What are some possible genotypes for parents?

Geneticists use 2 by 2 tables, called Punnett Squares, to predict the possible genetic traits (or genotypes) for children. Below are two Punnett Squares depicting possible CLS inheritance.

Table 1: Affected father (X`Y), unaffected mother (XX).

	X`	Y
X	X`X	XY
X	X`X	XY

Male children in this scenario will not be affected. Female children will be affected by the dominant trait on the X chromosome.

Table 2: Affected mother, heterozygous (X`X), unaffected father (XY).

	X	Y
X`	X`X	X`Y
X	XX	XY

In this scenario, 50 percent of daughters and 50 percent of sons will be affected.

In short: If the mother is heterozygous (X`X) she will pass it on to about half (50 percent) of her children.
If the mother is homozygous (X`X`) she will pass it on to ALL of her children.
If the father is affected (X`Y) he will pass the trait on to his daughters, but not to his sons.

Depending on the severity of the disorder, however, many CLS patients do not have children. Instead, CLS is often the result of a new mutation on the X chromosome.

How is Coffin Lowry Syndrome (CLS) Inherited?

Coffin-Lowry Syndrome follows an X-linked inheritance pattern. Unlike many other X-linked disorders, CLS is dominant, not recessive.

X-linked inheritance is a pattern located on the X-Chromosome. Females have two X chromosomes, while males have an X and a Y chromosome. This means that when females inherit an X-linked recessive trait, the other X will “cover up” the mutated gene. In X-linked dominant, however, the mutated gene cannot be “covered up,” and is usually still displayed by females.

Since males have only one X chromosome, there is no other X to “cover” the mutation. Therefore, dominant and recessive X-linked traits will always show up in males. One important feature of X-linked diseases is that the father cannot pass it to his son, but can pass it to his daughter.

However, 70-80 percent of affected CLS patients have no family history of the disorder. In these cases, a new mutation has occurred on the X-chromosome by either insertion or deletion of base-pairs.

What is a Genetic Counselor?

Genetic counselors serve patients by helping them assess risks, teaching them about their specific disease, and providing supportive counseling for affected individuals and their families. They often refer individuals or families to local services that provide additional assistance. They have specialized graduate degrees in both medical genetics and counseling.