True: While moderate to severe learning disabilities are mainly due to chromosomal anomalies, severe genetic misendowments and brain damage, only a small proportion of cases of mild learning disabilities are caused by these factors. Assortative mating would also tend to exacerbate the tendency for low IQ to occur in subsequent generations (Craft et al 1985, p. 84).

True: Maternal smoking is a risk factor for low infant birthweight, which is a risk factor for LD. Maternal smoking may independently affect fetal neurological development (Johnstone et al 2004, p. 533).

True: Both epidemiological and clinical studies report a male: female ratio of 3.5–4:1 for children with autism. However, this ratio varies with the IQ level. Females with autism who have IQs in the normal range are 50 times less common than males. The male:female ratio for Asperger syndrome appears to be closer to 9:1 (Fraser & Kerr 2003, p. 119; Gelder et al 2000, p. 1730).

True: The prevalence of Tourette syndrome in children with autistic spectrum disorders is 4.3–6.5%. This is higher than in the general population. The prevalence of Tourette syndrome is 4 per 10 000 in male adolescents and as high as 49 per 10 000 in American schoolchildren with behaviour disturbances (Fraser & Kerr 2003, p. 125; Gelder et al 2000, p. 1149)

False: Trisomy 21 accounts for 94% of cases. The cause is unknown. The risk of recurrence is 1%.

Translocation accounts for 3–5%. Translocation is familial. It can be identified at birth and used for genetic counselling. The risk of recurrence is 10%.

Mosaicism is found in 1–3%. They may have normal intelligence (Fraser & Kerr 2003, p. 33; Gelder et al 2000, p. 1955; Gelder et al 2006, p. 718).

True: There are three peaks, i.e. early infancy, the third decade and with the development of Alzheimer’s over the age of 40 years. The prevalence of epilepsy in Down’s syndrome is 10% overall, 40% in those over 40 and 80% in those with Alzheimer’s disease.

False: The prevalence of childhood autism in the general population is 2–5 per 10 000. The estimates of the prevalence of autistic features in Down’s syndrome vs. in those with an equivalent degree of LD from other causes vary, e.g. 5% vs. 10%, 11% vs. 7%. The definition of autism and the exclusion of other disorders such as behavioural phenotypes, OCD and depression that account for autistic spectrum behaviours influence prevalence estimates. Though these factors make an exact estimate of the frequency of autistic features difficult it is true that such features are not rare in Down’s syndrome (Fraser & Kerr 2003, p. 280).

True: Most children with Down’s syndrome have unilateral or bilateral hearing impairment. The high prevalence of conduction deafness especially in children may be caused by glue ear. Otitis media affects many children with Down’s syndrome and may be exacerbated by the structural anomalies of the ear. The hearing impairment in children is compounded by the later onset of sensorineural deafness. Thus, there is a high prevalence of both conduction and sensorineural hearing loss in adults with Down’s syndrome (Fraser & Kerr 2003, p. 269; Johnstone et al 2004, p. 542).

True: The narrowed hypopharynx increases the risk of sleep apnoea. Immune system defects increase the vulnerability to infections, particularly recurrent respiratory infections. Infection, especially pneumonia, is still the leading cause of death in Down’s syndrome (Gelder et al 2000, p. 1955; Johnstone et al 2004, p. 541).

False: Fragile X syndrome is caused by abnormal nucleotide CGG repeats at a fragile site on the long arm of the X chromosome (Xq27.3). In Fragile X syndrome, CGG repeats range from 230 to over 1000 while normal individuals have an average of 30 (6–54) (Gelder et al 2000, p. 1953).

False: Most female carriers have normal intelligence. However, 30–50% have mild LD (Craft et al 1985, p. 123; Gelder et al 2000, p. 1954).

True: Heller’s disease or childhood disintegrative disorder starts after normal development, usually for 2 years. Like autism, there is loss of cognitive and social skills. In addition, there is decline in motor skills and bowel and bladder control (Gelder et al 2006, p. 675).

False: The average IQ in Klinefelter syndrome (47XXY) is 90. Many have mild LD. Most have IQ above 60. Some have normal or above average intelligence (Johnstone et al 2004, p. 547; Sadock & Sadock 2002, p. 733).

True: Lennox–Gestaut syndrome typically starts between ages 1 and 8 years. 60% have evidence of pre-existing brain damage and LD. They have frequent, severe intractable tonic, atonic, myoclonic and atypical absence seizures. They have bilateral slow spike and wave complexes on the EEG (Gelder et al 2000, p. 1787; Lishman 1997, p. 242).

False: The overall prognosis of Lesch–Nyhan syndrome is poor. Most affected subjects die by early adulthood. Treatment is symptomatic. Gout can be treated with allopurinol. Kidney stones may be treated with lithotripsy. There is no standard treatment for the neurological symptoms. Carbidopa, levodopa, diazepam, phenobarbital or haloperidol may be used. There is no effective dietary treatment (Gelder et al 2000, p. 1956).

False: Phenylketonuria is an autosomal recessive condition caused by an error of amino acid metabolism (Fraser & Kerr 2003, p. 37; Gelder et al 2000, p. 1959; Johnstone et al 2004, p. 527).

True: Patients with Prader–Willi syndrome are described as pleasant and good tempered. However, they can manifest severe behavioural problems associated with hyperphagia and self-injurious behaviour in addition to temper tantrums (Gelder et al 2000, p. 1957).

False: Sturg–Weber syndrome (encephalotrigeminal angiomatosis) is a congenital, non-familial disorder of unknown incidence and cause. It occurs sporadically with no particular pattern of inheritance. Clinical features include a congenital facial birthmark (port wine stain), neurological abnormalities (brain angiomas and epilepsy), glaucoma and buphthalmos (Craft et al 1985, p. 110; http://www.sturge-weber.com; http://www.sturgeweber.org.uk).

False: TSC is due to spontaneous mutations (60%) or is inherited as an autosomal dominant disorder (40%). Two disease-determining genes have been identified: TSC1 and TSC2. TSC1 is on chromosome 9 (9q34) and encodes for the protein hamartin. TSC1 is less likely to cause mental retardation. TSC2 is on chromosome 16 (16p13.3) and encodes for the protein tuberin. About 60% of TSC is due to new mutations leading to dysfunction of hamartin and tuberin (Gelder et al 2000, p. 1958).

True: The first clue to diagnosis may be white patches on the skin, i.e. hypomelanotic macules. Skin lesions in TSC include facial angiofibroma, adenoma sebaceum, white ash leaf-shaped macules, shagreen patches, depigmented naevi, subcutaneous nodules and café au lait spots (Gelder et al 2000, p. 1958).

True: West syndrome consists of the triad of infantile spasms, severe LD and hypsarrythmia. Lennox–Gestaut syndrome usually starts between ages 1 and 8 years. They have severe intractable epilepsy and bilateral slow spike and wave complexes on the EEG.

Poor prognostic indicators in Lennox–Gestaut syndrome include onset before age 3 years, greater frequency of seizures and status seizures, onset after West syndrome and more slow wave and focal abnormalities on the EEG (Gelder et al 2000, p. 1787; Lishman 1997, p. 242).

True: Cognitive impairment increases with time. Fluctuating levels of consciousness with episodes of delirium occur. Delirium is more likely in the later stages and may be related to liver failure and seizures (Lishman 1997, p. 665; Mitchell 2004, p. 173).

False: People with LD may have limited communication skills and limited ability to express their subjective feelings. They are less likely than normal people to complain of low mood. Those with mild LD show similar symptoms to those with normal IQ, but with more loss of confidence and tearfulness. With lower IQ somatic symptoms such as changes in sleep, appetite, weight, energy and activity levels may indicate depression. Behavioural changes including psychomotor agitation, social withdrawal, increased self-harm, irritability, aggression, wandering and worsening of existing behavioural problems are also more common in those with LD and co-morbid depression (Bouras 1999, p. 179; Fraser & Kerr 2003, p. 159; Johnstone et al 2004, p. 566).

True: Personality disorders may be diagnosable, particularly in those with mild to moderate LD. Features such as dependence, passiveness and temperament may be features of LD, personality or both. A diagnosis of personality disorder may lead to exclusion from some services and, hence, many clinicians tend to withhold the diagnosis (Gelder et al 2006, p. 710; Johnstone et al 2004, p. 566).

True: Behavioural therapy, for example behaviour modification and operant conditioning techniques, is used effectively in a variety of difficult and disruptive behaviours in people with LD. Parents and teachers are taught to apply consistent rewards and consequences for adaptive and maladaptive behaviours. Behavioural therapy approaches based on detailed behaviour analysis of the antecedents and consequences of difficult behaviour are also effective.

Positive behavioural interventions are most effective for affective symptoms, e.g. depression and anxiety, and for social skills deficits.

Punishment procedures, e.g. extinction, disapproval, time-out, overcorrection are effective in destructive, aggressive and self-injurious behaviours.

Behavioural therapy has 65–75% success rate in stereotypic behaviours, psychophysiological symptoms and non-compliance. Behavioural therapy has 45–65% success rate in destructive behaviours. Inappropriate social interactions have only 35–45% success rate with behavioural therapy (Fraser & Kerr 2003, p. 103; Harris 2000, p. 520).