Non-Centromeric 18p Deletion

What is Non-Centromeric 18p Deletion?

18p deletion is a rare genetic syndrome is a deletion syndrome that presents with birth defects, intellectual disability and developmental delay. The severity of the syndromes depends on the size of the deletion. For reasons that are as yet unknown the syndrome tends to affect females more commonly than males.

There are two forms of the syndrome- centromeric and non-centromeric, and the type of deletion affects the type.

What gene changes cause Non-Centromeric 18p Deletion?

Non-Centromeric 18p Deletion is caused by a deletion of the short arm of chromosome 18. When this break does not occur at the centromere, Non-Centromeric 18 p deletion syndrome is diagnosed.

What are the main symptoms of Non-Centromeric 18p Deletion?

Symptoms may vary widely between individuals but the main symptoms of the syndrome include a short stature, low muscle tone and learning difficulties. Some individuals also struggle with communication and language development. A susceptibility to tooth decay, and a drooping of the upper eyelids is also common.

Other unique facial features of the syndrome include a flat and broad nasal bridge, a wide mouth, short philtrum and a small chin with low set ears and low hairline.

A small number of affected individuals have holoprosencephaly, which occurs when the two hemispheres of the brain fail to separate during in utero development. The condition is serious and in most cases life threatening.

Recurrent ear infections are a common symptom with subsequent hearing loss also reported.

Other symptoms include chronic constipation, hernias and issues with the spleen.

Affected individuals also seem to be more susceptible to anxiety disorders, as well as communication disorders and conditions related to motor skills delay.

How does someone get tested for Non-Centromeric 18p Deletion?

The initial testing for Non-Centromeric 18p Deletion 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 Non-Centromeric 18p Deletion

More than 150 cases with microscopically visible 18pter deletions have been reported. The del 18pter patients have short stature with variable facial dysmorphism such as round face, large ears, hypertelorism, flat nasal bridge, wide mouth with down-turned corners and single maxillary incisor. Notably 10% of cases have holoprosencephaly for which the putative HPE4 gene has been mapped to 18p11.3 (Overhauser et al., 1995). Gripp et al. (2000) reported 4 missense mutations in the TGIF gene in 268 patients with HPE. An adult female with a visible deletion 18p11.2->pter and partial trisomy for 2p25->pter was reported to have a normal intelligence (Horsley et al., 1998). Other familial microscopically visible 18p deletions have been reported (Tsukahara et al., 2001; Velagaleti et al., 1996; Uchida et al., 1965), some patients with normal or borderline intelligence have been observed.
A submicroscopic deletion was reported by Babovic-Vuksanovic et al., (2004). The patient had moderate mental delay, and developed schizophrenia in his adolescence. He had only mild dysmorphic features (hypertelorism, epicanthic folds, ptosis, round face, wide mouth and large, protruding ears).
Wester et al., (2006) performed a genotype - phenotype study in 7 patients with a cytogenetically visible 18p deletion, and found that a deletion of the region 18p11.1, in the centromeric region, all had mental retardation, while the ones with a more distal deletion (18p11.21) had a normal or borderline devlopment.
Turleau et. al. (2008) reviewed the clinical characteristics of 18p deletions, however, no distinctions between centromeric or non-centromeric were made.
Pachajoa (2016) described a ten year old female with a de novo ~12 Mb deletion of 18p11.32-p11.21. The girl showed developmental delay, long face, synophrys, prominent zygomatic arches, wide central incisors, dental pigmentation, hypoplastic left hemithorax, pectus excavatum, 5th finger clinodactyly, and 2-3 toe syndactyly.
Kumar et al. (2017) described a 45 year old woman with a movement disorder and a de novo 14.5 kB microdeletion in 18p11.32 region. Clinical characteristics included developmental delay, cognitive impairment, dysarthria, bilateral hip dysplasia, progressive deterioration in gait and balance, vertical supranuclear gaze palsy, hyperreflexia, craniofacial and lower limb dystonia, short stature, and microcephaly. Dysmorphic features were large, low-set and posteriorly rotated ears, hypertelorism, epicanthal folds, low posterior hairline, and ptosis. Brain MRI showed multifocal nonspecific subcortical T2 white matter hyperintensities.

* This information is courtesy of the L M D.
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