Down Syndrome (cont.)

Medical Author:

Sietske N. Heyn, PhD

Sietske N. Heyn, PhD

Sietske N. Heyn is a medical writer with a PhD in neuroscience. Dr. Heyn's education includes a BS with honors from the University of Oregon, and a doctoral degree in neuroscience from the University of California at Davis. After completing postdoctoral training at the University of California, San Francisco, and many years of working as a medical writer at the Stanford University Center for Down Syndrome Research, Dr. Heyn now runs her own medical writing business.

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Medical Editor:

David Perlstein, MD, MBA, FAAP

David Perlstein, MD, MBA, FAAP

Dr. Perlstein received his Medical Degree from the University of Cincinnati and then completed his internship and residency in pediatrics at The New York Hospital, Cornell medical Center in New York City. After serving an additional year as Chief Pediatric Resident, he worked as a private practitioner and then was appointed Director of Ambulatory Pediatrics at St. Barnabas Hospital in the Bronx.

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Although the severity of Down syndrome ranges from mild to severe, most individuals with Down syndrome have widely recognizable physical characteristics. These include:

• a flattened face and nose, a short neck, a small mouth sometimes with a large, protruding tongue, small ears, upward slanting eyes that may have small skin folds at the inner corner (epicanthal fold);
  
  
• white spots (also known as Brushfield spots) may be present on the colored part of the eye (iris);
  
  
• the hands are short and broad with short fingers, and with a single crease in the palm;
  
  
• poor muscle tone and loose ligaments are also common; and
  
  
• development and growth is usually delayed and often average height and developmental milestones are not reached.

Several noninvasive screening options are offered to parents. If Down syndrome is suspected due to the screening outcome, a formal diagnosis can be made before the baby arrives. This gives parents time to gather information about Down syndrome before their baby is born and to make arrangements in case of medical complications.

Prenatal screening tests currently available include the expanded alpha-fetoprotein (AFP) screening test, the nuchal translucency test, and additional ultrasound screens which look for changes in certain anatomical features of the fetus. While these screening tests can assess the risk for Down syndrome, they cannot confirm Down syndrome with certainty.

The most widely used screening test is the AFP. Between weeks 15 and 20 of pregnancy, a small blood sample is taken from the mother and examined. The levels of AFP and three hormones called unconjugated estriol, human chorionic gonadotropin, and inhibin-A are measured in the blood sample. If the AFP and hormone levels are altered, Down syndrome can be suspected, but not confirmed. Likewise, a normal test result does not rule out Down syndrome.

The nuchal translucency test measures the thickness of the fold in the neck via ultrasound. This test can be done between 11 and 13 weeks of pregnancy. In combination with the mother's age, this test identifies about 80% of Down syndrome fetuses.

Women considered at high risk (advanced maternal age, positive AFP test, or a history of a previous child with Down syndrome) may benefit from additional ultrasound scans between 18 and 22 weeks of pregnancy. When certain anatomical features are altered, absent, or present in a fetus, it may indicate Down syndrome. Some of the markers that are examined include:

• the length of the long arm (humerus) or leg bone (femur),
  
  
• the length of the nasal bridge,
  
  
• the size of the renal pelvis (hypoplasia, pyelectasis),
  
  
• small bright spots in the heart (echogenic intracardiac foci),
  
  
• small middle section of the little finger (hypoplastic fifth digit),
  
  
• a large gap between the first and second toe,
  
  
• increased brightness of the bowel (echogenic bowel), and
  
  
• pelvic bone angle (widened iliac angle).

Source: MedicineNet.com
http://www.medicinenet.com/down_syndrome/article.htm