Genetics describes the study of the mechanisms that control inheritance. Genes are arranged linearly along long chains of DNA sequence called chromosomes. Chromosomes are responsible for the transfer of genetic information to offspring, and in doing so they also decide the sex of one’s offspring.
We each inherit an X chromosome from our mother and an X or Y chromosome from our father. If we inherit an X chromosome from our father we are female (XX), and if we inherit a Y chromosome from our father we are male (XY). This difference in X chromosome numbers leads to the unusual inheritance patterns of sex-linked disorders and is passed on by the mother.
Fabry disease is X-linked recessive which means that the mutated gene is located on the X-chromosome. This means that both males and females can have this gene (since both have at least one X chromosome) and is passed on by the mother, i.e. the female is referred to as the carrier.
It can be seen from Figure 2 that the son and daughter of an affected female have a 50% chance of receiving the mutated gene. An affected male will pass on the mutated gene to all of their daughters but none of their sons. In females (XX), the Fabry gene becomes recessive and the related phenotype (characteristics of Fabry) is suppressed. In males (XY), the Fabry gene becomes dominant and the related phenotype is displayed.
Figure 2: Genetic Inheritance, courtesy of Centre for Genetics Education
Figure 3 shows an example of a family tree and how Fabry Disease can be transferred through family generations. As the number of generations where occurrence of the condition is known or suspected, so the spread of the family tree increases.
Using the family tree is important in identifying suspected Fabry patients, especially as the disease can be somewhat difficult to detect based purely on symptoms. Genetic counselling is available to assist in this process of constructing a detailed inheritance pattern and the subsequent evaluation of all family members potentially at risk.
Figure 3: Example of a family tree