**Core Concept**
The child's symptoms of hemihypertrophy (asymmetric growth of limbs) and aniridia (absence of the iris) suggest a possible genetic disorder affecting multiple organ systems. This condition is likely to be associated with a mutation in a gene responsible for growth and development.

**Why the Correct Answer is Right**
The symptoms described in the question are characteristic of Beckwith-Wiedemann syndrome (BWS), a genetic disorder caused by overexpression of the IGF2 gene on chromosome 11p15.5. This overexpression leads to excessive growth and an increased risk of certain tumors. Aniridia is often seen in BWS due to the close proximity of the PAX6 gene to the IGF2 gene on chromosome 11. The PAX6 gene is responsible for eye development, and its disruption can result in aniridia. The absence of a family history suggests a new mutation in the IGF2 gene.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not match the clinical description of hemihypertrophy and aniridia. Turner syndrome (45,X) typically presents with short stature, gonadal dysgenesis, and other physical characteristics not mentioned in the question.

**Option B:** This option is incorrect because it does not account for the aniridia. Waardenburg syndrome (WS) is a genetic disorder characterized by sensorineural hearing loss, skin depigmentation, and other physical characteristics, but it is not typically associated with aniridia.

**Option C:** This option is incorrect because it does not match the clinical description of hemihypertrophy. Neurofibromatosis type 1 (NF1) is a genetic disorder characterized by neurofibromas, café-au-lait spots, and other physical characteristics, but it is not typically associated with hemihypertrophy.

**Option D:** This option is incorrect because it does not match the clinical description of aniridia. Fetal alcohol syndrome (FAS) is a condition caused by prenatal alcohol exposure, leading to growth retardation, facial abnormalities, and other physical characteristics, but it is not typically associated with aniridia.

**Clinical Pearl / High-Yield Fact**
Beckwith-Wiedemann syndrome is a genetic disorder that highlights the importance of genetic counseling and prenatal diagnosis. It also emphasizes the need for close monitoring for tumor development and other complications in affected individuals.

**Correct Answer:** B. Beckwith-Wiedemann syndrome.