This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pediatrics
All of the following conditions have autosomal dominant inheritance except – 
Select and explain. 
A. Fabry's disease, B. Marfan's syndrome, C. Osteogenesis imperfecta, D. Ehlers Danlos syndrome
A: Fabry's disease
Answer: A: Fabry's disease 
Explanation: Autosomal dominant disorders 

Normally a gene pair has two alleles.
When one allele becomes abnormal due to mutation it is called heterozygous state.
When both the alleles become abnormal due to mutation it is called homozygous state.
Autosomal dominant disorders are manifested in heterozygous state, i.e. only if one allel is abnormal the disease will be manifested.

Autosomal dominant disorders