Prenatal diagnosis of inherited skin conditions

What is prenatal diagnosis?

Prenatal diagnosis is the identification of a medical condition before an infant is born. This may be undertaken during pregnancy, or prior to implantation of an embryo during in-vitro fertilisation.

What is the difference between prenatal screening and prenatal diagnosis?

Prenatal screening is a means of assessing if a fetus is at increased risk of an abnormality. Screening is routinely offered to all pregnant women in developed countries, and is performed during the first and second trimester (up to 26 weeks of gestation). Screening involves a fetal ultrasound and maternal blood tests. Abnormalities screened for are those considered to have significant morbidity/mortality.

Prenatal diagnosis is the determination of a specific medical condition using genetic testing, immunohistochemistry and electron microscopy. As with prenatal screening, prenatal diagnosis is only indicated for conditions associated with significant morbidity/mortality.

Why is prenatal diagnosis undertaken?

Prenatal diagnosis is performed for the following reasons:

• Provides expectant parents with the choice to continue or have a termination of pregnancy in the setting of a known diagnosis of a severe inherited skin condition.
• Allows for optimal preparation for the birth and initial care of the neonate;
  • Parents can be appropriately counselled and prepare themselves.
  • Potential complications of the delivery can be anticipated, such as increased risk of failure to progress during labour in the setting of a fetus with X-linked ichthyosis.
  • Delivery can be arranged to take place in a suitable facility with access to a Neonatal Intensive Care Unit.

What skin conditions can be diagnosed prenatally?

Skin conditions suitable for prenatal diagnosis include:

• Epidermyolysis bullosa
• Ichthyotic disorders
• Oculocutaneous albinism
• Ectodermal dysplasia syndromes

The causative gene mutation of many other inherited skin conditions are known; however, prenatal testing should only be performed for disorders with high morbidity/mortality.

Is determination of fetal sex important in prenatal diagnosis of skin conditions?

The sex of the fetus can be very important in prenatal diagnosis of inherited skin conditions. Incontinentia pigmenti is an X-linked dominant condition that is usually fatal in male fetuses, and affects females to varying degrees. X-linked ichthyosis results in skin disease in males; female carriers are unaffected or may develop asymptomatic corneal opacities.

Methods and timing of prenatal diagnosis

The tests used for prenatal diagnosis are described in the table below.

What are the potential complications of prenatal diagnosis?

The potential complications of prenatal diagnosis are specific to the technique used:

Pre-implantation genetic diagnosis

• Risk of misdiagnosis: technically difficult and small cell number available to use for genetic analysis
• Lower pregnancy rates compared to IVF without prenatal diagnosis
• Very costly

CVS, amniocentesis and fetal skin biopsy

• Small risk of fetal loss (1–3%)
• Amniotic fluid leakage
• Rhesus blood group sensitisation in a Rhesus-negative mother

Fetal skin biopsy

• Scarring (usually minor) of newborn
• Inconclusive results if performed too early (prior to adequate fetal skin formation)

Can treatment of the skin condition be given prior to birth?

There is currently no means of treating inherited skin conditions prior to delivery of the infant. Further advances in fetal medicine may make this a possibility in the future.