More than 2000 hereditary (genetic) diseases have been documented and 0,7% of newborns have an unbalanced chromosomal anomaly. Miscarriages or sterility in couples can also be related to a genetic defect. Overall 4% of live births show an anomaly that may or may not be due to a genetic defect.
II-Motives for seeking genetic advice
II-1. Couple before reproduction
II-2. Couple at risk
III- Genetic counseling consultation
III-1. Climate of anxiety
The family tree must be complete and include the deceased individuals, the pregnancy losses, and the causes of death.
III-3. Diagnosis of the disease
IV- The counseling will be based on:
V- Risk evaluation
V-1. Autosomal dominant inheritance
V-2. Autosomal recessive inheritance
V-3. X-linked recessive inheritance in the family
V-4. Multifactorial inheritance
V-5. Chromosomal diseases
Most often due to a parental meiotic non disjunction: low risk of recurrence but not null ( 1 to 2 % of cases of a standard trisomy 21).
Occasionally due to an abnormal segregation secondary to a parental rearrangement: the risk of recurrence is not easily established (due to the type of the rearrangement, the size and the nature of the segment involved, the sex of the carrier).
Increases the risk of occurrence of an autosomal, recessive or multifactorial disease.
Measure the consanguinity coefficient. Notable risk in the case of a known familial disease.
V-7. Exposure to mutagens
Low risk but a prenatal diagnosis can be offered to reassure the couple if one of them has undergone anticancerous treatment during the months preceding the pregnancy
A prenatal evaluation must be proposed , if feasible, in future pregnancies, for any of the above situations.
VI- Adult onset of hereditary diseases
The treatment of hereditary metabolic diseases during childhood and the transfer of those pediatric patients after the adolescence have contributed to the development of adult genetic medicine. Late onset disorders like Huntington disease and several others diagnosed at a later age are now often cared for by those clinics.
VII- Speciality clinics
VII-1. Speciality clinics
. Adequate genetic counseling is more than often offered in speciality clinics particularly for blood dyscrasias, mucoviscidosis, renal diseases, hearing deficits and more frequently now in breast, ovaries and colon cancer clinics.
. Individuals seeking genetic counseling may be guided towards one of those clinics .
VII-2. Role of genetic units
VIII- Associations, parents groups
Individuals suffering from a chromosomal or monogenic disease are often invited to join an association. The muscular dystrophy and mucoviscidosis associations were among the first to be known to the public. For instance short stature individuals will gain by sharing their views on how to improve their daily activities such as access to public services and also be able to contact organizations or para-medical clinics that may diminish the burden of their handicap.
VIII-2. Parents groups
Parents of individuals affected with a genetic disease will share, during those informal meetings, information that may not have been given to them during the counseling sessions: for instance details on nurseries, stimulation groups, nursing homes, specialized schools, summer camps and on the expected course of development and the handicaps specific to the diseases.
IX- Corollaries to genetic counseling
The genetic counseling must also offer to individuals and families information and advice on the treatment of genetic diseases that is by offering a follow up or else by directing them towards para-medical services like dietetics, speech therapy , physiotherapy or others who can help those patients.
IX-2. Contact with patients
Genetic counseling implies the transmission and interpretation of data.
The geneticist will guide the individual and family members and support them in their actions if they face a risk of transmitting or developing a genetic disease. The genetic counseling is not limited to a session of information and it is appropriate to plan a visit to make sure that the information has been understood correctly, to update the medical history and quite often to inform individuals of the recent findings in diagnostic facilities and treatment.
IX-3. Contact with families
The diagnosis and counseling must be complemented by the follow up of families. It is frequent in genetic clinics to insure the follow up of several members of the same family particularly in familial chromosomal aberrations, monogenic dominant or X-linked diseases like for instance hemophilia .
IX-4. Patients charts and registries
Nominal information confidentiality must be applied according to local rules. Consent forms specific to clinical interventions are part of the dossier. We recommend to patients to inform the genetics clinic of their new residence especially if a follow up is indicated.
IX-5. Disclosure of results
It is frequent during the course of familial investigations that one or more individuals will accept to undergo a diagnostic test but refuse to be informed of the results. This situation is frequent in the susceptibility tests or during the screening for degenerative diseases for which there is no treatment. All information referring to the risk of reproduction must be given to the individuals concerned.
X- Screening programs.
All screening tests for a genetic disease to identify affected individuals or normal carriers must include an informed consent and foresee appropriate genetic counseling. A newborn screening program for the detection of a metabolic disease will include a follow up if the screening test is abnormal or a control is requested.
X-2. Children and adults
A systematic screening program may be justified when there is a high incidence of hereditary diseases for instance blood dyscrasias in Mediterranean countries or Tay Sachs disease among Ashkenasic Jews.
A screening program must be complemented by the publication of information in the interest of the population under study and offer an individual and confidential approach if results are positive.
|Written||2002-09||Louis Dallaire, Jean-Loup Huret|
|Centre de Recherche, Hôpital Ste-Justine, Montréal, Canada (LD); Genetics, Dept Medical Information, UMR 8125 CNRS, University of Poitiers, CHU Poitiers Hospital, F-86021 Poitiers France (JLH)|
|© Atlas of Genetics and Cytogenetics in Oncology and Haematology||indexed on : Tue Jan 17 17:43:51 CET 2017|
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