Overview of Inheritance Patterns

Cure Rare Disease is currently developing 15+ therapeutics to treat rare genetic neuromuscular diseases. Keep reading for an overview of the different inheritance patterns of the diseases that CRD is working on.

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Basic Background of Inheritance

Most cells in the human body contain 46 chromosomes, made up of 22 pairs of autosomal chromosomes, and 2 sex chromosomes. For any given pair of chromosomes, a child inherits one from each parent because each of the parent's gametes, or sex cells, only contain 23 chromosomes. Genetic inheritance can become very complex, with concepts such as independent assortment, gene linkage, and more, but for the purposes of this blog, we will not be focusing on those ideas. It is also important to note that other diseases might be caused by multiple mutated genes and may have more complicated inheritance patterns than the ones listed below. 

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X-linked Recessive Inheritance

Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) both have an X-linked inheritance pattern, as the dystrophin gene is located on the X chromosome. DMD and BMD are also recessive, meaning that all of the X chromosomes in the cell must carry the mutated gene. Therefore, a person with two X chromosomes must have the mutated gene on both chromosomes, while a person with an X and a Y chromosome would only need to have a mutation on the one X chromosome to inherit the disease. This is why males are predominantly affected by DMD and BMD.

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Autosomal Recessive Inheritance

Limb girdle muscular dystrophy types 2b, 2g, and 2i and ADSSL1 gene-related myopathy have autosomal recessive inheritance patterns. In order to have an autosomal recessive disease, a person must inherit 2 copies of the mutated gene; if they only have 1, they are called a carrier and do not experience symptoms. There is a 25% likelihood of 2 carrier parents having a child with the disease, as shown in the figure below. 

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Autosomal Dominant Inheritance

Spinocerebellar Ataxia Type 3 has an autosomal dominant inheritance pattern. This means that for a person to have the disease, only 1 of the 2 copies of the gene must carry the mutation. A person cannot be a carrier for an autosomal dominant condition, unlike the recessive diseases mentioned previously.