Human genetic

The human body is composed of billions of cells in which DNA is found. It is composed of 23 000 genes. The DNA is distributed on 46 chromosomes, of which 23 are inherited from the father and 23 are inherited from the mother. Every gene is then present in two copies. The image below represents a picture of the human chromosomes contained in a cell. This analysis is called a karyotype.

Credit : BY Servier Medical Art

The first 22 pairs of chromosomes are numbered from 1-22 and are similar in men and women. The last pair is composed of sex chromosomes which determine an individual gender. A man will have one X and one Y (like the picture above) while a woman will have two X chromosomes.

Chromosomal rearrangements (CNV)

The chromosomal rearrangements, also called CNV (copy number variation), are variations in the number of copies of certain portions of chromosome. A deletion means that a chromosomal part is present in only one copy. On the contrary, a duplication means that a chromosomal part is present in three copies. Some CNVs have an impact on the neuro-development.

Disease-associated CNVs

  • The 600-kilobase (kb) break points 4 and 5 (BP4-BP5) 16p11.2 deletion and duplications (chr16; 29.6-30.2 megabase) are among the most frequent genetic causes of autism spectrum disorder (ASD), schizophrenia, and other neurodevelopmental disorders.

    D'Angelo, D. (2016)
  • Previous studies have demonstrated that ASD is diagnosed in approximately 18% of deletion carriers and that this CNV affects global cognition by shifting the IQ approximately 2 SDs without altering the variance.

    D'Angelo, D. (2016)
  • Regarding cognitive domains, language impairment in deletion carriers was reported in several case series, and specific assessments showed below-average performance in comprehension, expression, and reading skills with a 71% rate of speech and language disorder.

    Hippolyte, L. (2015)

Glossary

Copy number variant - CNV

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