Choice B reason Huntington disease is caused by a mutation in the HTT gene that encodes for the huntingtin protein. The mutation involves an expansion of the CAG trinucleotide repeat in the gene, which results in an abnormal protein with an elongated polyglutamine tract. This protein gains a new toxic function that interferes with the normal function of other proteins and causes neuronal degeneration in the brain.

Choice A reason:

Loss-of-function mutation is a type of mutation that reduces or eliminates the normal function of a gene or protein. This can result in diseases such as cystic fibrosis, phenylketonuria, or sickle cell anemia.

Choice C reason:

Haploinsufficiency mutation is a type of mutation that reduces the amount or activity of a gene or protein to less than 50% of the normal level. This can result in diseases such as Marfan syndrome, familial hypercholesterolemia, or Waardenburg syndrome.

Choice D reason:

Dominant negative mutation is a type of mutation that produces an abnormal protein that interferes with the normal protein and prevents it from functioning properly. This can result in diseases such as osteogenesis imperfecta, Ehlers-Danlos syndrome, or Holt-Oram syndrome.

Choice D reason: GDM can increase the risk of congenital disorders in the fetus, such as neural tube defects, cardiac defects, and cleft lip and palate. GDM is a condition that occurs when the mother develops insulin resistance and hyperglycemia during pregnancy. This can affect the fetal development and cause various complications, such as macrosomia, hypoglycemia, polycythemia, or respiratory distress syndrome.

Choice A reason:

Neural tube defects are congenital disorders that occur when the neural tube fails to close properly during the first month of embryonic development. This can result in defects such as spina bifida, anencephaly, or encephalocele. GDM can increase the risk of neural tube defects by altering the maternal-fetal glucose metabolism and affecting the folate metabolism.

Choice B reason:

Cardiac defects are congenital disorders that occur when the heart or blood vessels fail to form or function properly during the fetal development. This can result in defects such as atrial septal defect, ventricular septal defect, patent ductus arteriosus, or tetralogy of Fallot. GDM can increase the risk of cardiac defects by causing fetal hyperinsulinemia and hypoxia, which can impair the cardiac morphogenesis and differentiation.

Choice C reason:

Cleft lip and palate are congenital disorders that occur when the upper lip or palate fail to fuse completely during the first trimester of fetal development. This can result in defects such as unilateral or bilateral cleft lip, cleft palate, or both. GDM can increase the risk of cleft lip and palate by affecting the maternal-fetal glucose metabolism and causing oxidative stress and inflammation in the developing tissues.

Choice A reason "Trisomy 21." Down syndrome is a chromosomal disorder that occurs when there is an extra copy of chromosome 21 in the cells. This can result in physical and mental developmental delays and various health problems. The features that the nurse observed are typical of Down syndrome, such as slanted eyes, a flat nose bridge, a protruding tongue, and a single palmar crease.

Choice B reason:

"Monosomy X." Turner syndrome is a chromosomal disorder that occurs when there is a missing or partially missing X chromosome in females. This can result in short stature, infertility, heart defects, and other health problems. The features that the nurse observed are not typical of Turner syndrome, which may include a webbed neck, a low hairline, a broad chest, or swollen hands and feet.

Choice C reason:

"XXY." Klinefelter syndrome is a chromosomal disorder that occurs when there is an extra X chromosome in males. This can result in low testosterone levels, infertility, gynecomastia, and other health problems. The features that the nurse observed are not typical of Klinefelter syndrome, which may include tall stature, small testes, sparse body hair, or learning difficulties.

Choice D reason:

"Deletion of 5p." Cri du chat syndrome is a chromosomal disorder that occurs when there is a deletion of part of the short arm of chromosome 5. This can result in intellectual disability, microcephaly, facial abnormalities, and other health problems. The features that the nurse observed are not typical of Cri du chat syndrome, which may include a high-pitched cat-like cry, epicanthal folds, low-set ears, or a small jaw.

Choice A reason:

Teratogenic factor. A teratogenic factor is an environmental factor that can cause congenital disorders by interfering with the normal development of the fetus during the prenatal period. Teratogenic factors can include drugs, chemicals, infections, radiation, or maternal conditions that can affect the fetal growth and differentiation. Some examples of teratogenic factors are alcohol, thalidomide, rubella, ionizing radiation, or diabetes mellitus.

Choice B reason:

Mutagenic factor is an environmental factor that can cause genetic disorders by inducing changes in the DNA sequence or structure of the cells. Mutagenic factors can include chemicals, radiation, or viruses that can damage the DNA and cause mutations or chromosomal aberrations. Some examples of mutagenic factors are benzene, ultraviolet light, or human papillomavirus.

Choice C reason:

Carcinogenic factor is an environmental factor that can cause cancer by promoting the abnormal and uncontrolled growth of cells. Carcinogenic factors can include chemicals, radiation, or viruses that can interact with the DNA and cause mutations or epigenetic alterations that affect the gene expression or function. Some examples of carcinogenic factors are tobacco smoke, asbestos, or hepatitis B virus.

Choice D reason:

Epigenetic factor is an environmental factor that can cause genetic or congenital disorders by modifying the gene expression or function without changing the DNA sequence or structure. Epigenetic factors can include chemicals, nutrients, hormones, or stress that can affect the DNA methylation, histone modification, or microRNA expression that regulate the gene activity or silencing. Some examples of epigenetic factors are folate, estrogen, or cortisol.