False: Among people with LD, 85% have mild, 10% have moderate, 3–4% have severe and 1–2% have profound LD. Thus, there are 5 to 6 mildly learning disabled people for every person with a more severe degree of learning disability (Gelder et al 2006, p. 708).

False: Clinically recognizable birth injuries account for about 10% of LD (Gelder et al 2006, p. 717).

True: Also known as ‘Happy puppet syndrome’, Angelman syndrome is characterized by severe mental retardation, jerky limb movements, gait abnormalities, inappropriate bouts of laughter unrelated to prevailing affect or environment, epilepsy and a happy disposition (Gelder et al 2000, p. 1958; Johnstone et al 2004, p. 805).

True: Patients with autistic spectrum disorders may have a limited range of facial expression. They lack the ‘spontaneous seeking of shared enjoyment’, for example, showing and sharing. Their problems in emotional and social expression are paralleled by difficulties in recognizing and responding appropriately to the emotional expressions of others (Gelder et al 2000, p. 1725).

False: Both velocardiofacial syndrome and its more severe form the Di George syndrome are caused by a microdeletion on chromosome 22 (del (22) (q11.2q11.2)) (Johnstone et al 2004, p. 556).

True: In Down’s syndrome the frequency of seizures is 10%. Most have grand mal seizures (Fraser & Kerr 2003, p. 272).

False: Overall prevalence is higher, but the epidemiological profile is different. For example, Alzheimer’s dementia is more common while alcohol and drug misuse are less common (Fraser & Kerr 2003, p. 274).

False: The earlier descriptions of being very capable of mimicry, affectionate, music loving, easily amused, etc. were based on anecdotes and case reports. They have not been systematically validated (Craft et al 1985, p. 119; Gelder et al 2000, p. 1955).

True: Mitral valve prolapse, tricuspid valve prolapse and pulmonary valve fenestrations are the most common (Fraser & Kerr 2003, p. 268).

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: Cryptorchidism, i.e. undescended testes, is rare. Macro-orchidism, i.e. enlarged testes, is present in 90% of adults with Fragile X syndrome (Craft et al 1985, p. 122; Johnstone et al 2004, p. 551).

True: Hartnup disease is a rare inborn error of metabolism with nicotinic acid deficiency due to the reduced availability of its precursor tryptophan. Cases may be asymptomatic or present with a photosensitive skin rash, cerebellar ataxia and other neurological or psychiatric disturbances. Mental retardation occurs in some patients. A high protein diet can alter the deficient transport of neutral amino acids in most patients. In patients with symptomatic disease, daily diet supplementation with nicotinamide or nicotinic acid reduces the severity of symptoms (Lishman 1997, p. 573).

True: The overall prognosis is poor. However, survival into the 20s is common (Gelder et al 2000, p. 1959).

True: Klein–Levin syndrome usually occurs in male adolescents. They have periods of excessive sleepiness, overeating, hypersexuality and disturbed behaviour alternating with periods of normality. The frequency of episodes is once every 1–6 months and the duration is 1 day to a few weeks (Gelder et al 2000, p. 1803; Johnstone et al 2004, p. 782).

True: Attacks of hypertonia develop within a few weeks of birth followed by choreoathetosis, spasticity, ataxia and dystonia. Other features include severe mental retardation, microcephaly and epilepsy in about 50% (Gelder et al 2000, p. 1956; Mitchell 2004, p. 454).

True: Phenylketonuria occurs in 1 in 5000 to 20000 live births. It is an autosomal recessive condition caused by an error of amino acid metabolism. It is the most frequent and the most studied inborn error of metabolism (Fraser & Kerr 2003, p. 37; Gelder et al 2000, p. 1959; Johnstone et al 2004, p. 527).

True: Prader–Willi syndrome is a genetically heterogeneous disorder. About 70% of cases are caused by a deletion on chromosome 15 (q11q13) of paternal origin. It can also be caused by inheriting two chromosome 15s from the mother (maternal disomy) or by a paternal gene mutation (Gelder et al 2000, p. 1956; Johnstone et al 2004, p. 557).

True: Patients with Rett syndrome usually have severe or profound LD. This would correspond to an IQ score below 35 (Gelder et al 2000, p. 1955; Johnstone et al 2004, p. 553).

False: All patients with Patau’s syndrome (Trisomy 13) have severe LD, and most have microcephaly, congenital heart defects, marked hypertonia and myoclonic spasms. More than 50% die within the first month and only 5% survive beyond 3 years of age.

Edward syndrome (Trisomy 18) is associated with severe LD and epilepsy and often with congenital heart abnormalities. Only 10% survive beyond the first year (Craft et al 1985, p. 123; Johnstone et al 2004, p. 536).

True: Seizures occur in 60–80% of patients. Seizures of any type can occur. Infantile spasms are common in those with learning disability. Mild to severe LD is present in two-thirds (Gelder et al 2000, p. 1151; www.ninds.nih.gov).

False: Wilson’s disease or hepatolenticular degeneration is an autosomal recessive disorder of copper metabolism. The absence or dysfunction of the copper-transporting P-type ATPase coded on chromosome 13q14 results in deficiency of ceruloplasmin, impaired transport of copper from the liver to the biliary system and faulty excretion of copper. No abnormalities in copper absorption have been described (Craft et al 1985, p. 99; Gelder et al 2000, p. 1161; Mitchell 2004, p. 171).

True: Psychiatric morbidity is higher in those with LD than in the general population. The lower the IQ, the greater the problems and the more difficulty assessing and managing them (Gelder et al 2006, p. 709; Johnstone et al 2004, p. 563).

False: OCD is more common in LD. However, the diagnosis of OCD can be difficult because many patients may not have sufficient communication skills to reveal the presence of obsessive thoughts. Moreover, many patients with LD have repetitive and stereotyped behaviours that may be difficult to distinguish from OCD (Gelder et al 2000, p. 1968; Gelder et al 2006, p. 709).

False: Challenging behaviour occurs in 20% of children and adolescents and 15% of adults with LD (Gelder et al 2006, p. 709).

True: Naltrexone is an opioid antagonist. It has been used for rapid outpatient opiate detoxification in combination with clonidine; to aid relapse prevention in alcohol, opiate, cocaine and nicotine dependence; and in the treatment of eating disorders, obesity and pathological gambling. Naltrexone has also been used in the treatment of self-injurious behaviour in learning disability. The efficacy of naltrexone in most of these conditions remains unclear (Bouras 1999, p. 298; Fraser & Kerr 2003, p. 234; Sadock & Sadock 2005, p. 2877).