Question: How many people are affected by X-linked creatine deficiency ?
Answer: The prevalence of X-linked creatine deficiency is unknown. More than 150 affected individuals have been identified. The disorder has been estimated to account for between 1 and 2 percent of males with intellectual disability.
Source: GHR

Question: Is X-linked creatine deficiency inherited ?
Answer: This condition is inherited in an X-linked pattern. The gene associated with this condition is located on the X chromosome, which is one of the two sex chromosomes. In females (who have two X chromosomes), a mutation in one of the two copies of the gene in each cell may or may not cause the disorder. In males (who have only one X chromosome), a mutation in the only copy of the gene in each cell causes the disorder. A characteristic of X-linked inheritance is that fathers cannot pass X-linked traits to their sons. In most cases of X-linked inheritance, males experience more severe symptoms of the disorder than females. About half of females with one mutated copy of the SLC6A8 gene in each cell have intellectual disability, learning difficulties, or behavioral problems. Other females with one mutated copy of the SLC6A8 gene in each cell have no noticeable neurological problems.
Source: GHR