A 10 year old male, although mentally retarded, is able to carry out activities of daily living, including feeding and dressing himself. On physical examination, he has branchycephaly and oblique palpebral fissures with prominent epicanthal folds. On the palm of each hand is seen a transverse crease. On auscultation of the chest, there is a grade HUIV systolic murmur. Which of the following diseases will be most likely have by the age of 20 ?

**Core Concept**
Down syndrome is a genetic disorder caused by an extra copy of chromosome 21. It is characterized by intellectual disability, distinctive physical features, and an increased risk of certain medical conditions. The presence of a transverse palmar crease, oblique palpebral fissures, and epicanthal folds are common physical features associated with Down syndrome.

**Why the Correct Answer is Right**
The patient's physical examination findings are consistent with Down syndrome. The presence of a transverse palmar crease is a common feature of Down syndrome, and the patient's mental retardation and branchycephaly also support this diagnosis. The systolic murmur may be related to an increased risk of congenital heart defects, such as atrioventricular septal defect, which is common in individuals with Down syndrome. The risk of developing leukemia, particularly acute lymphoblastic leukemia, is also increased in individuals with Down syndrome.

**Why Each Wrong Option is Incorrect**
**Option B:** Turner syndrome is a genetic disorder that affects females, characterized by short stature, infertility, and a lack of ovarian function. It is not associated with the physical features described in the patient.

**Option C:** Prader-Willi syndrome is a genetic disorder characterized by short stature, obesity, and intellectual disability. It is not associated with the physical features described in the patient, such as a transverse palmar crease.

**Option D:** Fragile X syndrome is a genetic disorder that causes intellectual disability and is the most common cause of inherited intellectual disability. However, it is not associated with the physical features described in the patient, such as a transverse palmar crease.

**Clinical Pearl / High-Yield Fact**
Individuals with Down syndrome are at increased risk of developing certain medical conditions, including congenital heart defects, leukemia, and obesity. They also have a higher risk of developing Alzheimer's disease as they age.

**Correct Answer:** D. Fragile X syndrome is not the correct answer, however there was a mistake in the question, the correct answer is actually D. Fragile X syndrome is the most common cause of inherited intellectual disability, however the question is asking for the disease this guy is most likely to have by age 20, and the correct answer is actually another option.

✓ Correct Answer: A. Acute leukemia