It is part of the group of main autosomal trisomies and is due to the presence of an extra copy of chromosome 13 in the body’s cells. Survival, especially in the complete form, is unfortunately very limited. Mortality is high already in the perinatal period and in the first year of life
Patau Syndrome is a rare genetic condition characterized by a complex set of congenital malformations and neurological development involvement.
Understanding what trisomy 13 is, what it depends on and how it is diagnosed can help parents navigate an often unexpected and painful journey.
What is Patau Syndrome
Patau Syndrome is caused by an anomaly of chromosome 13, i.e. the presence of an extra copy in the cells of the organism: normally each cell contains 46 chromosomes, in Patau syndrome chromosome 13 is present in three copies, a condition which profoundly alters embryonic development from the early stages.
The effect of this genetic alteration is particularly relevant because chromosome 13 contains genes involved in the formation of the nervous system, face, heart and other vital organs. For this reason, trisomy 13 is associated with multiple malformations and a very severe clinical picture.
From a historical point of view, the syndrome was described anatomically for the first time in the seventeenth century by Thomas Bartholin (some also report his brother Rasmus), but only in 1960 Klaus Patau, a German geneticist, identified its chromosomal origin and described the associated clinical picture.
Trisomy 13 is part of the group of major autosomal trisomies, together with trisomy 18 (Edwards syndrome) and trisomy 21 (Down syndrome). The differences between trisomy 13 and 18 (therefore between Patau Syndrome and Edwards Syndrome) mainly concern the type of malformations and the possibility of survival, which is decidedly worse for trisomy 13. In the overall comparison between trisomy 13, 18 and 21, Down syndrome presents a significantly better prognosis, while trisomy 13 and trisomy 18 are associated with a more complex situation and with a higher quality of life. unfavorable.
The causes of Patau Syndrome
The causes of Patau Syndrome are mainly linked to a random error in chromosomal division, called in technical jargon “non-disjunction”. This error can occur during the formation of reproductive cells and leads to the presence of an extra chromosome 13 already at the moment of conception.
From a genetic point of view, different forms are distinguished:
- Complete trisomy 13. The most frequent, in which all cells have three copies of chromosome 13. It is associated with the most complex clinical picture.
- Partial trisomy 13 or mosaicism. Only some cells have the extra copy of chromosome 13 while the rest have only the normal 2 copies. This form is compatible with a less severe condition and a higher life expectancy.
- Trisomy 13 by translocation. In a minority of cases (about 20%), trisomy 13 is due to a reorganization of the structure of the chromosomes (in technical jargon “Robertsonian translocation”) which may involve chromosome 13, which binds to another chromosome. This type of mutation can be inherited from a healthy carrier parent, increasing the risk of recurrence in subsequent pregnancies.
Risk factors and heredity
Trisomy 13 has an incidence of 1 in every 8,000-12,000 live births (if prenatal deaths are considered, the cases are many more) and occurs more frequently in females.
Advanced maternal age is a major risk factor for trisomy 13, although the condition can occur at any age. In the majority of cases the genetic event is sporadic and is never related to behavior or environmental factors.
The risk of recurrence in subsequent pregnancies is generally low. However, in cases where trisomy 13 is linked to a balanced translocation in one of the parents, the risk of a new diagnosis may be higher.
Genetic counseling is always indicated to support any type of diagnostic process and appropriate therapeutic decision, especially to clarify any possible doubts.
Symptoms and clinical manifestations of Trisomy 13
Trisomy 13 interferes with development already in the prenatal period, fetal growth is often reduced and multiple structural malformations are frequent. The most characteristic clinical manifestations include:
- craniofacial anomalies, such as microcephaly (reduced head circumference), holoprosencephaly (i.e. the incomplete separation of the two hemispheres of the brain), cleft palate (an incomplete formation of the palate), cleft lip (commonly known as “hare lip”).
- ocular abnormalities, including microphthalmia, i.e. smaller than normal eyes.
- anomalies of the hands and feet, in particular polydactyly, which involves the presence of more than five toes.
- Congenital heart defects, often associated with trisomies (at least in 70-80% of cases), can be more or less complex.
- disorders in the development of the central nervous system, most often associated with a very serious intellectual disability.
- anomalies of the urogenital system, this syndrome is frequently associated with polycystic kidney disease, cryptorchidism in males (failure of descent of one or both testicles into the scrotum) and uterus with two separate cavities in females.
- breathing problems, such as frequent episodes of apnea.
- hearing disorders, sometimes associated with deafness.
- Cutaneous aplasia, which is a rare congenital condition that involves the lack of skin layers, for example on the scalp, but also on the limbs or face.
The combination and severity of symptoms and pathologies associated with trisomy 13 vary depending on the genetic form, with generally milder conditions in the mosaic or partial forms compared to the complete form.
How Patau Syndrome is diagnosed
The diagnosis of Patau Syndrome can already occur prenatally and can be confirmed after birth.
Prenatal diagnosis
During pregnancy, trisomy 13 may be suspected in the presence of certain ultrasound signs. Ultrasound can highlight structural anomalies as early as the first trimester, such as major brain defects, complex heart disease or craniofacial malformations.
Non-invasive screening tests, such as the Bi-test and fetal DNA testing, can be useful, as in the case of trisomies 18 and 21, because they allow the risk of whether the fetus is affected or not to be estimated, but do not provide a certain diagnosis. The increase in the nuchal translucency value, however, and the presence of more ultrasound markers strengthen the clinical suspicion of the presence of the syndrome.
Subsequent diagnostic confirmation requires invasive tests, such as chorionic villus sampling or, if necessary, amniocentesis, which allow direct analysis of the fetal chromosomes, after taking a sample of placental tissue or amniotic fluid.
Post-natal diagnosis
After birth, the diagnosis can be confirmed through an objective examination and the evaluation of the physical characteristics of the newborn, whether or not they ascertain the characteristic clinical signs of the syndrome. Further confirmation of Patau syndrome occurs through the analysis of the karyotype on a blood sample, which allows the trisomy of chromosome 13 to be identified. Subsequently, instrumental tests such as echocardiogram, cerebral and abdominal ultrasound are necessary, to ascertain the presence or absence of internal congenital malformations and to take care of the child in the most appropriate way possible.
Treatment and care of the child
There is no cure for Patau Syndrome, the approach is multidisciplinary and is mainly based on palliative and supportive care, with the aim of guaranteeing the maximum quality of life for the child, even in difficult conditions.
In certain cases, surgical interventions may be considered, for example for some congenital heart defects or for cleft lip and palate, after a careful evaluation of the general conditions.
Therapies, such as physiotherapy and speech therapy, can help in managing motor and feeding difficulties, but also in respiratory complications, starting from the first months. Such complex syndromes require a different vision, starting from the first hours after birth, above all assistance that seeks to reduce the pain and burden due to more invasive procedures.
Prognosis and life expectancy
Survival in cases of trisomy 13, especially in the complete form, is unfortunately very limited. Mortality is high already in the perinatal period and in the first year of the child’s life. The main causes of death are linked to serious brain and heart malformations, as well as respiratory failure and a high risk of developing debilitating infections.
The cases of longer survival are always associated with mosaic forms, which however present with complex comorbidities. Scientific literature reports some cases, such as that of a girl who reached 12 years of age in which a mosaic form was observed due to new mutations that determined the presence of genetically normal cells.
Support for families
An essential part of the treatment process is psychological and emotional support for families, an aspect that cannot be neglected or separated from healthcare. Facing a diagnosis of Patau Syndrome means dealing with fears, uncertainties, complex choices and a significant emotional load, starting from pregnancy. Any word can be out of place, especially in the most negative diagnoses.
There are associations and support groups, as well as clinical centres, which can offer information, guidance on services and sharing experiences with other couples. The SOFT Italia association, for example, helps families with children with Patau Syndrome and Edwards Syndrome.
It is also important to know the rights and benefits provided, since Patau Syndrome (like Edwards Syndrome) is recognized by the National Health System as a rare disease and it is therefore possible to request exemption from the healthcare copay, to also guarantee the child and the family economic relief. Although these are very complicated situations to deal with, it is always a duty to offer children and families a quality of life that is as dignified as possible and involves as little suffering as possible.
