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The Practical Guide to the Genetic Family History - Bennett L.R.

Bennett L.R. The Practical Guide to the Genetic Family History - Wiley-liss, 1999. - 265 p.
ISBN 0-471-22391-3
Download (direct link): thepracticalguidetot1999.pdf
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There are many unique issues in providing genetic counseling to individuals with mild mental retardation. The potential parent with learning disabilities may be less concerned about having a child “like me,” who also has learning delays, than having a child with physical birth defects (Finucane, 1998). These individuals may be unreliable family historians as well as concrete thinkers who may have difficulty conceptualizing the multitude of facts and figures that are traditionally reviewed in a typical genetic counseling visit. Finucane suggests that the content of such counseling should shift from “facts to feelings” (1998).
When a family history of mental retardation is identified, there are several key historical questions than can help with identification of syndromes and assist with
4.5 MENTAL RETARDATION 95
determining recurrence risks. These family history features are summarized in Table 4.12. A simple question to begin with is, “What diagnostic testing has been done?” Any child or person with unexplained mental retardation and dysmorphic features should have a chromosome study, particularly if there is a family history of mental retardation and miscarriages (suggesting a chromosome translocation). Individuals born before the 1970s may not have had a banded chromosome study. If an adult with features characteristic of a chromosomal syndrome had a normal chromosome study prior to the early 1990s, it is worth redoing the cytogenetic study using more sophisticated techniques. A normal chromosome study does not eliminate a genetic diagnosis. “Were any metabolic studies done?” (such as plasma amino acids, urine organic acids, lactate, or pyruvate). “Has any neurological testing been done?” (including brain imaging). Major brain malformations are more likely to have a genetic etiology than are minor structural abnormalities (Bundey, 1997).
“How severe is the learning disability? Do you have the results of any formal developmental testing?” About 30-40% of individuals with severe mental retardation have a single gene or chromosomal disorder, whereas mild mental retardation accounts for about 10% of such cases (Bundey, 1997). Severely aberrant mental development is usually clearly identified by 3 to 6 months of age. Documentation of actual IQ scores from affected family members is important. In the absence of medical records, descriptive information about the individual is useful. For example, “What life skills does the person have?” (e.g., feeding and dressing self, the ability to make change, living on own, driving a car or taking a bus, reading).
“Were the problems present from birth?” Developmental delays noted from birth or shortly thereafter suggest a teratogenic exposure in pregnancy, or a chromosomal problem. “Are the delays remaining static or progressing? If progressive, at what age did the changes begin?” Normal development, followed by a loss of developmental milestones or progressive decline in school performance, is suggestive of an inherited biochemical disorder (usually autosomal recessive or X-linked recessive; refer to Table 4.11) or a mitochondrial disorder. Persons with chromosomal aneu-ploidy usually do not regress in their development. Of course, other causes of developmental delay and failure to thrive that should not be overlooked include severe malnutrition, abuse, and neglect. Apparent regression may be attributed to environmental factors such as poorly controlled seizure activity, overmedication with anticonvulsants, intercurrent illness, emotional problems, or depression (Clarke, 1996).
“Were there problems in pregnancy or with birth? Was the child full term? Did the mother take any medications during pregnancy? Does the mother have any medical problems?” Answers to these questions can help determine whether the child’s delays are due to genetic or environmental causes (Robinson and Linden, 1993) such as the following:
• Maternal factors (e.g., maternal PKU, maternal myotonic muscular dystrophy)
• Teratogens (e.g., alcohol and/or recreational drugs, fetal hydantoin syndrome)
• Prematurity
96
DIRECTED MEDICAL-GENETIC FAMILY HISTORY QUERIES
TABLE 4.12 Features to Document In the Medical-Family History When a Family Member Has Mental Retardation.
• Severity of mental retardation (DSM IV-Classification)
Mild (IQ 50-55 to approximately 70)
Moderate (IQ 35-40 to 50-55)
Severe (IQ 20-25 to 35-40)
Profound (IQ < 20-25)
• The age the delays were noted
• Static or progressive mental impairment
• Intellectual abilities of parents of affected child
• Pregnancy and health history of affected child’s mother:
Full gestation or premature
Traumatic delivery or asphyxiation (e.g., cord accident)
Teratogenic exposure
Specifically ask about alcohol and recreational drugs Seizure medications
Maternal infections (syphilis, rubella, toxoplasmosis, cytomegalovirus, HIV, herpes simplex)
Maternal disease (e.g., PKU, myotonic dystrophy)
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