Trisomy 18, known as Edwards syndrome, is a chromosomal disease caused by the presence of an additional copy of chromosome 18. This anomaly has serious consequences on prenatal development, up to the death of the fetus in utero in a "high percentage of cases. trisomy 18 affects approximately one in 6,000 - 8,000 live births.
Children with Edwards syndrome have pre- and postnatal developmental delay, a characteristic appearance, malformations of the skull, limbs and internal organs. About half of affected infants are no older than two weeks and only one in five reaches three months. About one in 10 live births survive beyond a year, with severe physical and mental disabilities. Survival to adulthood is very rare.
There is currently no specific therapy for trisomy 18, but only supportive interventions for the various clinical manifestations. (see Therapy section)
Caring for a child with Edwards syndrome takes a lot of physical and psychological commitment. Most family members / carers need appropriate social and health support.
In Italy, trisomy 18 is included in the "list of rare diseases exempt from the cost of the ticket (Decree of the President of the Council of Ministers of 12 January 2017, Annex 7) with the code RNG080, which refers to the group" Syndromes of chromosomal aneuploidy For other information (eg diagnosis and treatment centers, patient associations, etc.) on trisomy 18, it is possible to contact the Rare Diseases Toll-Free Telephone (TVMR) 800.89.69.49. The number is active from Monday to Friday from 9:00 am at 13:00.
Children with trisomy 18 have complex and variable signs and symptoms, such as:
- severe growth failure and feeding difficulties with poor suction
- remarkably small head (microcephaly), with elongated and narrow shape (dolichocephaly)
- low set ears
- eye malformations (coloboma, microphthalmia)
- small mouth and jaw (micro-retrognathia)
- long fingers that overlap, clenched fist with index superimposed on the middle finger (hooked)
- club foot (toe pointing down) or to ice ax
- heart defects
- gastrointestinal malformations (esophageal, anorectal atresia, omphalocele)
- genitourinary malformations
- hypotonia and psychomotor retardation
Other signs and symptoms that may arise are:
- malformations of the palate (cleft lip and palate)
- difficulty in breathing
- bone abnormalities
- lung and urinary tract infections
- malformations of the brain and spinal cord
The extra chromosome 18 (supernumerary) is present due to a separation error (non-disjunction) of the chromosomes, the cause of which remains little known today. The error occurs in the segregation phase of the chromosomes during meiosis or post-zygotic division.
In most cases, the anomaly is of maternal origin: the paired chromosomes did not separate correctly during meiosis of the maternal gamete.Therefore, when the maternal and paternal gamete merge in conception, the embryo will have an excess of chromosome 18.
In a small percentage of cases in which the extra chromosome is of paternal origin, the nondisjunction error occurs in the post-zygotic phase.
The frequency of maternal nondisjunction defects responsible for trisomy 18 as well as other chromosomal abnormalities (eg trisomy 21) are correlated with maternal age and increase as the mother ages.
There are 3 main types of trisomy 18:
- complete form, approximately 94% of children with Edwards syndrome have the complete form, meaning each cell in the body has three copies of chromosome 18, instead of two. Most babies with this form die early
- mosaic trisomy, about 5% of children with Edwards syndrome have the extra copy of chromosome 18 in only certain cells of the body. This less severe form of the disease is known as mosaic trisomy 18. The severity of the signs and symptoms of mosaic disease depends on the type and number of cells that have the extra chromosome. Some children may be affected only mildly by the disease, while others are very severely. About 7 children with mosaic trisomy for every 10 live births reach at least the first year of age and, in rare cases, can survive to young adulthood.
- partial form, in this form, the least frequent among the types of trisomy 18, to be tripled is only a segment of chromosome 18. The tract and the extension of the segment concerned are responsible for the variability of expression of the disease
Trisomy 18 Diagnosis During Pregnancy
A possible trisomy 18 can be suspected from the first control ultrasounds since the fetus has very evident anomalies from the first months of pregnancy.
The screening test, which is usually done between the 11th and 14th week of gestation, known as a combined test, includes a specific blood test and the nuchal translucency test (a "targeted ultrasound to look for skin thickening in the skin). back of the baby's neck). This test is also used to diagnose other chromosomal abnormalities such as Down syndrome and Patau syndrome.
Around the 20th week of gestation, morphological ultrasound is performed for a complete evaluation of all the anatomical areas of the fetus, in order to exclude or ascertain fetal malformations.
Amniocentesis remains the main investigation for the study of fetal chromosomes and the prenatal diagnosis of chromosomal aneuploidies (anomalies in number). Performed around the 16th-18th week, it allows the collection of amniotic fluid from the uterine cavity through the abdominal wall. The amniotic fluid contains fetal cells which are cultured and subsequently analyzed with suitable cytogenetic methods.
The villocentesis, or chorionic villus sampling, is a more invasive prenatal diagnosis technique than amniocentesis. It is performed earlier than amniocentesis, around the 10th-11th week, and consists in the transabdominal sampling and under ultrasound control of tissue trophoblastic, containing fetal cells. A "direct chromosomal analysis can be performed on the sample or as in the case of amniotic fluid, the cells are cultured and subsequently analyzed. For the disadvantages associated with this technique (eg invasiveness, risk of abortion, difficulty with chromosomal mosaicisms)" , is not considered by many to be the technique of choice for the diagnosis of chromosomal aneuploidies.
Recently, a test has been developed that involves the analysis of fetal DNA (non-invasive prenatal screening based on DNA), obtained from a maternal blood sample from the 10th week onwards, on which it is possible to carry out cytogenetic and molecular tests. The test is not diagnostic but probabilistic, therefore any positive result must be confirmed with the execution of the traditional invasive investigation (villocentesis and amniocentesis).
To find out more, consult the prenatal diagnosis page.
There is no specific therapy for trisomy 18. The care and management of children with trisomy 18 requires the involvement of a multidisciplinary team of specialists.
Supportive treatment should be particularly aimed at problems that seriously endanger the child's life, such as infections and heart defects.
If the child has difficulty in feeding it will be necessary to resort to artificial feeding. Movement difficulties and alterations in muscle tone are mainly treated with physiotherapy.
NHS. Pregnancy (English)
SOFT Italy Association
Cromosoma 18 Italy registry association (A.Ge.Mo 18). Trisomy 18