9p Deletion- Absent Genes on Chromosome 9

Introduction

9p deletion is a genetic disorder caused by missing or absent genes on chromosome 9. A genetic error named deletion is noted to be responsible for this disorder. The other names for 9-p deletion are 9p partial monosomy, distal monosomy, and monosomy. Gene deletion on chromosome 9 ranges from small to large deletions. Therefore, the severity of this symptom is less in comparison to a small deletion. 9p deletion is a genetic error more frequently noted in females than in males.

What Is Meant by Chromosomal Aberrations?

Structural and numerical abnormalities in genetic expression are known as chromosomal aberrations. Chromosomal mutation is another name for chromosomal aberration. Structural aberrations stand for changes or abnormalities in the structural buildup of any genetic constituent, 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). Researchers have divided chromosomal aberrations into four types, namely:

• Deficiency or deletion.

• Duplication.

• Inversion.

• Translocation.

What Is the Deletion Type of Chromosomal Aberration?

Deletion is a type of chromosomal aberration in which a segment of the chromosome and its genes are missing. Researchers have divided the deletion type of chromosomal aberration into the following four types:

• Terminal deletion.

• Intercalary deletion.

• Homozygous deletion.

• Heterozygous deletion.

In terminal deletion, the segment of chromosomes or genes is missing from the terminal part with a single break. In intercalary deletion, chromosomes or genes are missing from between, and in such a kind of deletion error, two breaks in the segment can be identified. Homozygous deletion describes the loss of chromosome segments or genes from the homologous chromosome pair, and heterozygous deletion represents the loss of chromosomal segments or genes from any homologous chromosome pair. Loss of genetic material and loss of genes are associated with deleterious effects and abnormal signs and symptoms.This error is expressed with a range of signs and symptoms specific to every genetic disorder.

How Is 9-p Deletion Caused?

9-p deletion disorder is caused by the deletion of genetic material on chromosome 9 in the distal part of the short arm. In most cases, the deletion of genetic material is noted at the terminal end of chromosome 9. More significant deletions show more complex features than smaller 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 each cell in the entire body of an individual. Chromosomes 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. The deletion of the genetic material generally occurs due to a spontaneous error and is mostly not inherited.

What Are the Clinical Features of the 9p Deletion Genetic Disorder?

The following are the most commonly reported general clinical features:

• Growth retardation.

• Speech disability.

• Motor skills retardation including daily activities like sitting and standing are affected, which causes difficulty in carrying out daily activities.

• Attention deficit hyperactivity disorder is a commonly noted feature in 11q 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; children suffering from this disorder 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 9-p deletion:

• Trigonocephaly is a unique feature noted in infants with 9-p deletion. The forehead of these individuals has a triangular shaped or keel shape. This is due to the altered fusion of brain sutures.

• 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.

Is 9p Deletion Disorder Inherited?

9p deletion is a genetic error and is not genetically inherited. This occurs due to a random error during the reproductive cell's production of eggs and sperm) or during early fetal development. Affected people have no history of a similar disorder in the past, but they may pass this chromosomal deletion on to their children. Five to ten percent of individuals even inherit these chromosomal deletion errors from parents unaffected by 9-p deletion disorder. These chromosomal abnormalities produce symptoms that are typical of this genetic error.

What Are the Management Protocols for 9-p Deletion Disorder?

A definite treatment protocol is still being researched. 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. Dental practitioners aim to improve individuals' oral hygiene so that the caries rate is reduced. Specialized doctors treat individuals with severe signs and symptoms, including heart and kidney disorders, with the utmost care.

Conclusion:

9-p deletion disorder is a rare genetic disorder caused by the deletion of genetic material in chromosome 9's short arm p. The signs and symptoms are different in every individual; thus, clinicians should thoroughly examine the patients. Concrete treatment plans and protocols are unavailable, but various research projects are going on in medical genetics to treat this disorder. Genetic mapping and targeted gene therapy are extensively studied for their applications in diagnosing and treating rare genetic disorders like the 9-p deletion.