when are hereditary defects present in a developing fetus
Birth defect Genetic disorders or diseases are all congenital, though they may not be expressed or recognized until later in life. Genetic diseases may be divided into single-gene defects, multiple-gene disorders, or chromosomal defects. Single-gene defects may arise from abnormalities of both copies of an autosomal gene (a recessive disorder) or of only one of the two copies (a dominant disorder). Some conditions result from deletions or abnormalities of a few genes located contiguously on a chromosome. Chromosomal disorders involve the loss or duplication of larger portions of a chromosome (or an entire chromosome) containing hundreds of genes. Large chromosomal abnormalities always produce effects on many different body parts and organ systems.
Huntington's disease HD is typically inherited from a person's parents, although up to 10% of cases are due to a new mutation.[1] The disease is caused by an autosomal dominant mutation in either of an individual's two copies of a gene called Huntingtin.[4] This means a child of an affected person typically has a 50% chance of inheriting the disease.[4] The Huntingtin gene provides the genetic information for a protein that is also called "huntingtin".[1] Expansion of CAG (cytosine-adenine-guanine) triplet repeats in the gene coding for the Huntingtin protein results in an abnormal protein, which gradually damages cells in the brain, through mechanisms that are not fully understood.[4] Diagnosis is by genetic testing, which can be carried out at any time, regardless of whether or not symptoms are present.[5] This fact raises several ethical debates: the age at which an individual is considered mature enough to choose testing; whether parents have the right to have their children tested; and managing confidentiality and disclosure of test results.[2]