Question:  Is Mitochondrial genetic disorders inherited ?
Answer: Are mitochondrial genetic disorders inherited? Mitochondrial genetic disorder can be inherited in a variety of manners depending on the type of condition and the location of the disease-causing change (mutation). Those caused by mutations in mitochondrial DNA are transmitted by maternal inheritance. Only egg cells (not sperm cells) contribute mitochondria to the next generation, so only females can pass on mitochondrial mutations to their children. Conditions resulting from mutations in mitochondrial DNA can appear in every generation of a family and can affect both males and females. In some cases, the condition results from a new (de novo) mutation in a mitochondrial gene and occurs in a person with no history of the condition in the family. Mitochondrial genetic disorders caused by mutations in nuclear DNA may follow an autosomal dominant, autosomal recessive, or X-linked pattern of inheritance. In autosomal dominant conditions, one mutated copy of the responsible gene in each cell is enough to cause signs or symptoms of the condition. In some cases, an affected person inherits the mutation from an affected parent. Other cases may result from new mutations in the gene. These cases occur in people with no history of the disorder in their family. A person with an autosomal dominant condition has a 50% chance with each pregnancy of passing along the altered gene to his or her child. When a condition is inherited in an autosomal recessive manner, a person must have a change in both copies of the responsible gene in each cell. The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition. When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier. A condition is considered X-linked if the mutated gene that causes the condition is located on the X chromosome, one of the two sex chromosomes (the Y chromosome is the other sex chromosome). Women have two X chromosomes and men have an X and a Y chromosome. X-linked conditions can be X-linked dominant or X-linked recessive. The inheritance is X-linked dominant if one copy of the altered gene in each cell is sufficient to cause the condition. Women with an X-linked dominant condition have a 50% chance of passing the condition on to a son or a daughter with each pregnancy. Men with an X-linked dominant condition will pass the condition on to all of their daughters and none of their sons. The inheritance is X-linked recessive if a gene on the X chromosome causes the condition in men with one gene mutation (they have only one X chromosome) and in females with two gene mutations (they have two X chromosomes). A woman with an X-linked condition will pass the mutation on to all of her sons and daughters. This means that all of her sons will have the condition and all of her daughters will be carriers. A man with an X-linked recessive condition will pass the mutation to all of his daughters (carriers) and none of his sons.