The Genome

CMECNE

Turner Syndrome – 45,X Explained

Learning Objectives and CME/Disclosure Information

This activity is intended for healthcare providers delivering care to women and their families.

After completing this activity, the participant should be better able to:

1. Describe the findings associated with Turner syndrome and consequent monitoring
2. Explain the recurrence risk to prospective parents

Estimated time to complete activity: 0.25 hours

Faculty:

Susan J. Gross, MD, FRCSC, FACOG, FACMG
President and CEO, The ObG Project

Disclosure of Conflicts of Interest

Postgraduate Institute for Medicine (PIM) requires faculty, planners, and others in control of educational content to disclose all their financial relationships with ineligible companies. All identified conflicts of interest (COI) are thoroughly vetted and mitigated according to PIM policy. PIM is committed to providing its learners with high quality accredited continuing education activities and related materials that promote improvements or quality in healthcare and not a specific proprietary business interest of an ineligible company.

The PIM planners and others have nothing to disclose. The OBG Project planners and others have nothing to disclose.

Faculty: Susan J. Gross, MD, receives consulting fees from Cradle Genomics, and has financial interest in The ObG Project, Inc.

Planners and Managers: The PIM planners and managers, Trace Hutchison, PharmD, Samantha Mattiucci, PharmD, CHCP, Judi Smelker-Mitchek, MBA, MSN, RN, and Jan Schultz, MSN, RN, CHCP have nothing to disclose.

Method of Participation and Request for Credit

Fees for participating and receiving CME credit for this activity are as posted on The ObG Project website. During the period from Dec 31 2017 through Jan 25 2023, participants must read the learning objectives and faculty disclosures and study the educational activity.

If you wish to receive acknowledgment for completing this activity, please complete the test and evaluation. Upon registering and successfully completing the test with a score of 100% and the activity evaluation, your certificate will be made available immediately.

Joint Accreditation Statement

In support of improving patient care, this activity has been planned and implemented by the Postgraduate Institute for Medicine and The ObG Project. Postgraduate Institute for Medicine is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

Physician Continuing Medical Education

Postgraduate Institute for Medicine designates this enduring material for a maximum of 0.25 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Continuing Nursing Education

The maximum number of hours awarded for this Continuing Nursing Education activity is 0.2 contact hours.

Read Disclaimer & Fine Print

WHAT IS IT?

Also known as 45,X ; monosomy X; Turner’s syndrome; Ullrich-Turner syndrome
A sex chromosome abnormality that involves the presence of one functional X chromosome and no other X or Y chromosome
- All cells can be monosomy X (having a single X chromosome) or
- There can be a mix of cell lines, where some cells are normal (46,XX) and others have only one X chromosome (mosaic Turner syndrome)
Common findings on prenatal ultrasound:
- Increased nuchal translucency (1st trimester), nuchal fold (2nd trimester), or cystic hygroma
- Cardiac defects
  - Bicuspid aortic valve and coarctation of the aorta
- Renal defects (i.e. horseshoe kidney)
Other findings may not be apparent until postnatal life
- Short stature is usually the most consistent finding, approximately 8 inches less than what would be expected for her family
  - Genetic mechanism resulting in short stature still unknown, however the absence of the SHOX gene, located on short arm of X chromosome, which helps coordinate bone development, is likely an important factor
- Wide or webbed neck
- Low-set ears
- Low hairline at the back of the head
- Broad chest with widely spaced nipples
- Lymphedema, especially of the hands and feet
- Absent, delayed, or partial spontaneous pubertal development (30%)
- Absent or decreased fertility, depending on what percentage of cells have only one X chromosome, as two X chromosomes are required for ovarian development and function
Intellectual development:
- Females who have a 45,X karyotype usually have normal intelligence although there may be some learning disabilities, particularly with mathematical and spatial concepts, some difficulty in social situations
Treatment and monitoring:
- Cardiology monitoring
- Growth hormone and hormone replacement therapy
- Academic support for potential learning challenges
- Fertility assessment

CAUSE:

Turner syndrome (45,X) is a condition caused by an abnormal karyotype that is present at the time of conception and results from a sperm or egg that is capable of undergoing fertilization, but has no X chromosome. As this appears to be a random event, Turner syndrome is generally not inherited and risk of recurrence in subsequent pregnancies is minimal.

KEY POINTS:

ACOG requires all women be offered prenatal screening (biochemical/ cfDNA) or invasive diagnostic testing (amniocentesis/ CVS)
- Turner (45,X) syndrome is included on some cfDNA screening panels but is associated with a higher false positive rate compared to Down syndrome
- Confirmatory testing (amniocentesis or CVS) should be offered all women with a positive cfDNA screening report
  - Presently, invasive testing is the only way to diagnose fetal Turner syndrome
  - There is data supporting the use of amniocentesis rather than CVS for confirmation
Present in 1/1500- 1/2500 live births
Estimated to account for 3% of all conceptions
Despite relatively functional outcomes, approximately 99% of cases are miscarried or stillborn
- Mosaic Turner syndrome has a better chance of survival
ACMG provides ACT sheets to assist healthcare professionals with ‘next steps’ following a positive NIPS report for 45,X (see ‘Learn More – Primary Sources’ below)

Learn More – Primary Sources:

ACMG: Noninvasive Prenatal Screening via Cell-Free DNA ACT Sheet [45,X: Positive Cell Free DNA Screen]

NHGRI: Turner syndrome

US NLM- Genetics Home Reference

The type of feto-placental aneuploidy detected by cfDNA testing may influence the choice of confirmatory diagnostic procedure

ACOG Practice Bulletin 226: Screening for Fetal Chromosomal Abnormalities

Locate a Genetic Counselor or Genetics services:

Genetic Services Locator-ACMG

Genetic Services Locator-NSGC

Genetic Services Locator-CAGC

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