Also called crib death, sudden infant death syndrome is a medical mystery of early infancy. It kills apparently healthy infants, usually between ages 4 weeks and 7 months, for reasons that remain unexplained, even after an autopsy. Typically, parents put the infant to bed and later find him or her dead, often with no indications of a struggle or distress of any kind. Some infants may have had signs of a cold, but such symptoms are usually absent. Sudden infant death syndrome has occurred throughout history, allover the world, and in all climates.

What causes it?

Sudden infant death syndrome accounts for 7,500 to 8,000 deaths annually in the United States, making it one of the leading causes of infant death. Most of these deaths occur during the winter, in poor families, and among underweight babies and those born to mothers under age 20.

Although infants who die from this disorder often appear healthy, research suggests that many may have had undetected abnormalities, such as an immature respiratory system and respiratory dysfunction. In fact, the current thinking is that it may be caused by an abnormality in the control of breathing, which causes apnea (prolonged non­breathing periods) with profound hypoxemia (decreased oxygen in the blood) and irregular heartbeats. Bottle feeding, instead of breast­feeding, and advanced parental age don't cause sudden infant death syndrome.

Although parents find some victims wedged in crib corners or with blankets wrapped around their heads, autopsies rule out suffocation as the cause of death. Even when blood-tinged sputum is found around the infant's mouth or on the crib sheets, autopsy shows an open airway, so choking on vomit is not the cause of death. Typically, these infants don't cry out and show no signs of having been disturbed in their sleep, although their positions or tangled blankets may suggest movement just before death, perhaps due to terminal spasm.

What are its symptoms?

Depending on how long the infant has been dead, the infant may have a mottled complexion with extreme bluish discoloration of the lips and fingertips, or pooling of blood in the legs and feet that looks like bruises. Pulse and respirations are absent, and the infant's diaper is wet and full of stools.

How is it diagnosed?

Diagnosis of sudden infant death syndrome requires an autopsy to rule out other causes of death. Characteristic histologic Endings on autopsy include small or normal adrenal glands and petechiae over the visceral surfaces of the pleura, within the thymus (which is enlarged), and in the epicardium. Autopsy also reveals extremely well­preserved lymph structures and certain disease characteristics that suggest chronic hypoxemia, such as increased pulmonary artery smooth muscle. Examination also shows swollen, congestive lungs fully expanded in the pleural cavities, liquid (not clotted) blood in the heart, and curd from the stomach inside the windpipe.

How is it treated?

If the parents bring the infant to the emergency room, the doctor will decide whether to try to resuscitate him or her. In "aborted sudden infant death syndrome," an infant who is not breathing is successfully resuscitated. Such an infant, or any infant who had a sibling stricken by this disorder, should be tested for infantile apnea. If tests are positive, a home apnea monitor may be recommended.

Because most infants cannot be resuscitated, however, treatment focuses on emotional support for the family.