The CASK gene is found on the X Chromosome, and abnormalities to the gene can often cause developmental and motor delays. Microcephaly with pontine and cerebellar hypoplasia (MICPCH) often accompany a CASK mutation as well as autism traits. There are less than 100 cases known in the world, and more females than males are affected.
The severity of the delays depend on a couple things: the location of the abnormality (mutation, deletion, etc) on the gene, skewing, and mosaic patterns.
Genetics: a basic explaination
If the body were a book, chromosomes would be the chapters in the book. Genes would be the paragraphs, exons the sentences, and amino acids the words.
The CASK is a gene made of 27 exons, shown below in red. There are 920 amino acids, shown in blue. If there is an abnormality (deletion, mutation, etc), for example, on exon 22, amino acids between 650 and 675 may be missing or compromised, and everything following that amino acid is also compromised.
Back to the book analogy, if on the X-Chromosome (Chapter), exon 22 (paragraph), there is an abnormality in an amino acid (word), that amino acid no longer makes sense. Everything following that amino acid, also, does not make sense. The closer the abnormality is to the beginning of the gene (the closer it is to exon 1), the more severe the delays will be.
Females have two copies of their X-Chromosome. Typically in a healthy female, one X is inactivated, and the body sources from the other X-Chromosome. In some cases, both X’s are activated, but function at different ratios, for example 80:20 or 50:50.
In an 80:20 ratio, for a female affected by an abnormal CASK gene, the hope is that the 80 percent functioning X, is the chromosome with the healthy CASK gene. Although testing for a skew is possible (and expensive) there is currently no way to test which way the gene is skewed.
As males have only one X-Chromosome, skewing is not possible.
Not all cells carry a mutated CASK gene.
Mama Bear’s notes
At the end of the day, it doesn’t matter where your child’s mutation lies or if it’s skewed or in mosaic. Don’t let science, doctors, websites, lab results, tell you what your child can or cannot achieve. Our children are writing their own history. As parents we are here supporting, advocating, cheering and leading our children on, to their success.