-

Case #17
Subject: Embryology
Medcloud™
Case #17
Subject: Embryology
Medcloud™
Case #17
Subject: Embryology

• Balanced translocation - 21%

In balanced translocations, genetic material from nonhomologous chromosomes is exchanged without there being a change to the total amount of genetic material (e.g., balanced Robertsonian translocation). The offspring of individuals with a balanced translocation involving chromosome 21 (typically between chromosomes 14 and 21) are at increased risk for Down syndrome. However, individuals with balanced translocation have 45 chromosomes and no phenotypic alterations.
B. Meiotic nondisjunction - 22%
Approx. 95% of cases of Down syndrome occur through meiotic nondisjunction of chromosome 21, which results in three, instead of two copies of chromosome 21 (i.e., full trisomy 21). Nondisjunction can occur due to unequal separation of homologous chromosomes during meiosis I or sister chromatids during meiosis II. Individuals with Down syndrome due to meiotic nondisjunction would have the same clinical features, as seen in this patient, but a total number of 47 chromosomes instead of 46 chromosomes.
C. Mitotic nondisjunction - 6%
Mosaic trisomy accounts for approx. 1% of cases of Down syndrome and is caused by nondisjunction of chromosome 21 during mitosis. In individuals with trisomy 21 due to mosaicism, two different cell lines are present, the trisomy 21 cell line (47 chromosomes) and the normal cell line (46 chromosomes). However, this patient's karyotype shows 46 chromosomes in all tested cells.
E. Uniparental disomy - 4%
Uniparental disomy arises when an offspring inherits a set of homologous chromosomes from only one parent. Individuals with uniparental disomy have 46 chromosomes but are commonly asymptomatic, as opposed to this patient. Some cases of uniparental disomy are associated with disorders of imprinting, such as Angelman syndrome and Prader-Willi syndrome, but not Down syndrome.

Medcloud™
Case #18
Subject: Embryology
A 1-day-old boy is in the neonatal intensive care unit due to congenital anomalies noted at birth. The infant was born vaginally at 36 weeks gestation to a 25-year-old woman, gravida 2 para 2, who declined prenatal testing and reported decreased fetal movement in the week preceding delivery. The infant was not latching well for the first 24 hours but has urinated and stooled. Examination shows a small face and jaw with a prominence on the back of the head. The oral mucosa is pink, but the hands and feet are mildly cyanotic. There are no skin creases on the palmar aspect of the digits. There is overlapping of the fingers bilaterally along with convexity of bilateral soles and limited hip abduction. A murmur at the left lower sternal border is heard on auscultation. Which of the following cardiovascular abnormalities is most likely present in this patient?