Tetrasomy 18p

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Tetrasomy 18p is a chromosomal condition that affects many parts of the body. This condition usually causes feeding difficulties in infancy, delayed development, intellectual disability that is often mild to moderate but can be severe, changes in muscle tone, distinctive facial features, and other birth defects. However, the signs and symptoms vary among affected individuals.

Babies with tetrasomy 18p often have trouble feeding and may vomit frequently, which makes it difficult for them to gain weight. Some affected infants also have breathing problems and jaundice, which is a yellowing of the skin and the whites of the eyes.

Changes in muscle tone are commonly seen with tetrasomy 18p. Some affected children have weak muscle tone (hypotonia), while others have increased muscle tone (hypertonia) and stiffness (spasticity). These changes contribute to delayed development of motor skills, including sitting, crawling, and walking.

Tetrasomy 18p is associated with a distinctive facial appearance that can include unusually shaped and low-set ears, a small mouth, a flat area between the upper lip and the nose (philtrum), and a thin upper lip. Many affected individuals also have a high, arched roof of the mouth (palate), and a few have had a split in the roof of the mouth (cleft palate).

Additional features of tetrasomy 18p can include seizures, vision problems, recurrent ear infections, mild to moderate hearing loss, constipation and other gastrointestinal problems, abnormal curvature of the spine (scoliosis or kyphosis), a shortage of growth hormone, and birth defects affecting the heart and other organs. Males with tetrasomy 18p may be born with undescended testes (cryptorchidism) or the opening of the urethra on the underside of the penis (hypospadias). Psychiatric conditions, such as attention-deficit/hyperactivity disorder (ADHD) and anxiety, as well as social and behavioral challenges have also been reported in some people with tetrasomy 18p.

Inheritance

From: MedlinePlus Genetics, National Library of Medicine

Not inherited

Understanding terms used in the source

These definitions explain medical words used above. A definition is not evidence that another condition is present, and it does not predict how a symptom will develop. Ask the clinician which terms apply to the actual examination or test result.

Feeding difficulties in infancy

Impaired feeding performance of an infant as manifested by difficulties such as weak and ineffective sucking, brief bursts of sucking, and falling asleep during sucking. There may be difficulties with chewing or maintaining attention.

Recurrent ear infections

Increased susceptibility to ear infections as manifested by recurrent episodes of ear infections.

Intellectual disability

The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence.

Feeding difficulties

Impaired ability to eat related to problems gathering food and getting ready to suck, chew, or swallow it.

Cryptorchidism

Testis in inguinal canal. That is, absence of one or both testes from the scrotum owing to failure of the testis or testes to descend through the inguinal canal to the scrotum.

When it may begin

From: MedlinePlus Genetics, National Library of Medicine

This condition usually causes feeding difficulties in infancy, delayed development, intellectual disability that is often mild to moderate but can be severe, changes in muscle tone, distinctive facial features, and other birth defects. Some affected infants also have breathing problems and jaundice, which is a yellowing of the skin and the whites of the eyes.

Inheritance in the source

From: MedlinePlus Genetics, National Library of Medicine

Not inherited

Which doctor should you see?

The suggested department for discussing Tetrasomy 18p is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Tetrasomy 18p. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.