Trisomy 18 syndrome

What is Trisomy 18 syndrome?

Also known as Edwards syndrome, it is a rare chromosomal syndrome that presents with anomalies and symptoms that affect many parts of the body. Due to the severity of symptoms many infants with the condition die before birth or in the first month of life. The 5-10% of children who survive the first year have severe intellectual disability. The risk of having a child with the syndrome increases with the age of the mother.

This syndrome is also known as:
Edward's syndrome Hyp Hypophosphatemia, X-linked; Xlh Hypophosphatemic Vitamin D-resistant Rickets; Hpdr Vitamin D-resistant Rickets, X-linked

What gene changes cause Trisomy 18 syndrome?

The syndrome is caused by the presence of three copies of chromosome 18 in each cell rather than two. In the 5% of people with an extra chromosome 18 in just some of the cells of the body they have a form of the condition known as mosaic trisomy 18.

The majority of cases occur as the result of random events during the reproductive process. It is usually not inherited.

What are the main symptoms of Trisomy 18 syndrome?

The main symptoms of the syndrome include slow growth before birth with a subsequent low birth weight.

Physical features of the syndrome include a small head, an abnormally shaped head, small jaw and mouth and fists that are clenched with overlapping fingers.

Congenital heart defects and organ abnormalities are common and are usually diagnosed before birth. These serious medical conditions contribute to the short life expectancy of infants with the syndrome, many of whom do not survive birth.

In the small number of infants with the syndrome who survive the first year, intellectual disability is a major symptom of the condition.

Possible clinical traits/features:
Abnormality of dental enamel, Enthesitis, Elevated alkaline phosphatase, Elevated circulating parathyroid hormone level, Craniofacial hyperostosis, Femoral bowing, Fibular bowing, Renal phosphate wasting, Phenotypic variability, Spinal canal stenosis, X-linked dominant inheritance, Trapezoidal distal femoral condyles, Premature loss of teeth, Hypophosphatemic rickets, Shortening of the talar neck, Tibial bowing, Recurrent fractures, Spinal cord compression, Frontal bossing, Abnormal concentration of calcium in blood, Abnormality of the metaphysis, Abnormality of pelvic girdle bone morphology, Bowing of the legs, Bone pain, Arthralgia, Renal tubular dysfunction, Osteoarthritis, Osteomalacia, Hearing impairment, Short stature, Genu varum, Flattening of the talar dome, Metaphyseal irregularity, Hypophosphatemia, Hypomineralization of enamel

How does someone get tested for Trisomy 18 syndrome?

The initial testing for Trisomy 18 syndrome can begin with facial analysis screening, through the FDNA Telehealth telegenetics platform, which can identify the key markers of the syndrome and outline the need for further testing. A consultation with a genetic counselor and then a geneticist will follow.

Based on this clinical consultation with a geneticist, the different options for genetic testing will be shared and consent will be sought for further testing.

Medical information on Trisomy 18 syndrome

Trisomy 18 was described by Edwards et al. (1960) and Smith et al (1960). This the second most common autosomal trisomy after trisomy 21 in liveborn children.
This chromosomal trisomy is characterized by severe psychomotor and growth retardation, microcephaly, microphthalmia, microstomia, micrognathia, short sternum, clenched fingers and multiple additional congenital malformations.
A seven-year-old boy reported by Demir et al., (2005) had a cleft lip and palate, a Klippel-Feil anomaly and conductive deafness. A CT scan revealed two narrow bony canals.
Weon et al., (2007) reported a single case with developmental delay and profound deafness at 28 months. He had microtia, a unilateral, slightly small ear canal on one side, and bilateral duplication of the ear canals, as shown on MRI. The cochlea was normal. The lateral and superior semicircular canals appeared bulbous and enlarged,and the oval windows were absent.
Kew and Abdullah (2012) reported a man with unilateral sensorineural hearing loss, a facial nerve palsy, and ipsilateral duplication of the interior auditory canal. Radiologically, there was aplasia of the vestibulocochlear nerve.
Imataka et al. (2016) retrospectively described clinical features and survival in 44 individuals with trisomy 18 who received intensive care treatments. The average birth weight was 1585.5±493.6 g. Congenital heart disease was observed in 95% of patients including VSD in 37 patients, PDA in 17 patients, ASD in 14 patients, coarctation of the aorta in 8 patients, double outlet right ventricle in 6 patients, endocardial cushion defect in 3 patients, tricuspid atresia in 2 patients, tetralogy of Fallot TOF in 2 patients, mitral valve atresia in 2 patients, transposition of great arteries and hypoplastic left heart syndrome in 1 patient. Among the major central nervous malformations, 4 patients had complicated brain or spinal anomaly (two had spinal meningocele, 1 had holoprosencephaly and 1 had Dandy-Walker malformation). Esophageal atresia was present in 16 individuals and umbilical hernia in 4 individuals.
Dereddy et al. (2016) described the outcome of 29 live-born patients with trisomy 18. Clinical characteristics included central nervous system anomalies (in order of frequency: microcephaly, posterior fossa cyst, cerebellar abnormalities, agenesis of corpus callosum, myelomeningocele and encephalocele), cardiovascular abnormalities (including: ventricular septal defect, atrial septal defect, double outlet right ventricle, hypoplastic left heart, Shone’s complex, coarctation of the aorta, unbalanced atrioventricular canal defect, and Tetralogy of Fallot), genitourinary anomalies (multicystic kidney, renal agenesis, undescended testes), and tracheoesophageal fistula.
Correia et al. (2016) described eye anomalies in four patients (from a cohort of 31) with trisomy 18, including corneal opacities, cataract, microphthalmia, retinal folds, Peters anomaly, anophthalmia, iridocorneal adhesions, short and slanting palpebral fissures, inner epicanthic folds, ptosis, sparse or abnormally long eyelashes, abnormally thick lids, and blepharophimosis.
Cammarata-Saclisi et al. (2017) described five patients (four females and a male) with mosaic trisomy 18. Percentage of mosaic varied between 9 to 70% in peripheral blood cells.

* This information is courtesy of the L M D.
If you find a mistake or would like to contribute additional information, please email us at: [email protected]

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