Pitt-Hopkins-like syndrome-1 (PTHSL1) is an autosomal recessive neurodevelopmental disorder characterized by delayed psychomotor development, intellectual disability, severe speech impairment or regression, and behavioral abnormalities. Most patients have onset of seizures within the first years of life. Some patients may have cortical dysplasia on brain imaging (summary by Smogavec et al., 2016).

Complex cortical dysplasia with other brain malformations-13 (CDCBM13) is an autosomal dominant neurodevelopmental disorder characterized by global developmental delay with impaired intellectual development. Brain imaging shows variable neuronal migration defects resulting in cortical malformations, including pachygyria. More variable features include early-onset seizures and dysmorphic features. Some patients may also show signs of peripheral neuropathy, such as abnormal gait, hyporeflexia, and foot deformities (summary by Willemsen et al., 2012 and Poirier et al., 2013). For a discussion of genetic heterogeneity of CDCBM, see CDCBM1 (614039).

Familial focal epilepsy with variable foci (FFEVF) is an autosomal dominant form of epilepsy characterized by focal seizures arising from different cortical regions, including the temporal, frontal, parietal, and occipital lobes. Seizure types commonly include temporal lobe epilepsy (TLE), frontal lobe epilepsy (FLE), and nocturnal frontal lobe epilepsy (NFLE). A subset of patients have structural brain abnormalities, particularly focal cortical dysplasia (FCD). There is significant incomplete penetrance, with many unaffected mutation carriers within a family (summary by Ricos et al., 2016). For a discussion of genetic heterogeneity of FFEVF, see FFEVF1 (604364).

Familial focal epilepsy with variable foci (FFEVF) is an autosomal dominant form of epilepsy characterized by focal seizures arising from different cortical regions, including the temporal, frontal, parietal, and occipital lobes. Seizure types commonly include temporal lobe epilepsy (TLE), frontal lobe epilepsy (FLE), and nocturnal frontal lobe epilepsy (NFLE). A subset of patients have structural brain abnormalities, particularly focal cortical dysplasia (FCD). There is significant incomplete penetrance, with many unaffected mutation carriers within a family (summary by Ricos et al., 2016). For a discussion of genetic heterogeneity of FFEVF, see FFEVF1 (604364).

DEPDC5-related epilepsy encompasses a range of epilepsy syndromes, almost all of which are characterized by focal seizures, with seizure onset in a discrete area of the brain. While most individuals with DEPDC5-related epilepsy have a normal brain MRI, some have epilepsy associated with a cortical malformation, usually focal cortical dysplasia. Seizure syndromes include familial focal epilepsy with variable foci (FFEVF), autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE), familial mesial temporal lobe epilepsies (FMTLE), autosomal dominant epilepsy with auditory features (ADEAF), and infantile spasms. Although psychomotor development is usually normal, intellectual disability or autism spectrum disorder has been reported in some individuals.

The spectrum of COL4A1-related disorders includes: small-vessel brain disease of varying severity including porencephaly, variably associated with eye defects (retinal arterial tortuosity, Axenfeld-Rieger anomaly, cataract) and systemic findings (kidney involvement, muscle cramps, cerebral aneurysms, Raynaud phenomenon, cardiac arrhythmia, and hemolytic anemia). On imaging studies, small-vessel brain disease is manifest as diffuse periventricular leukoencephalopathy, lacunar infarcts, microhemorrhage, dilated perivascular spaces, and deep intracerebral hemorrhages. Clinically, small-vessel brain disease manifests as infantile hemiparesis, seizures, single or recurrent hemorrhagic stroke, ischemic stroke, and isolated migraine with aura. Porencephaly (fluid-filled cavities in the brain detected by CT or MRI) is typically manifest as infantile hemiparesis, seizures, and intellectual disability; however, on occasion it can be an incidental finding. HANAC (hereditary angiopathy with nephropathy, aneurysms, and muscle cramps) syndrome usually associates asymptomatic small-vessel brain disease, cerebral large vessel involvement (i.e., aneurysms), and systemic findings involving the kidney, muscle, and small vessels of the eye. Two additional phenotypes include isolated retinal artery tortuosity and nonsyndromic autosomal dominant congenital cataract.

Galloway-Mowat syndrome-8 (GAMOS8) is an autosomal recessive disorder characterized by impaired psychomotor development, poor overall growth with microcephaly, and early-onset progressive nephrotic syndrome associated with focal segmental glomerulosclerosis on renal biopsy. Some patients may have seizures, and some may die in childhood (summary by Fujita et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of GAMOS, see GAMOS1 (251300).

Mitochondrial complex IV deficiency nuclear type 2 (MC4DN2) is an autosomal recessive multisystem metabolic disorder characterized by the onset of symptoms at birth or in the first weeks or months of life. Affected individuals have severe hypotonia, often associated with feeding difficulties and respiratory insufficiency necessitating tube feeding and mechanical ventilation. The vast majority of patients develop hypertrophic cardiomyopathy in the first days or weeks of life, which usually leads to death in infancy or early childhood. Patients also show neurologic abnormalities, including developmental delay, nystagmus, fasciculations, dystonia, EEG changes, and brain imaging abnormalities compatible with a diagnosis of Leigh syndrome (see 256000). There may also be evidence of systemic involvement with hepatomegaly and myopathy, although neurogenic muscle atrophy is more common and may resemble spinal muscular atrophy type I (SMA1; 253300). Serum lactate is increased, and laboratory studies show decreased mitochondrial complex IV protein and activity levels in various tissues, including heart and skeletal muscle. Most patients die in infancy of cardiorespiratory failure (summary by Papadopoulou et al., 1999). For a discussion of genetic heterogeneity of mitochondrial complex IV (cytochrome c oxidase) deficiency, see 220110.

Congenital muscular dystrophies resulting from defective glycosylation of alpha-dystroglycan (DAG1; 128239) are characterized by early onset of muscle weakness, usually before ambulation is achieved; intellectual disability mild brain anomalies are variable (Balci et al., 2005; Godfrey et al., 2007). Congenital muscular dystrophy-dystroglycanopathies with or without impaired intellectual development (type B) represent the intermediate range of the spectrum of dystroglycanopathies. They are less severe than muscular dystrophy-dystroglycanopathy with brain and eye anomalies (type A; see MDDGA1, 236670), previously designated Walker-Warburg syndrome (WWS) or muscle-eye-brain disease (MEB), and more severe than limb-girdle muscular dystrophy-dystroglycanopathy (type C; see MDDGC1, 609308). Genetic Heterogeneity of Congenital Muscular Dystrophy-Dystroglycanopathy with or without Impaired Intellectual Development (Type B) Congenital muscular dystrophy with impaired intellectual development due to defective glycosylation of DAG1 is genetically heterogeneous. See also MDDGB2 (613156), caused by mutation in the POMT2 gene (607439); MDDGB3 (613151), caused by mutation in the POMGNT1 gene (606822); MDDGB4 (613152), caused by mutation in the FKTN gene (607440); MDDGB5 (616612), caused by mutation in the FKRP gene (606596); MDDGB6 (608840), caused by mutation in the LARGE gene (603590); MDDGB14 (615351), caused by mutation in the GMPPB gene (615320); and MDDGB15 (618992), caused by mutation in the DPM3 gene (605951).

Childhood- or juvenile-onset osteoporosis with developmental delay (OPDD) is characterized by evidence of osteopenia or osteoporosis, with recurrent fractures following minor trauma in some patients. Developmental delay is variable, and includes mild intellectual or learning disabilities as well as wide-based gait and/or gross motor delays. Microcephaly is present in some patients (Marom et al., 2021).