Genetic Conditions Flashcards
Down syndrome
Chromosome21
FeaturesShort stature, simian crease, almond shaped eyes due to epicanthic folds, upslanting palpebral fissures, low set ears, brushfield spots, and poor muscle tone. Most have mild (IQ 50-70) to moderate (IQ 35-50) mental retardation
Angel man syndrome
Chromosome15q11 maternal origin
FeaturesFlapping hand movements (uplifted, flexed arms when walking), ataxia, pronounced verbal delay (compared to comprehension), serveve to profound learning disability, seizures and sleep problems
Prader willi
Chromosome15q11 paternal origin
FeaturesHyperphagia, excessive weight gain, short stature, frequent skin picking, mild learning disability, small gonads, and hypotonia
Cri du chat
Chromosome5p deletion
FeaturesCharacteristic cry like a meowing kitten, hypotonia, hypertelorism, a down-turned mouth, and microcephaly
ConditionVelocardiofacial syndrome (Di George syndrome)
Chromosome22q (deletion)
FeaturesCleft palate, cardiac problems, and learning disabilities. A higher rate of psychiatric disorders is also seen
ConditionEdwards’s syndrome (trisomy 18)
Chromosome18
FeaturesKidney malformations, upturned nose, webbing of second and third toes, and clubbed feet (rocker bottom)
ConditionLesch-Nyhan syndrome
ChromosomeXq26-27
FeaturesSelf mutilation, dystonia and writhing movements
ConditionSmith-Magenis syndrome
Chromosome17p11
FeaturesPronounced self injurious behaviour, self hugging, and a hoarse voice
Fragile x
ChromosomeX
FeaturesElongated face, large ears, large testicles, hand flapping, shyness, and little eye contact. It is an X-linked dominant disorder caused by the amplification of a CGG repeat in the 5 untranslated region of the fragile X mental retardation 1 gene (FMR1). These CGG repeats disrupt synthesis of the fragile X protein (FMRP) known to be essential for brain function and growth. The gene is located at Xq27. As with other trinucleotide repeat disorders (Huntington’s, myotonic dystrophy, Friedreich’s ataxia, and spinocerebellar ataxia) the greater number of repeats the more severe the condition.
The fragile X phenotype typically involves a variety of psychiatric symptoms, including features of autism, attention deficit/hyperactivity disorder, anxiety, and aggression.
Females as well as males are affected. This is through the process of X-inactivation, where one X in each female cell inactivates itself. Males are more severely affected because they have only one X chromosome.
It has a prevalence estimate of 1/3600-4000.
ConditionWolf Hirschhorn syndrome
Chromosome4p
FeaturesProfound mental retardation, microcephaly, seizures, down turned fishlike mouth, Greek warrior helmet face, and cleft lip
Patau syndrome
Chromosome13
FeaturesMental retardation, polydactyl, microcephaly, overlapping of fingers over thumb
Rett syndrome
ChromosomeXq28
FeaturesNormal for the first 12 months. Regression and loss of skills from around 18 months onwards. Hand-wringing movements are the most common feature. Associated learning disability is profound. Affects girls almost exclusively
Tuberous sclerosis
ChromosomeGenetically heterogeneous, linkage to 9q and 16p
FeaturesHamartomatous tumours affect various organs including the brain. 80% suffer with epilepsy. Autism, ADHD, and sleep problems are common
Williams syndrome
Chromosome7q11 deletion
FeaturesElfin like features, social disinhibition, and abnormal friendliness towards strangers. Very sensitive hearing is also seen. Advanced verbal skills, speech is articulate but superficial (referred to as cocktail party speech)
ConditionRubinstein-Taybi syndrome
ChromosomeUnclear, 16p deletions have been reported
FeaturesTend to be short with small heads. Associated with a friendly disposition and moderate learning disability
