18q - Deletion: An Overview

Introduction

18q deletion is a genetic disorder caused due to absent or missing genes from chromosome 18. This disorder is caused due to a genetic error called deletion. The other names for 18q deletion are deletion 18q syndrome, monosomy 18q, 18q monosomy, and chromosome 18 deletion syndrome. Gene deletion in chromosome 18 ranges from small to large deletions. Therefore, the severity of symptoms of this disorder in large deletion is higher in comparison to small deletion. Individuals suffering from this disorder have distinctive facial appearances, delayed growth, and intellectual abilities and are also retarded regarding growth.

What Is Meant by Chromosomal Aberrations?

Chromosomal aberrations explain structural and numerical abnormalities. The chromosomal mutation is the other name for chromosomal aberration. Structural changes or abnormalities are called structural aberrations, and numerical changes or abnormalities are called ploidy changes or numerical aberrations. Structural aberrations comprise the errors in which a chromosome or gene segment is extra, lost, or located in another region (translocated). Chromosomal aberrations have been classified into four types, namely:

• Deficiency or deletion.

• Duplication.

• Inversion.

• Translocation.

What Is the Deletion Type of Chromosomal Aberration?

Deletion can be defined as a chromosomal aberration type in which a chromosome segment and its genes are missing. Deletion is of the following four types, namely:

• Terminal Deletion: In terminal deletion, the segment of chromosomes or genes is missing from the terminal part with a single break.

• Intercalary Deletion: It describes the type of genetic error in which the segment of a chromosome or the genes are missing from the between. Two breaks in the segment can be identified in such a kind of deletion error.

• Homozygous Deletion: It describes the loss of chromosome segments or genes from the homologous chromosome pair.

• Heterozygous Deletion: Heterozygous deletion represents the loss of chromosomal segments or genes from any homologous chromosome pair.

As stated above, deletion is the type of genetic error in which loss of genetic material and loss of genes are associated with deleterious effects. This error is expressed with various signs and symptoms for every genetic disorder.

How Is 18q Deletion Caused?

18q deletion disorder is caused by to deletion of genetic material in chromosome 18 in the distal part of the long arm q. In most cases, the deletion of genetic material is noted in the terminal end of chromosome 18. More significant deletion shows more complex features than more minor deletion errors. Multiple genes are lost in this type of genetic error. At present, all genes are not studied. Researchers are working extensively on identifying the genes responsible for the disorder. Chromosomes are present in the nucleus of a cell present in the entire body of an individual. They are responsible for distinct characteristics in every individual. Each chromosome has two arms, one short and the other long. The short arm is denoted as p, and the long arm is denoted by the letter q. Deleting the genetic material generally occurs due to a spontaneous error and is mostly not inherited.

Is 18q Deletion Disorder Inherited?

18q deletion disorder is not an inherited disorder, and it is caused due to genetic error. This occurs due to a random error during the reproductive cell's production of eggs and sperm or early fetal development. Affected people have no history of a similar disorder in the past, but they may pass this chromosomal deletion to their children. Five to ten percent of individuals even inherit these chromosomal deletion errors from parents unaffected by 18q deletion disorder. Structural chromosomal aberrations are responsible for the development of these genetic disorders. These chromosomal abnormalities produce symptoms that are typical of this genetic error.

What Are the Clinical Features of the Genetic Disorder Due to Deletion Mutation?

The following are the most commonly reported general clinical features:

• Delayed growth.

• Altered development of speech.

• Motor skills such as sitting and standing are affected, which causes difficulty in carrying out daily activities.

• Attention deficit hyperactivity disorder is a commonly noted feature in 18q deletion. It is a neurodevelopmental disorder diagnosed in childhood and continues up to adulthood. Children suffering from this disorder have difficulty concentrating, get easily distracted, and have delayed thinking abilities. They have difficulty learning the alphabet, spelling, and mathematical tables.

• Compulsive behavior, such as shredding papers, is expected to alter behavior in these children.

• As seen in autism, impaired socializing skills are also noted in these children.

• Few individuals also suffer from heart and kidney disorders.

The following are a few distinctive features reported in individuals suffering from genetic disorders due to deletion:

• The back of the head appears to be flat.

• Hypertelorism (widely spaced eyes are commonly noted).

• The eyelid fold is slanted upward.

• Eyebrows have a high arch appearance.

• The midfacial region of the individual is generally flat in appearance.

• A short nose and flat nasal bridge are characteristic features in these individuals.

• Widened philtrum over the lips.

• Small lower jaw.

• Abnormally protruded lips.

• Ears are malformed.

• The palate has a high arch appearance.

• Short-statured

• These individuals are mostly obese.

The genetic disorders caused due to deletion errors, namely, 6q deletion, 11q deletion,18q deletion, 13q deletion, and 9p deletion, portray more or less similar characteristics, including delayed growth, retarded intellectual status, and distinctive facial appearance.

What Are the Management Protocols for 18q Deletion Disorder?

Researchers are working to search for a definite treatment protocol for this disorder. The doctors focus on providing symptomatic relief that eases these individuals' daily activities. Psychiatrists aim to reduce the symptoms of behavioral disorders and improve these individuals' socializing skills. Physiotherapists seek to improve the motor skills of these individuals. So that they can sit, stand, and walk without any secondary support or minimum assistance. Dental practitioners aim to improve individuals' oral hygiene to reduce the caries rate. Specialized doctors treat individuals with severe signs and symptoms, including heart and kidney disorders, with utmost care.

Conclusion:

18q deletion disorder is a rare genetic disorder caused by to deletion of genetic material in chromosome 18’s long arm q. The signs and symptoms vary widely; thus, clinicians should thoroughly examine the patients. Solid treatment and protocol are unavailable, but various research is going on in medical genetics to treat this disorder. Genetic mapping and targeted gene therapy are extensively studied for their application in diagnosing and treating rare genetic disorders like 18q deletion.