Germline mosaicism disorders are usually inherited in a pattern that suggests that the condition is dominant in either or both of the parents. That said, diverging from Mendelian gene inheritance patterns, a parent with a recessive allele can produce offspring expressing the phenotype as dominant through germline mosaicism. A situation may also arise in which the parents have milder phenotypic expression of a mutation yet produce offspring with more expressive phenotypic variance and a more frequent sibling recurrences of the mutation. Diseases caused by germline mosaicism can be difficult to diagnose as genetically-inherited because the
mutant alleles are not likely to be present in the somatic cells. Somatic cells are more commonly used for
genetic analysis because they are easier to obtain than gametes. If the disease is a result of pure germline mosaicism, then the disease causing mutant allele would never be present in the somatic cells. This is a source of uncertainty for
genetic counselling. An individual may still be a carrier for a certain disease even if the disease causing mutant allele is not present in the cells that were analyzed because the causative mutation could still exist in some of the individual's gametes. Germline mosaicism may contribute to the inheritance of many genetic conditions. Conditions that are inherited by means of germline mosaicism are often mistaken as being the result of
de novo mutations. Various diseases are now being re-examined for presence of mutant alleles in the germline of the parents in order to further our understanding of how they can be passed on. The frequency of germline mosaicism is not known due to the sporadic nature of the mutations causing it and the difficulty in obtaining the gametes that must be tested to diagnose it. == Diagnosis ==