X-linked intellectual disability, Siderius type

Alternate names

MRXSSD; Intellectual deficit X-linked Siderius type; Siderius Hamel syndrome

Definition

X-linked intellectual disability, Siderius type is characterised by mild to borderline intellectual deficit associated with cleft lip/palate. Preaxial polydactyly, large hands and cryptorchidism are sometimes present.

Epidemiology

The syndrome has been described in seven boys from two families.

Cause

• X-linked intellectual disability, Siderius type is caused by mutations in the PHF8 gene.
• This gene provides instructions for making a protein that is found in the nucleus of cells, particularly in brain cells before and just after birth.

Inheritance

X-linked recessive inheritance

• This condition is inherited in an X-linked recessive pattern.

Signs and symptoms

• This condition is characterized by mild to moderate intellectual disability that affects only males.
• Affected boys often have delayed development of motor skills such as walking, and their speech may be delayed.
• Individuals with X-linked intellectual disability, Siderius type frequently also have an opening in the lip (cleft lip) with an opening in the roof of the mouth (cleft palate).
• A cleft can occur on one or both sides of the upper lip.
• Some boys and men with this condition have distinctive facial features, including a long face, a sloping forehead, a broad nasal bridge, a prominent bone in the lower forehead (supraorbital ridge), and outside corners of the eyes that point upward (upslanting palpebral fissures).
• Affected individuals may also have low-set ears and large hands.

NIH genetic and rare disease info

• NIH info on X-linked intellectual disability, Siderius type

X-linked intellectual disability, Siderius type is a rare disease.