Carrier Detection

CARRIER DETECTION OVERVIEW

HOW CAN WE DETECT A CARRIER OF LOWE SYNDROME?

Lowe Syndrome is an X-linked genetic defect, which means there is a defect on the X chromosome. In males, there is one X chromosome and one Y chromosome. Should the single X chromosome have the Lowe Syndrome defect, the male child will in fact have Lowe Syndrome. Female carriers of Lowe Syndrome have no outwardly visible symptoms, since females have two X chromosomes, and the additional X chromosome compensates for the chromosome with the defect.

Note that while an enzyme test is available for diagnosis of an affected male child, this test cannot be reliably used to determine Lowe Syndrome carrier status. However, we do have the following techniques available to help determine whether a person is a carrier of Lowe Syndrome.

OPHTHALMOLOGIC EXAMINATION

Observation and research has shown that most female carriers will begin to show lenticular opacities in the eyes at around the age of puberty. These opacities are visible under slit lamp examination. The presense of these specific opacities, especially where there is a strong family history of Lowe Syndrome, can be used to determine whether a person is a Lowe Syndrome carrier. In some cases, some female carriers also have a dense central posterior lens opacity apparent early in life. This opacity if present, has not been shown to diminish or go away over time.

DNA ANALYSIS

DNA analysis, usually in conjunction with a detailed examination of a family’s history can also be used to determine Lowe Syndrome carrier status. The accuracy of this type of testing is considered higher than that of the ophthalmologic examination alone — approximately a 95% accuracy.

CARRIER DETECTION FLOWCHART

The following flowchart depicts the usual steps taken to determine whether someone is a Lowe Syndrome carrier. Without a doubt, the ophthalmologic examination is the easiest to perform, although it cannot be used until a person nears the age of puberty.

OPTHALMOLOGIC EXAMINATION

Female carriers of Lowe Syndrome are known to have a series of “lenticular opacities” arranged in clustered wedge-like patterns in the eye. These opacities can only be viewed under slit lamp examination. Before the advent of DNA analysis and the enzyme deficiency testing, this eye examination was the only thing available.

Observation and research has shown that most female carriers will begin to show lenticular opacities in the eyes at around the age of puberty. These opacities are visible under slit lamp examination. The presence of these specific opacities, especially where there is a strong family history of Lowe Syndrome, can be used to determine whether a person is a Lowe Syndrome carrier. In some cases, some female carriers also have a dense central posterior lens opacity apparent early in life. This opacity if present, will not diminish or go away over time.

The LSA strongly advises that eye examinations for the purpose of determining genetic carrier status be performed only by trained and experienced ophthalmologists who are familiar with the occasionally subtle and very variable features in the lens of the eye. We suggest your ophthalmologist review the images below before performing the slit lamp examination. Each thumbnail image can be enlarged to a high resolution printable image.

These slides have been graciously provided by Dr. Richard A. Lewis, M.D. of the Baylor College of Medicine. For more information, please contact Dr. Lewis at the following address.

RICHARD A. LEWIS, M.D.

Cullen Eye Institute NC-206
Baylor College of Medicine
1 Baylor Plaza
Houston, TX 77030

The following thumbnails and full-size images are copyrighted by the Baylor College of Medicine.

Carrier Slide 1
Carrier Slide 2
Carrier Slide 3
Carrier Slide 4
Carrier Slide 5
Carrier Slide 6