Genetic discoveries that will fundamentally change clinical practice are on the horizon for psychiatric illnesses. Like all physicians, psychiatrists need to prepare for these changes.

How have things changed already? In this issue, Hodgkinson and others examine genetic counselling for psychiatric illnesses in today’s molecular world. They review the basic principles of genetic counselling, then use schizophrenia as an example of current genetic counselling practice in this field. They also consider the future, when molecular testing may be available for some genetic forms of psychiatric illness.

Indeed, genetic counselling for psychiatric illness differs today from the practice as it was even a few years ago and has certainly changed since the last paper on this topic was published in The Canadian Journal of Psychiatry in 1984 (1). For example, Hodgkinson and others discuss a syndromic subtype of schizophrenia that must now be considered—22q deletion syndrome (22qDS), also known as velocardiofacial syndrome or DiGeorge syndrome. Up to 1 in 50 patients with schizophrenia, and up to 1 in 11 patients in subpopulations with childhood-onset schizophrenia or dual-diagnosis psychotic illnesses and mental retardation, may have this genetic syndrome (2). Genetic counsellors and clinicians must therefore have this syndrome in mind when they consider patients with schizophrenia, particularly those with accompanying learning difficulties, hypernasal speech, history of congenital anomalies, or any combination thereof (3,4). The specific recurrence risks and genetic counselling issues differ significantly for this subtype of schizophrenia, compared with the empiric risks for schizophrenia with which most psychiatric clinicians are familiar.

How much do clinicians treating patients with psychiatric illnesses today really need to know about genetics? What difference does it make if a patient has a genetic subtype of a psychiatric illness?

The first step for clinicians is consideration of, and possible referral of the patient for, genetic counselling. This may be more urgent for patients who have become pregnant or are considering a pregnancy, but it may also be important for family members. Clinicians therefore need to reconsider who among their patients should be referred for genetic counselling or an assessment by a medical genetics specialist, or both. Recent Canadian Clinical Practice Guidelines for the Treatment of Schizophrenia (4) recommend that all patients with schizophrenia be considered for genetic counselling with respect to family planning. Information about genetic counselling referrals should also be part of the standard education and support provided for family members of patients with schizophrenia. Relatives often have concerns about the risk for schizophrenia, particularly to offspring, but these concerns may be overshadowed by issues relating to immediate management of the individual with schizophrenia. Genetic counselling involves imparting the latest information about risks in a nonjudgmental way and often allays anxiety about risk. The alleviation of guilt in the parent of an individual diagnosed with a genetic syndrome such as 22qDS, who may have ascribed the behavioural manifestations to something done, or not done, during pregnancy, is not to be underestimated (5).

Diagnosis of a genetic form of psychiatric illness may also have important implications with respect to medical follow-up of a patient. The specific implications of genetic diagnosis for psychiatric treatments lie in the future. If, however, a seizure may be due to the hypocalcemia associated with a genetic subtype of illness (such as 22qDS) rather than to a psychotropic medication, it is clinically relevant for the treating psychiatrist today.

Demand for genetic counselling services is predicted to increase dramatically over the next decade (6), and psychiatric illnesses will be included in this. Molecular testing may become available for some forms of psychiatric illness. Psychiatrists treating patients with familial Alzheimer’s disease will already be familiar with this development: molecular testing is available for some forms of familial Alzheimer’s disease in which causal genes have been discovered (7). In this regard, Hodgkinson and others discuss counselling and ethical issues to do with the future availability of predictive testing in other psychiatric illnesses.

The other paper on genetics in this issue, by Bassett and others, provides insights into the genetics of schizophrenia and a window on the future of molecular genetics of psychiatric illness. Genetics, and in particular molecular genetic studies, pose challenges for clinicians and researchers alike with respect to interpretation. Bassett and others address these challenges. They present commonly held beliefs about the genetics of schizophrenia and explore current knowledge in this area. They also provide an informative table setting forth the most plausible locations for individual genes for schizophrenia as suggested by research findings to date. Both residents in psychiatry and psychiatrists in clinical practice may find the succinct explanations of the mechanisms for discordance in monozygotic (identical) twins, and of other phenomena related to genetics of schizophrenia and related disorders, helpful.

Although these papers focus on schizophrenia, the concepts may be extrapolated to any major psychiatric disorder. Molecular discoveries are around the corner. Already, mutations in a gene important in early development have been found to cause sporadic cases of Rett syndrome, a severe form of pervasive developmental disorder (8). The 2 papers presented in this issue of the Journal should assist clinicians to understand current issues in the genetics of psychiatric illness and may help clinicians prepare for the foreseeable genetic revolution in medicine (6).

References

1. Stancer H, Wagner D. Genetic counselling: its need in psychiatry and the directions it gives for future research. Can J Psychiatry 1984;29(4):289–94.
2. Bassett AS, Chow EWC, Weksberg R. Chromosomal abnormalities and schizophrenia. Am J Med Genet (Neuropsychiatr Genet) 2000;97:45–51.
3. Bassett AS, Chow EWC. 22q11 Deletion Syndrome: a genetic subtype of schizophrenia. Biol Psychiatry 1999;46:882–91.
4. Canadian Clinical Practice Guidelines for the Treatment of Schizophrenia. Can J Psychiatry 1998;43(Supplement 2):25S–42S.
5. Turk J, Hill P. Behavioural phenotypes in dysmorphic syndromes. Clin Dysmorphol 1995;4:105–15.
6. Collins FS. Shattuck lecture—Medical and societal consequences of the Human Genome Project. N Engl J Med 1999;341(1):28–37.
7. St George-Hyslop P. Molecular genetics of Alzheimer’s disease. Biol Psychiatry 2000;47:183–99.
8. Amir RE, Zoghbi HY. Rett syndrome: Methyl-CpG-binding protein 2 mutations and phenotype-genotype correlations. Am J Med Genet 2000;97:147–52.

Anne S Bassett, MD, FRCPC
Guest Editor