Patau's Syndrome

Trisomy 13. It is also known as the Bartholin Patau syndrome

It is a rare congenital disorder caused by an extra number 13 chromosome instead of the usual pair. Mosaics can occur in which some cells are normal with 46 chromosomes and others have the extra one. The mosaic variations tend to be less severely affected. In some variations there are only 46 chromosomes but two chromosomes are fused or joined end on end into one. Hence, whilst there are only 46 chromosomes to be counted, the extra genetic material is there. This is called translocation.

The incidence is given as 1 in 6,000 births but may be falling due to antenatal screening and selective termination of pregnancy. A very large study from Denmark gave an incidence of just in excess of 1 in 30,000 between 1977 and 1986.¹ The sex ratio is equal.² This is the least common and the most severe of the viable trisomies.

A personal or close family history of giving birth to an affected child increases the risk. Risk rises with rising maternal age³ but not as markedly as with Down's syndrome (trisomy 21) or Edwards' syndrome (trisomy 18).

Features include:

• Low birth weight
• Abnormalities of the face and head including a small head, abnormalities in the facial and skull bones, sloping forehead and microcephaly.
• Defects in development of the eyes or failure of the eyes to develop at all.
• Deafness.
• Cleft lip and palate.
• Anatomical defects of the brain and skull.
• Scalp defects called cutis aplasia.
• Severe learning disability.
• Problems with control of breathing.
• Abnormalities of hands and feet including polydactyly (extra fingers or toes).
• Heart defects occur in more than 90% and include atrial septal defect, ventricular septal defect, patent ductus arteriosus and transposition of the great vessels.
• Genital abnormalities including micropenis or hypertrophy of the clitoris.

Patau's syndrome and Edwards' syndrome can look very similar.

Chromosome analysis will confirm the diagnosis. Parents should also have chromosome analysis in case of balanced translocation although the risk to subsequent pregnancies seems small. Balanced translocation is when there is fusion of two chromosomes,or joining end on end but if the total number of chromosomes is counted it appears to be 45 and the total amount of genetic material is normal.

A study from Leicester³ looked at 44 cases of Patau's Syndrome and 88 cases of Edwards' Syndrome (trisomy 18) and found that 64% of cases were diagnosed because chromosome screening was done after concerns raised by fetal anomaly scanning in the 2nd trimester. In only 3% of cases concern was raised from the abnormalities of the blood screening for Down's Syndrome. In 11% of cases the diagnosis was not made until birth. Hence anomaly scanning is the best method of screening. In a study from Northwick Park, 33% of Down's syndrome, 68% of Edwards' syndrome and 52% of Patau's syndrome were diagnosed before 28 weeks without the use of serum screening. ⁴

Ultrasound examination in the second trimester can show anomalies that are characteristic of trisomy 13 to indicate if fetal karyotyping is advisable. Incorporation of careful assessment of the fetal cardiovascular system increases the detection rate of trisomy 13.⁵

This is a catastrophic experience for the parents who will need a great deal of support and counselling including a risk assessment for future pregnancy. It may help to put them in touch with others who can give support and information. Soft.UK (Support Organisation for Trisomy) gives such support to families affected by all the trisomy syndromes. Its website is listed at the end.

Screening should be offered for future pregnancies. For full trisomy, the risk of recurrence in a future pregnancy is less than 1%.⁶

Treatment of the child is supportive but life sustaining measures are not recommended. Considerable thought and discussion is recommended before undertaking measures such as surgical correction of abnormalities.

Life expectancy is very limited. Most die in the first week and few survive beyond a year. The median age of death is 2.5 days.¹ More than 80% die within a month. Only 5% last 6 months. Many cases never make it to term and are stillborn or spontaneously abort. Feeding difficulties, epilepsy and spinal problems occur in those who do survive. They will be very retarded and suffer enormous problems.

Klaus Patau was a German-born American human geneticist. Patau et al described the syndrome in 1960,⁷ the same year that Edwards et al⁸ described trisomy 18. In that same year, Patau was the second name on a paper by Smith et al⁹ that also described trisomy 18. The clinical appearance of trisomy 13 was first described by Erasmus Bartholin but he was unaware of the aetiology as this was in 1657.