Family history

Family history

Table 1. Family history screening questionnaire

*Only first-degree and second-degree relatives need be considered in this screening questionnaire

Reproduced with permission from Emery JD, Reid G, Prevost AT, Ravine D, Walter FM. Development and validation of a family history screening questionnaire in Australian primary care. Ann Fam Med 2014;12(3):241–49.

Taken from a Guideline for preventative activities in general practice 

What do I need to know?

Family history is particularly useful for assessing the risk of autosomal dominant inheritance When a condition follows an autosomal dominant pattern of inheritance, the family tree will usually reveal multiple affected members in multiple generations on the same side of the family. Dominant conditions or traits are expressed when only a single gene variant is inherited. Wide variability in clinical expression is common in many autosomal dominant conditions, even within the same family. Early onset of conditions, such as cancer, can be indicative of autosomal dominant inheritance within a family. Not all dominant conditions show 100% penetrance (eg BRCA1 gene mutations). and multifactorial inheritance Multifactorial inheritance, also called complex inheritance, can be attributed to a combination of genetic (ie single or multiple genetic variants), environmental and lifestyle factors. The number of necessary factors, and the impact those factors have on the presence or severity of a condition, will vary for different conditions and individuals. Often, when there are multiple susceptibility genes involved, there is an additive effect on the outcome (e.g. when calculating polygenic risk scores). Early onset of conditions, such as cancer, cardiovascular disease or type 2 diabetes, may be indicative of multifactorial inheritance within a family. This type of inheritance does not follow a characteristic pedigree pattern, but may look like autosomal dominant inheritance with incomplete penetrance. . Conditions with an autosomal recessive inheritance Autosomal recessive conditions affect either sex, and often occur in the absence of any family history. Recessive conditions or traits appear when an individual inherits two copies of pathogenic variants in the same gene (one from each parent). Parents of a child with an autosomal recessive condition are usually asymptomatic carriers. The affected child has two copies of the particular gene change. The recurrence risk of autosomal recessive conditions is one in four for each pregnancy. Wide variability in clinical expression is common in many autosomal recessive conditions. Autosomal recessive conditions are more common when the parents are consanguineous. or X-linked recessive inheritance Since a male inherits only one X chromosome (from his mother), when he has a pathogenic variant in a gene on the X-chromosome, he will have that condition. Males are usually more often and more severely affected because of X-inactivation in females. Since a male only passes his Y chromosome to his sons, there is no male-to-male transmission of X-linked conditions. With each pregnancy, females who are carriers of a pathogenic variant in a gene on the X-chromosome have a one-in-two chance of passing on the variant to each child. Sons who inherit the variant will be affected and daughters who inherit the variation will be carriers like their mothers. Daughters of affected males can only inherit the pathogenic variant from their father and are known as ‘obligate carriers’. pattern will often occur in the absence of family history (eg cystic fibrosis [CF]).

General information to collect in a family history includes:

• age of patient
• age at diagnosis of conditions in the family
• ancestry and cultural background
• step-relationships and adoption (ie: family members not genetically related to the individual)
• children born to parents who are blood-related ( consanguinity Consanguinity describes a relationship between two people who are related to each other because of a common ancestor. Consanguineous relationships occur in all population groups, but occur more frequently in certain cultures. The most common form of consanguineous relationships is between first cousins. Individuals who are blood relatives share a greater proportion of their genes than unrelated people, thus, these individuals potentially share pathogenic variants Pathogenic variant and gene mutation for the same autosomal recessive condition. When individuals are first cousins and there is no family history of a specific condition, or of other consanguineous relationships in previous generations, the risk of them having a child with a medical condition is approximately 5–6%, compared with 3–4% in the general population. This risk is higher in couples where there is a multi-generational tradition of first-cousin marriages, rendering couples closer in genetic relationship. )
• known genetic conditions.

Update the patient’s family history, including births, deaths and new diagnoses opportunistically. 

Markers of possible genetically determined conditions in a family history include:

• birth defects, multiple stillbirths and multiple miscarriages – consider referral to genetics services
• developmental delay (DD) – consider referral and ordering a chromosome microarray (CMA) and fragile X syndrome <link to chapter>  (FXS) testing (DD and intellectual disability [ID], FXS, autism spectrum disorder  [ASD])
• neurodegenerative conditions, premature ischaemic heart disease, sudden death – consider referral to genetics services
• early onset of common cancers and/or unusual combinations of rare cancers – refer to eviQ for further information about familial cancer syndromes.

Pedigree

Drawing a pedigree can be helpful in identifying patterns of inheritance (Table 1).

Table 1. Common pedigree symbols

	Male	Female	Sex unknown
Individual
Affected individual*
Affected individual with more than one condition*
Carrier
Deceased individual
Stillbirth (SB)
Pregnancy (P)

*Use a key or legend to define the condition(s) denoted by the shading in the pedigree.

Record the date on which the pedigree is drawn and update it as new information becomes available.

At each step, ask about the health of the family member being discussed.

It may not always be possible to complete the pedigree because of complexities such as adoption, a lack of reliable information or family disruption. It is important to consider such issues in each family. Step-by-step instructions for drawing a pedigree is shown in Table 2.

Table 2. Step-by-step instructions for drawing a pedigree

Step 1	Draw the symbol for the family member being seen. Indicate this person with an arrow and enter any pertinent details (eg name, age)
Step 2	If the individual has a partner, draw a line directly across to a symbol for the partner
Step 3	Ask about the number of pregnancies pertaining to the couple. Draw a reverse ‘T’ from the relationship line and add the symbol for each child and pregnancy
Step 4	Add a line from each child or pregnancy to the reverse ‘T’
Step 5	Ask about brothers and sisters for each partner. Add the relevant symbols alongside the corresponding person
Step 6	Indicate the relationship between siblings by drawing a vertical line stemming from each symbol and joining them together with a horizontal line
Step 7	Add a vertical line from this sibship line and add parents
Step 8	Indicate deceased family members by drawing a line through the symbol
Step 9	Repeat steps 5–8 for each parent of the family member you are seeing to include the aunts, uncles and grandparents