Cystinuria is an inherited condition (i.e. you were born with it). People with cystinuria usually inherit from parents who don’t have it. The way that it is inherited is through an autosomal recessive pattern – this means that you would need to have two of the cystinuira genes (one from each parent) to be affected by it. That is why usually your parents did not have the disease as they were only carriers. In the diagram below the ‘A’ represents a normal gene and ‘a’ represents a cystinuric gene. As one parent gives one gene each to their child, there is a 1 in 4 chance of receiving both ‘a’ genes.
This pattern of inheritance also explains why your brother or sister has a 1 in 4 chance of of having the disease, and a 1 in 2 chance of being a carrier.
One of the most common questions we are asked is whether you can pass cystinuria onto your children. As both parents have to give a cystinuria gene to your child then if you were to have a child with somebody who has cystinuria, then your child will also have cystinuria. If you were to have a child with somebody who is a carrier for cystinuria (just one cystinuria gene), then there is a 50% chance that your child will have cystinuria. It is important to note that carriers of the gene are usually asymptomatic and would not know that they are carriers. If you have a child with somebody who does not have a cystinuria gene, then none of your children will be affected, but they will all be carriers of the cystinuria gene.
If you have cystinuria then it is a good idea if your brothers and sisters are also tested, especially if they have ever had a stone.