Taking a family history
A very important tool in clinical genetics. One of the key skills in taking a family history is drawing a family tree with all relevant symbols (see Fig. 25.1). The approach described here is intended for routine use in a general paediatric setting. A more detailed approach is indicated when assessing a patient with a known or possible genetic disorder.
• Start with your patient. Draw a 4 symbol for a male; 5 symbol for a female.
• Next add symbols for your patient’s parents and siblings. Record basic information only, e.g. age, whether they are in good health, and whether there are any concerns regarding development. If an individual has died, note age and cause of death and annotate the family tree with an oblique stroke through the symbol.
• Ask whether there is any inherited disorder running in the family.
• Ask whether your patient’s parents are related (consanguinity increases the chance of an AR disorder). Consanguinity is indicated by drawing a double line on the family tree.
• Ask the key question ‘Has anybody else in your family had a similar problem to the patient?’ Be aware that some conditions have variable expression, e.g. del 22q11 may present with cleft palate in one member of the family and congenital heart disease in another.
• Extend the family tree upwards to include grandparents and sideways to include aunts, uncles, and cousins. If you have not revealed a familial problem by this stage, do not go further as you are unlikely to have missed an important familial disease with onset in childhood. In the case of a suspected X-linked disorder extend the family tree further on the maternal side (ask a clinical geneticist to help you with this).
• Shade those people in the family tree affected by the disorder. This will help determine whether there is a genetic problem, and, if there is, it will help to suggest the pattern of inheritance.
For an example of drawing a family tree see Fig. 25.2