xlinkedrecessive

Leeds Fetal Medicine Unit Website

X-Linked recessive conditions

The mutant gene is carried on the X chromosome and the condition is usually only manifest in males. Healthy heterozygous females transmit the condition to 1 in 2 of their sons and 1 in 2 of their daughters become carriers. Affected males pass the mutant gene to all their daughters who become obligate carriers. In the majority of cases the male cannot pass on the mutant gene to his sons as he passes them his unaffected Y chromosome.

Females can occasionally exhibit X-linked conditions. This can occur in the woman is homozygous for the mutant allele. Women with a single X chromosome can manifest X-linked conditions and both haemophilia and Duchene muscular dystrophy have been described in women with Turner’s syndrome.

X-Linked Recessive Conditions

Becker muscular dystrophy

Duchene muscular dystrophy

Fabry’s disease

Fragile X syndrome

Haemophilias A and B

Hunters syndrome

Ocular albinism

Red-green colour blindness

Testicular feminisation syndrome

Wiskott-Aldrich syndrome.

X-Linked Recessive Family Tree

The disease is transmitted from healthy heterozygote female carriers to affected males and from affected males to all their daughters who become obligate carriers. Therefore any male grandchildren of the affected male would be at risk. This type of pedigree is said to show ‘diagonal’ or ‘knights move’ pattern of transmission.

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