Genetic Determinants of Learning Disability Flashcards
Describe the IQ ranges associated with mild, moderate, severe and profound learning disabilities.
Mild: 50-70 Moderate: 35-50 Severe: 20-35 Profound: <20
Outline the 3 main types of cytogenetic abnormalities.
- Aneuploidy - e.g. trisomy 2. Translocations - reciprocal + Robertsonian 3. Deletions/duplications
Explain the difference between reciprocal and Robertsonian translocations.
Reciprocal - exchange of material between non-homologous chromosomes. Robertsonian - occurs in acrocentric chromosomes - break at centromere and long arms fuse together.
What is a 22q11 microdeletion and what does it cause?
22q11 microdeletion = DiGeorge syndrome, velocardiofacial:
- Cleft palate
- Congenital heart disease
- Hypocalcaemia
- Mild-moderate learning disabilities
- Renal abnormalities
90% de novo
Outline the pathophysiology of phenylketonuria.
- Lack of functional phenylalanine hydroxylase enzyme - cannot convert phenylalanine to tyrosine.
- Accumulation of Phe causes health problems such as developmental delay.
Describe the general characteristics of triplet repeat expansions and name 3 examples of conditions caused by this.
- Unstable/dynamic - can increase in size in next generation
- Instability depends on parent of origin
- General correlation between size of expansion and severity of disorder
- Huntington’s
- Fragile X syndrome
- Myotonic dystrophy
What is genomic imprinting and when do imprinted genes cause disease? Name 2 conditions that may be caused by imprinting.
- Disease is present even in the absence of apparent cytogenetic or molecular genetic abnormality.
- Epigenetic phenomenon - certain parts of the genome are “imprinted” - methylated.
- Genes are expressed in manner specific to parent of origin.
- Prader-Willi syndrome
- Angelman syndrome
What is a teratogen? Name 2 foetal syndromes caused by teratogens.
- Foetal alcohol syndrome
- Foetal valproate syndrome
Teratogen = substance which causes malformation of an embyro.
