True: The approximate prevalence of LD in the general population is:

True: Mild LD is over-represented in families from Social classes IV and V and has been associated with larger sibships, room overcrowding, lower income and lower maternal education (Johnstone et al 2004, p. 530).

True: Children with LD and an autistic spectrum disorder are likely to remain mute if they are using few words before age 6. They may be able to use single words appropriately if they are using words before their 13th birthday. It they use words by 6 and phrases by 12 then they may develop phrase speech (Fraser & Kerr 2003, p. 139).

True: Prosody is the stress, intonation and tone of voice. In Asperger syndrome, expressive and receptive aspects of communication are deficient. They have difficulty in understanding emotional aspects of communication that are communicated through prosody. They are unable to appreciate situational constraints and conventions of discourse and hence often violate them (Fraser & Kerr 2003, p. 147; Harris 2000, p. 226).

False: In Asperger syndrome, there is no clinically significant general delay in spoken or receptive language. Abnormalities of speech are more subtle. Prosody (the musicality of speech) is impaired and their speech is over-precise. They may also be insensitive to the social norms surrounding conversation (Fraser & Kerr 2003, p. 147; Gelder et al 2000, p. 1729).

False: The disorder leading to translocation is often inherited. The risk of occurence in a subsequent child is about 10%. In the case of a trisomy 21, the risk of occurence in a subsequent child is about 1% (Gelder et al 2000, p. 1955; Gelder et al 2006, p. 718).

True: Down’s syndrome is the most common cause of mental retardation. It affects approximately 1 in 1000 live births. Most people with Down’s have an IQ between 20 and 55 (moderate to severe learning disability). Only 15% have an IQ above 50 (Gelder et al 2000, p. 1954).

False: Vascular dementia is rare in Down’s syndrome. Down’s syndrome is considered an ‘atheroma free’ model. Lower blood pressure, low pulse rate and other protective factors may contribute to the reduced rates of vascular dementia. There may also be less exposure to environmental contributions such as smoking (Fraser & Kerr 2003, p. 268).

False: The mean blood pressure is 115/75 mmHg. Moreover, environmental contributions such as smoking are also lower (Fraser & Kerr 2003, p. 268).

False: All developments slow down after the first 6 months to 1 year. Language is not an exception to this (Gelder et al 2006, p. 717).

True: The Fragile X mental retardation 1 (FMR-1) gene responsible for Fragile X syndrome is caused by an abnormal nucleotide CGG repeat at a fragile site on the long arm of the X chromosome (Xq27.3) (Gelder et al 2000, p. 1953).

False: The prevalence rates are 1:4000–4500 in men and 1:8000–9000 in women (Johnstone et al 2004, p. 548).

False: Hunter’s syndrome is an X-linked mucopolysaccharide disorder. There are two forms. Type A presents with progressive LD and severe physical disabilities leading to death between 10 and 20 years of age. Type B is a milder form characterized by near normal intelligence and survival into their 60s or 70s. Type B Hunter syndrome is much harder to identify, and might only be recognized when looking at the maternal relatives of a child with Hunter syndrome (Gelder et al 2000, p. 1959; Harris 2000, p. 358).

True: Klinefelter syndrome (47XXY) occurs in 1:500 to 1:1000 men. 50% of all 47XXY conceptions are lost prenatally. One in 300 spontaneous abortions may be due to 47XXY (Johnstone et al 2004, p. 547).

True: It is a sex-linked disorder that almost exclusively affects boys. It is caused by a deletion of chromosome 26. It is associated with severe learning disability, chorea, athetosis and severe self-injurious behaviour. They have hypoxanthine phosphoribosyltransferase (HPRT) deficiency resulting in defective purine metabolism (Gelder et al 2000, p. 1956; Johnstone et al 2004, p. 807; Mitchell 2004, p. 454).

False: Metachromatic leucodystrophy is an autosomal recessive disorder of neural lipid metabolism resulting in the accumulation of galactosyl sulphatide in the affected tissue. There are three forms. The infantile form starts before the age of 3 years and progresses to severe motor and mental retardation. The juvenile form is less common and presents with motor and mental dysfunction. The adult form is the rarest and may present with dementia or psychotic disorder. Metachromatic leucodystrophy and epilepsy are the only two organic brain syndromes that have a higher than chance co-occurrence with schizophrenia (Gelder et al 2000, p. 1592; Lishman 1997, p. 758).

False: Phenylketonuria is an autosomal recessive disorder. Both parents have to transmit the abnormal gene in order for a child to have the disorder. Siblings of affected probands have a 1 in 4 (25%) risk.

False: Williams syndrome has the characteristic ‘elfin’ face, i.e. broad forehead, medial eyebrow flare, depressed nasal bridge, stellate pattern in the iris, widely spaced teeth, prominent lips, full prominent cheeks, wide mouth, short turned-up nose, long philtrum and flat nasal bridge (Harris 2000, p. 320; Johnstone et al 2004, p. 554).

True: Degree of retardation is variable. Only 50% may be retarded (Craft et al 1985, p.125).

True: About 60% of tuberous sclerosis complex is due to new mutations leading to dysfunction of hamartin and tuberin (Gelder et al 2000, p. 1958).

False: In general the overall intelligence is normal in Turner’s syndrome. There is a ‘Turner neurocognitive phenotype’ with normal verbal ability but visuomotor and visuospatial difficulties (Fraser & Kerr 2003, p. 89).

False: Williams syndrome is caused by a microdeletion of one elastin allele on the long arm of chromosome 7 (7q11.23) (Gelder et al 2000, p. 1957; Johnstone et al 2004, p. 555).

True: People with LD have limited communication skills and limited ability to express their subjective feelings. They are less likely than normals to complain of low mood. Depression in people with LD may manifest with irritability, unexplained temper tantrums or aggression, which are considered ‘depressive equivalents’ (Gelder et al 2006, p. 710; Johnstone et al 2004, p. 566).

False: The prevalence of schizophrenia in people with mild and moderate LD is 3% compared to 0.4% in the general population. Schizophrenia has an earlier onset, more poverty of thinking and less elaborate delusions and hallucinations in people with LD compared to the general population.

Kraepelin named dementia praecox arising in people with pre-existing intellectual impairment as Propfschizophrenie (Fraser & Kerr 2003, p. 157; Gelder et al 2006, p. 709; Johnstone et al 2004, p. 563).

False: People with LD have reduced brain and other reserves. This would make them more vulnerable to all forms of stress including pharmacological. They are more likely to have side-effects and toxic effects from antipsychotic drugs. They are also more sensitive to the anticholinergic side-effects and have a high risk of delirium. However, patients with LD are less likely to report adverse effects (Fraser & Kerr 2003, p. 223).