History
Prenatal history in trisomy 18
See the list below:
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Maternal polyhydramnios possibly related to defective sucking and swallowing reflexes in utero
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Oligohydramnios secondary to renal defects
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Disproportionately small placenta
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Single umbilical artery
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Weak fetal activity
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Fetal distress
Clinical history in trisomy 18
See the list below:
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Apneic episodes
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Poor feeding
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Marked failure to thrive
Physical
See the list below:
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Neurological
Delayed psychomotor development and mental retardation (100%)
Neonatal hypotonia followed by hypertonia, jitteriness, apnea, and seizures
Malformations (eg, microcephaly, cerebellar hypoplasia, meningoencephalocele, anencephaly, hydrocephaly, holoprosencephaly, Arnold-Chiari malformation, hypoplasia or aplasia of the corpus callosum, defective falx cerebri, frontal lobe defect, migration defect, arachnoid cyst, myelomeningocele)
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Cranial - Microcephaly, elongated skull, narrow bifrontal diameter, wide fontanels, and prominent occiput
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Facial - Microphthalmia, ocular hypertelorism, epicanthal folds, short palpebral fissures, iris coloboma, cataract, corneal clouding, abnormal retinal pigmentation, short nose with upturned nares, choanal atresia, micrognathia or retrognathia, microstomia, narrow palatal arch, infrequent cleft lip and cleft palate, preauricular tags and low-set, and malformed ears (faunlike with flat pinnae and a pointed upper helix)
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Skeletal - Severe growth retardation, characteristic hand posture (ie, clenched hands with the index finger overriding the middle finger and the fifth finger overriding the fourth finger), camptodactyly, radial hypoplasia or aplasia, thumb aplasia, syndactyly of the second and third digits, arthrogryposis, rocker-bottom feet with prominent calcanei, talipes equinovarus, hypoplastic nails, dorsiflexed great toes, short neck with excessive skin folds, short sternum, narrow pelvis, and limited hip abduction
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Cardiac
More than 90% of infants with trisomy 18 have cardiac malformations.
The most common abnormalities are ventricular septal defects with polyvalvular heart disease (pulmonary and aortic valve defects)
Other cardiac malformations include atrial septal defects, patent ductus arteriosus, overriding aorta, coarctation of aorta, hypoplastic left heart syndrome, tetralogy of Fallot, and transposition of great arteries.
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Pulmonary -Pulmonary hypoplasia and abnormal lobation of the lung
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GI -Omphalocele, malrotation of the intestine, ileal atresia, common mesentery, Meckel diverticulum, esophageal atresia with or without tracheoesophageal fistula, diaphragmatic eventration, prune belly anomaly, diastasis recti, absent gallbladder, absent appendix, accessory spleens, exstrophy of Cloaca, pyloric stenosis, imperforate or malpositioned anus, pilonidal sinus, and hernias (ie, umbilical, inguinal, diaphragmatic)
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Genitourinary
Micromulticystic kidneys, double ureters, megaloureters, hydroureters, hydronephrosis, horseshoe kidneys, and unilateral renal agenesis
Cryptorchidism, hypospadias, and micropenis in males
Hypoplasia of labia and ovaries, bifid uterus, hypoplastic ovaries, and clitoral hypertrophy in females
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Endocrine - Thymic hypoplasia, thyroid hypoplasia, and adrenal hypoplasia
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Dermal (ie, dermatoglyphics) - Increased number of simple arches on the fingertips, transverse palmar crease, increased atd angle, and clinodactyly of the fifth fingers with a single flexion crease
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Phenotypic spectrum of mosaic trisomy 18 [17]
Phenotype of individuals with mosaic trisomy 18 varies widely. Some individuals who have the complete trisomy 18 (typical Edwards syndrome) phenotype experience early death whereas others are phenotypically completely normal. The latter group is exemplified by several normal-appearing adults with mosaic trisomy 18 who were identified only after giving birth to children with complete trisomy 18.
Anomalies vary widely, most at low frequencies, including microcephaly, delayed bone age, brachydactyly, congenital heart defects, developmental delay, short stature, and premature ovarian failure.
Intellectual capabilities range from profound intellectual disability to above-average intelligence. No correlation between the percentage of trisomic cells in either fibroblasts or leukocytes and the individual’s phenotype or intellectual function is noted.
Causes
See the list below:
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Full trisomy 18 is responsible for 95% of Edwards syndrome cases. Mosaicism and translocations cause few cases. An extra chromosome 18 is responsible for the phenotype.
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The incidence rate increases with advanced maternal age. In approximately 90% of cases, the extra chromosome is maternal in origin, with meiosis II errors occurring twice as frequently as meiosis I errors. This is in contrast to other human trisomies, which exhibit a higher frequency of nondisjunction in maternal meiosis I. Among cases resulting from paternal nondisjunction, most are the result of postzygotic mitotic errors.
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Although full trisomy results from meiotic nondisjunction, mosaic trisomy is due to postzygotic mitotic nondisjunction. Mosaic trisomy 18 occurs when both a trisomy 18 cell line and a normal cell line are present in the same individual. Mosaic trisomy 18 accounts for approximately 5% of trisomy 18 cases. [18] The clinical phenotype varies depending on the level of mosaicism and the tissue involved and ranges from the complete trisomy 18 phenotype to no dysmorphic features and normal intelligence. [19]
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Translocation trisomy gives rise to partial trisomy 18 syndrome. Partial trisomy 18 occurs when a segment of chromosome 18 is present in triplicate, often resulting from a balanced translocation carried by one parent. It accounts for approximately 2% of trisomy 18 cases.
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The smallest extra region necessary for expression of serious anomalies of trisomy 18 appears to be 18q11-12.
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Note the microphthalmia, micrognathia/retrognathia, microstomia, low-set/malformed ears, short sternum, and abnormally clenched fingers in an infant with trisomy 18 (Edwards syndrome).
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This photo depicts the elongated skull, prominent occiput, low-set ear, micrognathia/retrognathia, short neck, and characteristic finger-grasping pattern in an infant with trisomy 18 (Edwards syndrome).
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Note the characteristic clenched hand of trisomy 18 (Edwards syndrome) with the index finger overriding the middle finger and the fifth finger overriding the fourth finger.
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This photo demonstrates a G-banded karyotype showing 47,XY,+18.
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Note the rocker-bottom foot with a prominent calcaneus in an infant with trisomy 18 (Edwards syndrome).
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This photo shows the hands of a fetus with trisomy 18 (Edwards syndrome). Note that hands typically present with overlapping digits, in which the second and fifth fingers override the third and fourth fingers, respectively. The overall posturing of the wrists and fingers in this fetus is suggestive of contractures.
