Behavioral Phenotypes and Genetic Syndromes

  • Dimitrios Paschos
  • Nick Bass
  • André Strydom
Part of the Autism and Child Psychopathology Series book series (ACPS)


Over the past few decades genetic advances have resulted in increasing understanding of the etiology of intellectual disability (ID) syndromes while detailed phenotypic descriptions of behavior and mental disorders have become possible with validated and reliable assessment tools. Although the concept that certain ID syndromes are associated with a recognizable physical, behavioral, and cognitive “phenotype” is not new, it has gained considerable popularity among psychiatrists and psychologists working with this population. In this chapter, we will review the key aspects of behavioral phenotypes and genetic testing before describing some of the phenotypes associated with specific syndromes. For terms in italics, see “Glossary.”




Alternative version of a specific gene responsible for variations in characteristics such as blood type.

Copy number variations (CNVs): 

Abnormal number of copies of sections of the DNA on certain chromosomes. It is usually caused by submicroscopic structural rearrangements such as deletions, duplications, or translocations.

Comparative genomic hybridization (CGH): 

Method for analysis of CNVs in a part of DNA based on microarray technology.


Alleles that determine the phenotype seen in a heterozygote.

DNA methylation: 

Addition of a methyl group to DNA that may affect the expression of genes. An epigenetic mechanism.

DNA sequencing: 

Process of determining the order of nucleotides containing four bases [(G) guanine, (A) adenine, (T) thymine, and (C) cytosine] in a segment of DNA.


Any factor which influences the phenotype but is not part of the genotype.

FISH (fluorescence in situ hybridization): 

Technique developed in the early 1980s to detect the presence or absence of specific DNA sequences on chromosomes.

Genetic linkage map: 

A map of positions of known genes on the chromosomes.

Genomic imprinting: 

A natural process where certain genes are expressed or silenced (without alteration of their genetic code) depending on whether they are inherited from the mother or the father. Genetic conditions associated with imprinting defects include Angelman and Prader–Willi syndromes.

Genome-wide association studies: 

Examination of the genome for common variants in different individuals usually focusing on associations between SNPs and major diseases.


Photographed chromosomes arranged by size.


The tendency of genes close together on the same chromosome to be inherited together.

Linkage disequilibrium: 

The presence of certain combinations of alleles of closely linked genes on the same chromosome more often than it would be expected by chance.

Locus heterogeneity: 

This occurs when mutations in genes at different chromosomal loci cause the same phenotype.


Presence of two or more populations of cells with different genotypes in one organism. It results from a mutation during development affecting only a subset of the organism’s cells.

Polymerase chain reaction (PCR): 

Technique for copying strands of DNA in order to increase the available amount for study and analysis.


A gene that is masked in the presence of a dominant allele.

Sequence analysis (also called “gene sequencing” or “sequencing”): 

Lab technique by which the nucleotide sequence for a specific segment of DNA is determined.

Single-nucleotide polymorphisms (SNPs): 

A variant DNA sequence in which the base of a single nucleotide has been replaced by another (e.g., cytosine replaced by thymine).

Tumor suppressor gene: 

A gene that protects a cell from transforming to a cancerous cell. When this gene is mutated and loses or reduces its function, the cell can progress to cancer, usually in combination with other factors.

Uniparental disomy: 

Inheritance of both copies of a chromosome from one parent.

X-linked trait: 

Trait that is caused by mutation of a gene located on the X chromosome.

X-linked recessive disorder: 

A disorder due to a mutation in a gene on the X chromosome that causes the disease traits to be expressed in all males or females who are homozygous for the gene mutation.


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Copyright information

© Springer Science+Business Media New York 2014

Authors and Affiliations

  1. 1.Mental Health Sciences UnitCamden & Islington NHS Foundation Trust, University College LondonLondonUK

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