4th Chromosome

The 46 human chromosomes come in 23 pairs and constitute the human genome. The first 22 pairs are called autosomes and the 23rd pair is the sex chromosome. The 4th pair of chromosomes is one of the autosomes that determine somatic traits. Typically, the numbering is based on size, from largest to smallest.

The 4th chromosome has about 727 protein-coding genes and stretches approximately 190 million base pairs. Any change or imbalance in the 4th chromosome is termed as 4th chromosome abnormalities or aberrations.

Explore: Chromosomal Abnormalities in Humans

4th Chromosome Abnormalities

Chromosomes are distributed to each daughter cell during cell division in a very precise process which can sometimes be prone to error. The error or imbalance can be a loss (monosomy) or gain (trisomy) of a chromosome. Structural changes such as deletion, inversion, translocation and duplication also constitute abnormalities.

The following are some abnormalities associated with the 4th chromosome.

Achondroplasia

It is a genetic disorder caused due to the mutation of the FGFR-3 gene present on chromosome 4. This gene is responsible for the production of collagen and other structural proteins in bones and tissues. Thus, a spontaneous genetic mutation in this gene leads to short-limbed dwarfism. This disorder can also be inherited from parents.

Hypochondroplasia is also a similar termed disorder which is caused due to defects in the FGFR-3 gene. This also results in individuals with short stature.

Ellis-van Creveld Syndrome

This is also a genetic disorder (rare) caused due to defects in the EVC gene. The EVC gene is located on the short arm of chromosome 4 (4p16). Still, the function of a healthy EVC gene is not fully known. This syndrome is also characterised by short-limbed dwarfism, cleft palate, polydactylism, etc. It is a rare disorder that can typically be observed in isolated populations.

Wolf-Hirschhorn Syndrome

This disorder is due to the microdeletion of the short arm of the 4th chromosome. It is also called deletion 4p syndrome. In most cases, the deletion is new and in some cases, it is inherited from a parent with chromosomal translocation. This syndrome results in reduced intellectual ability, restricted growth and a characteristic craniofacial phenotype.

Central Hypoventilation Syndrome

It is a congenital breathing disorder that can also sometimes occur due to severe spinal or brain injury. PHOX2B is a protein encoded by the PHOX2B gene located on the 4th chromosome. This gene plays a vital role in neural development. Central hypoventilation syndrome is typically associated with ineffective breathing during sleep.

Other Diseases

The other diseases associated with the 4th chromosome are Huntington’s and Parkinson’s disease. There are many autosomal recessive and autosomal dominant genes associated with Parkinson’s disease. Thus Parkinson’s is related to both chromosome 4 as well as chromosome 6. Likewise, the HTT or Huntington gene is located on the short arm of the 4th chromosome. Any mutation or defect in the HTT gene leads to this degenerative neurological disorder (Huntington’s disorder).

Trisomy 4p is due to repetition on the short arm (p) of the 4th chromosome. The p-arm appears thrice instead of twice. This abnormality leads to defects in hands, legs and craniofacial malformations. It is typically characterised by severe mental retardation.

Also Check: MCQs on Mendelian Disorders in Humans

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