetic material, it usually does not run in families. In most cases, the deletion occurs accidentally in a child around the time he or she is conceived, without being inherited from either parent. For this reason, we can say that SMS is clearly genetic, but not usually familial. The risk to siblings depends on the results of parental chromosome analysis. If parental chromosomes are normal, the risks to subsequent pregnancies are extremely low. Families are advised to consult a genetics counselor or specialist for further advice regarding their own particular family situation.
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