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SYNCRIP/HNRNPQ-Related Neurodevelopmental Disorder 

The SYNCRIP gene is also called HNRNPQ. This is because the gene was identified by multiple groups who called it different things. The official gene name is SYNCRIP.

SYNCRIP/HNRNPQ-Related Neurodevelopmental Disorder is caused by damaging genetic changes (variants) in the SYNCRIP gene. 
 

Genetics

SYNCRIP/HNRNPQ-Related Neurodevelopmental Disorder follows an autosomal dominant inheritance pattern.

Most variants are loss-of-function and result in a nonfunctional protein product that leads to a decreased amount than necessary the of SYNCRIP/hnRNPQ protein that is needed for normal cellular function (haploinsufficiency).

 

Missense and insertion/deletion (indel) variants are rarer but have been reported more frequently with increased genomic testing. The mechanism of such variants is still unclear, but may include loss-of-function or gain-of-function. No significant differences have been observed across variant types.

 

To date, all variants reported in the medical literature are de novo, which means that they occurred for the first time in the affected person and were not inherited from a parent. However, we are aware of inherited variants that have yet to be published. These seem to be inherited from an affected parent, but their child may have differing/more severe clinical features.

Image by Sangharsh Lohakare

Developmental Delay/Intellectual Disability

All HNRNPC-RNDD individuals have developmental delay/intellectual disability to date. This ranges from mild to moderate. 

Motor

Most individuals with HNRNPC-RNDD have motor delay. One individual who has a large exon 1-3 deletion did not have gross motor delay, but other individuals had delayed walking, with first steps being up to 2.5 years old. All individuals have delays in fine motor skills.

Structural Brain Anomalies 

Most individuals with HNRNPC-RNDD have structural brain anomalies. These are quite variable. The following have been reported:

  • Abnormal ventricles, particulary large ventricles (ventriculomegaly)

  • Absent cochlea (leading to hearing loss)

  • Polymicrogyria

  • Delayed myelination

  • Cysts

  • Thalamic volume loss

  • Small sinuses

  •  

Muscles

Over half of individuals with HNRNPC-RNDD have hypotonia (low muscle tone).

A small number of individuals with variants that escape nonsense mediated decay have hypermobile joints.

Hand and Feet Differences 

About 60% of individuals with HNRNPC-RNDD have hand and/or feet differences. Reported differences include:

  • fetal fingertip pads or prominent fingertip pads

  • small metacarpals (bones of the hand)

  • sandal gap between toes

  • metatarsus adductus (front of the foot turns inward)

  • clinodactyly (curved finger)

  • brachydactyly (short fingers)

  • short or small hands or feet

Hearing Loss

Almost half of individuals with HNRNPC-RNDD have eye and/or vision anomalies. These include:

  • myopia (near-sightedness)

  • colobomatous microphthalmia

  • strabismus

Speech

All HNRNPC-RNDD individuals have speech delay or problems. Some individuals are nonverbal while some are delayed until 2-3 years old. Multiple people have articulation issues.

Behavioral Differences

Most individuals with HNRNPC-RNDD have behavioral differences. These include a happy demeanor, ADHD, autism spectrum disorder (ASD), and difficulty falling or staying asleep. Tics have also been reported.

Seizures

About a quarter of individuals with HNRNPC-RNDD have seizures. These have included:

  • absence seizures

  • generalized seizures

  • epilepsy

Individuals with variants that escape nonsense mediated decay are more likely to have seizures.

Skeletal Differences

About a third of individuals with HNRNPC-RNDD have skeletal differences. Individuals with variants that escape nonsense mediated decay are more likely to have skeletal differences. Reported differences include:

  • vertebrae anomalies

  • thin ribs

  • abnormal number of ribs

  • pectus excavatum-carinatum

  • tiba anomalies

  • open anterior fontanelle

  • short neck

  • brachycephaly

  • microcephaly

  • macrocephaly

Eye and Vision Anomalies

Almost half of individuals with HNRNPC-RNDD have eye and/or vision anomalies. These include:

  • myopia (near-sightedness)

  • colobomatous microphthalmia

  • strabismus

SYNCRIP/HNRNPQ Research

Here are the most up to date research papers on SYNCRIP/HNRNPQ-Related Neurodevelopmental Disorder

In this publication, Dr. Maddie Gillentine lead our team to further define the features of SYNCRIP/HNRNPQ-Related Neurodevelopmental Disorder. 

You can read the article here: 

Publications on HNRNPC

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Disclaimer: The information provided on this website is not intended to diagnose or treat a disease or disorder. Please direct any medical-related questions to your physician. The HNRNP Family Foundation is not responsible for any errors or omissions on this website.

The HNRNP Family Foundation is a 501(c)(3) EIN 92-2394844

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