Mental Retardation, X-Linked 99, Syndromic, Female-Restricted

Background and History: 

This condition is restricted to females and involves disorders of multiple organ systems as well as dysmorphic external features.

Clinical Correlations: 

The clinical features are highly variable and no one individual has all the features.  However, it is characteristic for newborns to have difficulties breathing and they feed poorly.  The skull appears short and the forehead is prominent.  The bridge of the nose is depressed, the upper lips are thin and the ears are low-set and rotated posteriorly.  There may be extra digits.  Abnormal hip development has been seen and scoliosis may be present.

Cataracts and strabismus (malalignment of the eyes) are often present.  The opening between the eyelids (the lid fissures) is narrow.

Internal abnormalities include heart defects and poor kidney development.  Brain imaging often shows abnormal development of brain structures.  Thyroid hormone disorders and frequent respiratory infections have been reported in some individuals.  Breast development is subnormal.


This is a female-restricted condition which results from a change (mutation) in a gene located on one of the X-chromosomes.  Since females have two X-chromosomes, they have a 50% chance of transmitting the mutation containing chromosome to each of their children.  Males who receive the anomalous X-chromosome are usually not viable so this disorder generally is seen only in females.  In reality females with this condition rarely reproduce so most cases occur without a family history of it.

Diagnosis and Prognosis: 

This is a rare disorder.  The facial and skeletal features at birth might be recognized as consistent with this condition but most of the features are found in other disorders as well.  Pediatricians and neurologists are likely to collaborate on the diagnosis and care.  An ophthalmologist should do a thorough eye examination. 

Additional Information
X-linked dominant, mother affected