From OMIM
Xia-Gibbs syndrome (XIGIS) is characterized by impaired intellectual development with absent or poor expressive language, obstructive sleep apnea, mild dysmorphic features, and brain abnormalities (Xia et al., 2014). Patients with XIGIS can have a broad clinical spectrum with multisystemic involvement in addition to neurologic manifestation (Ritter et al., 2018).  http://www.omim.org/entry/615829

From MedlinePlus Genetics
Xia-Gibbs syndrome is a neurological disorder characterized by weak muscle tone (hypotonia), mild to severe intellectual disability and delayed development. Expressive language skills (vocabulary and the production of speech) are particularly affected; children with this condition usually do not speak their first word, a milestone typically achieved within the first year, until age two or later, and some never learn to talk. Development of motor skills, such as crawling and walking, can also be delayed.

Other signs and symptoms of Xia-Gibbs syndrome vary among affected individuals. Additional neurological features include poor coordination and balance (ataxia) and seizures. Feeding problems and sleep abnormalities can also occur in people with the condition, and many affected individuals experience short pauses in breathing while they sleep (obstructive sleep apnea). In some people with Xia-Gibbs syndrome, imaging tests of the brain show abnormalities in the brain's structure. For example, the tissue connecting the left and right halves of the brain (the corpus callosum) can be abnormally thin.

Xia-Gibbs syndrome can also affect physical development. Growth is usually impaired, and many affected individuals are shorter than their peers. Side-to-side curvature of the spine (scoliosis) is also a common feature. Some people with Xia-Gibbs syndrome have unusual facial features, such as a broad forehead, low-set ears or ears that stick out, widely spaced eyes (hypertelorism), eye openings that slant up or down (upslanting palpebral fissures or downslanting palpebral fissures), a flat bridge of the nose, or a thin upper lip. Other, less-common abnormalities involving the bones and skin include premature fusion of certain skull bones (craniosynostosis), unusually loose (lax) joints, and loose skin.

Neurodevelopmental disorders can also occur in Xia-Gibbs syndrome. Some affected individuals have autism spectrum disorder, which is characterized by impaired communication and social interactions, or attention-deficit/hyperactivity disorder (ADHD). Other problems can include aggression, anxiety, poor impulse control, and self-injury.  https://medlineplus.gov/genetics/condition/xia-gibbs-syndrome