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INTRODUCTION

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Case 1: A 30-year-old G3P2 presents for her new OB visit at 10 weeks' gestation. She has had two full-term uncomplicated vaginal deliveries. Her second child, a boy now age 4, has recently been diagnosed with severe intellectual disability. Her family history is remarkable for a brother and two maternal uncles who have been diagnosed with “mental retardation.”

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A good family history is an important tool for making a diagnosis, and giving anticipatory guidance for many medical conditions, but is especially important for genetic conditions. The family history is essential for genetic counseling, including discussion of reproductive planning and understanding recurrence risks. Recording an accurate family history requires obtaining information on specific illnesses and medical conditions in family members, as well as pregnancy histories of female members. The importance of a family history is not to recognize a specific genetic disorder, but to uncover familial patterns of birth defects, cognitive disabilities, malignancies, or other medical problems. The information obtained may be important for early diagnosis, timely management and treatment, or reproductive planning. It should be updated at least annually, or sooner if new pertinent information is obtained.

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CONSTRUCTING A PEDIGREE

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Obtaining a family history can be time consuming, but the information obtained is invaluable for providing quality patient care.1 Although the use of checklists may be helpful in identifying areas of concern, it may miss key information that can be obtained by more direct questioning about the health of closely related family members. The most helpful method for recording a family history is the pedigree, which allows the identification of patterns that give clues to a potentially inherited disorder. Genetic counselors construct at least a three generation pedigree using standard symbols (Figure 4-1). Females are designated by circles, males by squares, and miscarriages or stillbirths of unknown gender by diamonds. Some geneticists use triangles or small filled circles to represent miscarriages. A deceased individual is designated with a diagonal line drawn through the symbol. Ages of death or gestational ages of the pregnancy loss should be written under the appropriate symbol. Symbols of individuals affected with a disorder should have their symbol shaded in, and the designation as to what the shading indicates should be given on a key on the pedigree. By convention the proband (patient) is denoted by an arrow. In denoting relationships, the male is placed on the left, and the female on the right, connected by a horizontal line. As noted in Figure 4-1, children are placed below the parents connected by a vertical line, and in the order of birth. Miscarriages and other pregnancy losses should be included in the appropriate birth order. Figure 4-2 shows a three generation pedigree for our case example with mental retardation that affects only males, and is inherited through unaffected females, strongly suggestive of an X-linked recessive form of mental retardation. The key features are ...

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