chromosomal anomalies

Definition: Chromosomal diseases are caused by chomosomal anomalies .

A chromosome abnormality, disorder, anomaly, aberration, or mutation is a missing, extra, or irregular portion of chromosomal DNA. It can be from an atypical number of chromosomes or a structural abnormality in one or more chromosomes.

Chromosome mutation was formerly used in a strict sense to mean a change in a chromosomal segment, involving more than one gene.

Chromosome anomalies usually occur when there is an error in cell division following meiosis or mitosis. There are many types of chromosome anomalies. They can be organized into two basic groups, numerical and structural anomalies.

The term "karyotype" refers to the full set of chromosomes from an individual; this can be compared to a "normal" karyotype for the species via genetic testing. A chromosome anomaly may be detected or confirmed in this manner.

Consequences

It is estimated that 50% of spontaneous abortuses during the early months of gestation have a demonstrable chromosomal abnormality; there are, in addition, numerous smaller detectable errors and many others still beyond our range of identification. About 1% of all newborn infants possess a gross chromosomal abnormality.

Chromosomal anomalies

 numerical chromosomal anomalies

• ploidy anomalies (aneuploidy )
  • triploidy
  • tetraploidy

• autosomal monosomies

• autosomal trisomies
  • trisomy 21 (Down syndrome )
  • trisomy 13
  • trisomy 18
  • trisomy 8
  • trisomy 9

• autosomal tetrasomies

 structural chromosomal anomalies

• deletions
  • chromsome 13 deletion
  • 18q- syndrome (del18q)
  • 18p- syndrome (del18p)
  • 4p- syndrome (del4p) (Wolf-Hischhorn syndrome )
  • 5p- syndrome (del5p) (cat-cry syndrome )
  • 11p- syndrome (del11p)
  • 17p- syndrome (Miller-Dieker syndrome )
  • isodicentric 22 (22pter-q11) (Schmid-Fraccaro syndrome )
  • 21q- syndrome (del21q)
  • 22q- syndrome (del22q)

 chromosomal duplications

 chromosomal recombinaisons

• recombinant chromsome 8 syndrome (RC8S )

 chromosomal translocations

 ring chromosomes

 gonosomal anomalies

• monosomy X (45,X) (Turner syndrome )
• 47,XXY
• 47,XXX
• 47,XYY

 mosaicism

See also

 anomalies
 chromosomes