7. Recessive HomozygousΒΆ

The next filter logic identifies Recessive Homozygous mutations. A recessive homozygous mutation occurs when there are two copies of the same recessive allele in the proband. This means that both parents are heterozygous for a recessive mutation and the proband is homozygous, carrying both copies. Similar to the Dominant Inherited, this filter logic integrates Genotype Zygosity. This can be visualized by expanding the Recessive Inheritance filter card, which filters for heterozygous variants in mother and father and homozygous variants in the proband.

Recessive homozygous interitance

Figure 7-1: Recessive homozygous inheritance.

The next filter logic, Gene Inheritance, is pulled from the ACMG Sample Classifier but is based on the gene inheritance from OMIM. The two options that are selected are Default (Recessive) and Recessive. Default (Recessive) is for a gene where the inheritance has not been identified as recessive or dominant, whereas the Recessive option is for a gene known to be recessive. You can also see that there are 32 variants that have a Gene Inheritance of Missing. These variants likely lack genotype zygosity, are reference alleles, or are not in a known gene. Together with the Auto Classification, there are 4 variants identified as Recessive Homozygous, which can be selected and viewed in the variant table and in Genome Browse.

Gene Inheritance

Figure 7-2: Gene Inheritance for Recessive Homozygous variants.

At this point, we will now take a look at Recessive Compound Heterozygous mutations.