chromosome 9 inversion

(inv(9))

One of the most common structural balanced chromosomal variations in chromosome 9 (specifically, pericentric inversions).

The sequence of genes in the inverted segment will be altered, that will cause problems in pairing during meiosis and may give rise to unbalanced rearrangements in the offspring including duplications and deletions of the inverted segment.
However, pericentric inversion of chromosome 9 does not cause unbalanced rearrangements.
The phenotypes depend on the breakpoint locations. For example, (p11q12) is believed to lead to no efect on the carrier nor causes any imbalances or miscarriages.

Inversions occur when there are two breaks within the same chromosome. The middle segment is inverted and re-fusion of the broken ends occurs.
(Types)
• pericentric inversion: Occurs around the centromere. The relative lengths of the sort and long arms may change.
• paracentric inversion: Not involve the centromere. It may occurs in either the long arm or the short arm. The lengths are not affected.

A pericentric ("around the center") inversion includes the centromere. After chromatid duplication in meiosis, the paired inverted chromosome forms a loop so that the loci pair with their homologous on the uninverted chromosome.
Occurence of a crossover event inside the loop produces 4 types of products in the gametes, that are 2 chromosomes with the standard and inverted gene order and 2 duplication / deletion products in which one or more loci have been duplicated or deleted.
Unlike a paracentric inversion, all gene loci are represented in the final products, and only the order of loci is changed.

(Symptoms)
• congenital anomalies
• growth retardation
• infertility
• recurrent pregnancy loss: It might be a hereditary anomaly caused by inv(9)(p22q13).
• complete hydatidiform mole: Might be caused by 46,XX,inv(9)(p11-q13).
• cancer
• Walker-Warburg syndrome: Autosomal recessive congenital muscular dystrophy associated with brain and eye abnormalities.
• optic nerve hypoplasia, bilateral
• hypogonadotropic hypogonadism

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