X - Linked dominant disorder - Rett syndrome, lissencephaly, hypophosphatemia

• X-linked inheritance, in which the defective gene is present on the female, or X-chromosome. X-linked inheritance may be dominant or recessive.

• X-linked dominant disorder may arise due to mutations in genes on the X chromosome.

• A single copy of the mutation is responsible for  causing the disease in both males and females.

• For the transmission of X linked dominant disorder, one copy of the allele is sufficient to cause the disorder when inherited from a parent who has the disorder

Example of X-linked dominant disorder

Rett syndrome

• It is a genetic disorder that is quite related to the nervous system and may affect  the brain.

• With this disorder, affected people may also lose their motor skills and speech. This disorder is mostly seen in females and rarely present in male.

• Initially the symptoms of this disorder  appear slowly but later on  affected persons feel difficulty in movement of muscle in hands and legs.

• It also disturbs coordination and communication. Rett syndrome ceases intellectual disability. Some activities like  rubbing and clapping etc. are also affected.

• The symptoms of this disorder are - Slowed growth, abnormal movement and coordination , irregular communication abilities, sleeping problem, Breathing problem, posture problem in spine etc.

• Rett syndrome is caused by the specific genetic mutation in the MECP2 gene.  This mutation affects the  production of protein needed for brain development.

• There is  no cure for Rett syndrome but some remarkable therapies are given to affected people to improve muscle movement and communication.

X - linked lissencephaly

• This disorder with abnormal genitalia  is a genetic condition in the development of the brain that is retarted and an impact is also seen in genital organs and pancreas also.It generally present in males.

• In this genetic disorder, the brain is developed without fold. Eventually the brain is smooth without the presence of a fold.

• These fold biologically termed as corpus callosum.  Brain abnormalities may cause various irregularities in the functioning of the brain.

• The symptoms of this disorder are intellectual  irregularities, retard developmental ,muscle stiffness weak muscle  and  trouble in feeding habit. 

• Abnormal genitalia  is also associated with this disorder like  small penis undescended testes. Sometimes  the external genitalia  is not clearly visible  male or  female .

• This genetic disorder is caused by the Mutations in the ARX gene that codes the ARX Protein. This protein is required   for the development of several organs like the brain, testes, and pancreas.  This protein is also involved in the  movement and communication in nerve cells. 

X linked hypophosphatemia

• It is caused by  the mutations in the PHEX gene .This gene encode a protein which is involved in regulating the amount of phosphate in the body.

• Mutations in this gene  raise the level of fibroblast growth factor 23. This factor regulates the reabsorption of phosphate in the kidneys.

• When the level of this growth factor is increased then it reduces  the reabsorption  of phosphate by the kidneys and causes hypophosphatemia.

• The symptoms of this disorder in  some people  have no any  bone related symptoms and  while  in others several symptoms appear like  Bone pain, Muscle pain and weakness, Joint pain caused tendons and ligaments., Abnormal tooth development.

• Tooth abscesses and dental Rickets  This genetic disorder is different from  common rickets because it cannot be treated by increasing vitamin D.