Tetrasomy 18p syndrome

Qu'est-ce que Tetrasomy 18p syndrome?

It is a rare chromosomal syndrome that affects multiple parts of the body. The main symptoms of the syndrome are usually very obvious in infancy and included difficulties with feeding, delayed development and intellectual disability. However these can vary according to the individual.

As a rare syndrome it is known to affect around 250 families worldwide.

This syndrome is also known as:
Isochromosome 18p Syndrome

Quelles sont les causes des changements génétiques Tetrasomy 18p syndrome?

The syndrome is caused because of the presence of an extra isochromosome 18p in each cell. This creates extra genetic material disrupts development within an affected individual and triggers the related syndromes.

Generally the syndrome is not inherited, except in very rare cases. It is the result of spontaneous mutations during the process of reproduction.

Quels sont les principaux symptômes de Tetrasomy 18p syndrome?

The main syndromes affecting infants with the syndrome include difficulties with feeding, frequent vomiting and a subsequent failure to gain sufficient weight. Symptoms in infancy might also include respiratory issues which affect breathing and jaundice.

Delayed development of motor skills (sitting, crawling and walking) is common with the syndrome. This can be caused by weak muscle tone, increased muscle tone or a stiffness known as spasticity.
Some affected individuals might also show symptoms that include ADHA, anxiety and other behavioural issues.
Unique facial features associated with the syndrome include low set ears, a small mouth, a flat philtrum (the area between the upper lip and nose), a thin upper lip and a high arched palate. A cleft palate may also be present.
Seizures, constipation, an abnormal curving of the spine are also possible symptoms.

Possible clinical traits/features:
Scoliosis, Microcephaly, Seizure, Thin vermilion border, Cognitive impairment, Gait disturbance, Hypertonia, Long philtrum, Low-set, posteriorly rotated ears, Large hands, Short nose, Narrow mouth, Abnormality of neuronal migration, Facial asymmetry, Epicanthus, Downslanted palpebral fissures

Comment quelqu'un se fait-il tester pour Tetrasomy 18p syndrome?

The initial testing for Thanatophoric dysplasia 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.

Informations médicales sur Tetrasomy 18p syndrome

Tetrasomy 18p is a rare chromosome abnormality. Clinical characteristics include developmental delay, feeding difficulties, neonatal jaundice, recurrent otitis media, abnormal muscle tone, chronic constipation, congenital orthopedic abnormalities, gastroesophageal reflux, cardiac defects, respiratory distress, and seizures (Sebold et al., 2010). All cases reported have been monocentric, implying that the isochromosome arises as a result of two independent events: nondisjunction and centromeric misdivision. The parental origin of the isochromosome has been reported to be maternal (Bugge et al., 1996; Eggerman et al., 1996; Kotzot et al., 1996)

Clinical features associated with tetrasomy 18p include congenital defects such as palate abnormality, heart abnormalities, orthopedic abnormalities and myelomeningocele. The neonatal period is complicated by feeding problems, respiratory problems and jaundice (Sebold et al., 2010).

PREVALENCE: 1/625,000
LIFE EXPECTANCY: There are no data indicating a reduced life expectancy
PRENATAL PRESENTATION: Abnormal amniocentesis

ASSOCIATED GENES: No individual genes have been linked to specific aspects of the phenotype
RECURRENT MUTATION(S): 96% are non-mosaic for an isochromosome with no duplication of 18q material; 2.5% have a duplication of q arm material as a part of the abnormal chromosome and another 2.5% are mosaic for the typical isochromosome

Development: The average full scale IQ score is 48 (37% in the mild range, 37% moderate, and 26% in the severe-to-profound range). Mean age when: walking independently at 33 months, saying single words at 28 months and 2-3 word phrases at 66 months.
Behavior/mood changes: Children - Problems with functional communication (97%), activities of daily living (91%), attention problems (61%), hyperactivity (54%); Adults – Problems with functional communication (62%), activities of daily living (62%), hyperactivity (54%)
Executive Function: Children – Problems with working memory (95%), task monitoring (90%), inhibiting (85%), initiating (70%), planning/organizing (70%), shifting (60%), emotional control (50%); Adults – Problems with working memory (93%), initiating (71%), inhibiting (64%), shifting (64%), planning/organizing (64%), task monitoring (50%)
Social Impairment: Children and Adults – Problems with social cognition (91%), restricted interests and repetitive behaviors (91%), social awareness (82%), social communication (73%), social motivation (55%)
Cardiac abnormalities: 47% (Most common: PDA 17%, VSD 14%, , PFO 7%, ASD 5% and less reported: pulmonary valve stenosis, hypoplastic transverse aortic arch, right ventricular hypertrophy and valve abnormalities)
Endocrinology: Underweight <3%ile 19%, growth hormone deficiency 12%
ENT: Recurrent otitis media 57%, hearing loss 32% (conductive, sensorineural or mixed), narrow ear canals 42%
Gastrointestinal: Constipation 81%, gastroesophageal reflux 36%, hernias 12%, pyloric stenosis 5%
Genitourinary: Cryptorchidism 63%, urinary tract anomalies 28% (horseshoe kidney and bladder diverticuli, small kidney, renal cyst, hydronephrosis, vesicoureteral reflux varying degrees), hypospadias 7%
Immunology/Rheumatology: Food allergies 33%, asthma 9%, Autoimmune: one person with hypothyroidism, one celiac, two with arthritis
Neonatal complications: 98% (feeding difficulties 83%, jaundice 57%, respiratory distress 31%)
Neurology: Abnormal muscle tone 98% (hypotonia 50%, mixed tone 28%, hypertonia 19%), brain MRI variants 58% (thin/hypoplastic corpus callosum, enlarged ventricles, white matter intensity changes, periventricular leukomalacia, Chiari malformation, choroid plexus cyst), seizures 54% (febrile 33%), myelomeningocele 7%
Ophthalmology: Strabismus 75%, refractive errors 71% (myopia 17%, hyperopia 33%, astigmatism 25%)
Orthopedic: Osteopenia (low mineral bone density) 100% of those assessed, scoliosis/kyphosis 53%, pes planus 49% , club foot 14%, metatarsus adductus 5%, rocker bottom feet 5%, vertical talus 5%
Skin: Eczema 21%
Dysmorphic features: Smooth philtrum 87%, palate anomalies 81% (high, arched, narrow), clinodactyly 61%, camptodactyly 58%, pointed chin 55% , small mouth 55%, microcephaly 74%, small ears 52%, abnormal columella 48%, gap between 1st and second toe 39%, ptosis 13%, dental crowding 19%

Sebold et al., (2010) described the clinical and molecular characteristics of 42 patients with tetrasomy 18p. Clinical characteristics include developmental delay, feeding difficulties, neonatal jaundice, recurrent otitis media, abnormal muscle tone (in order of frequency: hypotonia, mixed muscle tone and hypertonia), chronic constipation, congenital orthopedic abnormalities (congenital hip dysplasia and clubfoot, mainly), gastroesophageal reflux, cardiac defects (most frequently patent ductus arteriosus and ventricular septal defect), respiratory distress, and seizures (febrile seizures). Most frequent dysmorphic features were smooth philtrum, high arched and narrow palate, clinodactyly, camptodactyly, prominent and/or pointed chin, small mouth, small ears, sloping shoulders and abnormal columella.

O’Donnell et al., (2015) described the intellectual and behavioral characteristics of persons with tetrasomy 18p. This is a more detailed investigation into the cognitive and behavioral characteristics of previously reported data from Sebold et al., (2010). This paper evaluated intellectual functioning using standard measures of cognitive ability, measures of executive function, adaptive and maladaptive behaviors. Intellectual abilities ranged from mild impairment/borderline normal to severe/profound impairment, calling into question the assumption that severe cognitive limitation is always a feature of tetrasomy 18p. For persons with tetrasomy 18p with mild cognitive deficits, the main barriers to successful functioning stem from limited social and metacognitive skill development and behavior regulation problems, rather than being solely determined by cognitive deficits alone.

Inan et al., (2016) described two female dichorionic diamniotic twin fetuses with tetrasomy 18p. Clinical characteristics of twin A were intrauterine growth retardation (IUGR), omphalocele, kyphosis, and unilateral leg and foot deformity. Twin B showed IUGR, atrial septal defect, ventricular septal defect, short and cleft right great toe, retrognathia, malformed low-set ears, unilateral mild talipes, long philtrum, flat nasal bridge and hypertelorism.

Karimzad Hagh et al., (2017) described a prenatal diagnosis of tetrasomy 18 in a female fetus without reporting ultrasonographic findings. Karyotype revealed 47,XX,+mar dn[36]/46, XX[4], and FISH showed sSMC as i(18)(pter- >q11.1: q11.1- >pter). The pregnancy was terminated, and an autopsy was performed. Clinical characteristics included low anterior hairline, large philtrum, mild retrognathia, low-set and posteriorly rotated ears with prominent antihelix, joint contracture of the lower limbs, long and narrow toes with clinodactyly of the 1st and 5th toes, and one hand with postaxial polydactyly.

Monitor for scoliosis and kyphosis
Monitor for low bone mineral density

Genetics evaluation and counseling
Referral for developmental services and therapy
Audiology/ENT evaluation for hearing problems
Cardiology for cardiac abnormalities
Endocrinology evaluation for short stature, including evaluation of growth hormone deficiency, thyroid levels and vitamin D
Gastroenterology for chronic and severe constipation and gastroesophageal reflux management
Immunology/Rheumatology for evaluation of atopic disorders (food allergies, asthma, eczema)
Neurology evaluation for management of seizures
Nutritional evaluation for failure to thrive
Ophthalmology evaluation for vision problems
Orthopedic evaluation for management of foot abnormalities
Renal ultrasound to exclude kidney malformations or functional problems (reflux)


Chromosome 18 Registry and Research Society

(1) Chromosome 18 Clinical Research Center
UT Health Science Center, MSC 7820
7703 Floyd Curl Drive San Antonio, TX 78229
[email protected]
(210) 567-5231

décembre 16, 2018

* 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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