**Question:** Which of the following does not have a X-linked pattern of inheritance?

A. Hemophilia
B. Duchenne muscular dystrophy
C. Congenital cataract
D. Gaucher disease

**Core Concept:** X-linked inheritance is a mode of genetic transmission where the gene is located on the X chromosome. In females, both X chromosomes are active, while in males, only one X chromosome is active due to the process of X-inactivation. The inheritance pattern is influenced by the sex of the individual and the presence of a functional allele (allele with a normal gene) on the X chromosome.

**Why the Correct Answer is Right:** The correct answer, Congenital cataract, is not X-linked because it is a genetic disorder that affects the eye and does not involve the X chromosome. Instead, it is inherited in an autosomal pattern, meaning that it can affect both males and females equally. In an autosomal pattern, the inheritance depends on the number of chromosomes with the abnormal gene (one or both) in the parents and the offspring.

**Why Each Wrong Option is Incorrect:**

A. Hemophilia: Hemophilia is an X-linked recessive disorder affecting blood clotting factors. Males (XY) are more severely affected than females (XY or XX). Hemophilia B is associated with factor IX deficiency, while Hemophilia A is associated with factor VIII deficiency. Both disorders are inherited through the X chromosome, making hemophilia incorrect in this context.

B. Duchenne muscular dystrophy: Duchenne muscular dystrophy is an X-linked recessive disorder affecting muscle proteins. Males are severely affected, while females are usually carriers without symptoms. This option is also wrong as it involves the X chromosome.

C. Gaucher disease: Gaucher disease is an X-linked recessive disorder affecting lipid storage in cells. It affects both males and females, but the severity can vary based on the number of affected alleles in the individual. This option is incorrect as it involves the X chromosome.

**Clinical Pearl:** It is essential for medical students and practitioners to understand the difference between sex-linked and autosomal inheritance patterns. Sex-linked disorders generally affect both males and females, while autosomal disorders affect both sexes equally or with varying degrees based on the number of affected alleles. This distinction helps in predicting the sex of an affected individual, determining the severity of symptoms, and counseling parents about the chances of affected offspring.