Cohen syndrome is characterized by failure to thrive in infancy and childhood; truncal obesity in the teen years; early-onset hypotonia and developmental delays; microcephaly developing during the first year of life; moderate to profound psychomotor retardation; progressive retinochoroidal dystrophy and high myopia; neutropenia in many with recurrent infections and aphthous ulcers in some; a cheerful disposition; joint hypermobility; and characteristic facial features.

Marshall syndrome (MRSHS) is characterized by midfacial hypoplasia, cleft palate, ocular anomalies including high myopia and cataracts, sensorineural hearing loss, short stature with spondyloepiphyseal dysplasia, and arthropathy. In contrast to Stickler syndrome type II, it has less severe eye findings but striking ocular hypertelorism, more pronounced maxillary hypoplasia, and ectodermal abnormalities (summary by Shanske et al., 1997 and Ala-Kokko and Shanske, 2009).

Autosomal recessive form of oculodentodigital dysplasia.

Cerebellofaciodental syndrome is an autosomal recessive neurodevelopmental disorder characterized by delayed development, intellectual disability, abnormal facial and dental findings, and cerebellar hypoplasia (summary by Borck et al., 2015).

Developmental and epileptic encephalopathy-66 (DEE66) is a neurologic disorder characterized by the onset of various types of seizures in the first days or weeks of life. Most seizures have focal origins; secondary generalization is common. Seizure control is difficult at first, but may become easier with time. Affected individuals show global developmental delay with hypotonia, behavioral abnormalities, and dysmorphic features or ophthalmologic defects. Brain imaging often shows cerebellar dysgenesis. A subset of patients have extraneurologic manifestations, including hematologic and distal limb abnormalities (summary by Olson et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Liang-Wang syndrome (LIWAS) is a polymalformation syndrome apparent from birth that shows large phenotypic variability and severity. However, all patients have some degree of neurologic dysfunction. The most severely affected individuals have severe global developmental delay with impaired intellectual development and poor or absent speech, marked craniofacial dysmorphism, and visceral and connective tissue abnormalities affecting the bones and vessels. The least severely affected individuals lack seizures, significant dysmorphism, and visceral involvement; they come to attention for neurologic signs and symptoms, including developmental delay with speech delay, strabismus, and/or ataxia. About half of patients have brain imaging anomalies, notably cerebral and cerebellar atrophy and thin corpus callosum, whereas the other half have normal brain imaging (summary by Liang et al., 2019).

Neurodevelopmental disorder with speech impairment and with or without seizures (NEDSIS) is a phenotypically heterogeneous neurologic disorder whose severity appears to depend on the functional effect of the CACNA1I mutation. Severely affected individuals present in infancy with profound global developmental delay, hypotonia, delayed or absent walking, absent speech, feeding difficulties, cortical visual impairment, and onset of hyperexcitability and seizures in the first months or years of life. They achieve little or no developmental progress and may be tube-fed. Mutations in these individuals occurred de novo. In contrast, a milder phenotype associated with an inherited mutation has been found in a family with mild to moderate cognitive impairment and mild speech delay, usually without seizures (El Ghaleb et al., 2021).