Intellectual Developmental Disorder, X-Linked, Syndromic, Siderius Type (MRXSSD)

What is Intellectual Developmental Disorder, X-Linked, Syndromic, Siderius Type (MRXSSD)?

It is a rare genetic syndrome that affects only males. It presents mainly with intellectual disability.

X-linked mental retardation occurs in around 1 in every 5-6,000 males. However, the Siderius type is much rarer and its exact prevalence is currently unknown. It is believed to affect less than a handful of individuals.

This syndrome is also known as:
Mental Retardation, X-linked, Syndromic, Siderius Type; Siderius X-linked mental retardation syndrome; Siderius-Hamel Syndrome

What gene changes cause Intellectual Developmental Disorder, X-Linked, Syndromic, Siderius Type (MRXSSD)?

It is caused by mutations in the PHF8 gene.

The syndrome is inherited in an X-linked recessive pattern. This makes it much more common in males. Females are the carriers of the mutated gene.

What are the main symptoms of Intellectual Developmental Disorder, X-Linked, Syndromic, Siderius Type (MRXSSD)?

The main symptoms of the syndrome include intellectual disability and developmental delay. This is usually identified as mild to moderate. This delay includes delayed motor development and delayed speech development.

A cleft lip and palate are also common symptoms of the syndrome. Affected individuals also usually have unique facial features that include a long face, sloping forehead, broad nasal bridge, low-set ears, and large hands.

Possible clinical traits/features:
Scoliosis, Synophrys, Abnormality of the nose, Cleft palate, Non-midline cleft lip, Preaxial hand polydactyly, Large hands, Intellectual disability, Low posterior hairline, Long face, Cognitive impairment, Cryptorchidism.

How is it diagnosed?

To find out if someone has a diagnosis of intellectual Developmental Disorder, X-Linked Syndromic, Siderius Type (MRXSSD), it is important to have a consultation and evaluation with a clinical genetic specialist.  Specialists may also suggest specific genetic testing or other types of tests to help reach a diagnosis.  FDNA’s AI technology can help speed up the diagnostic process by analyzing facial features and other health information.

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