Dandy-Walker malformation (DWM) is defined by hypoplasia and upward rotation of the cerebellar vermis and cystic dilation of the fourth ventricle. Affected individuals often have motor deficits such as delayed motor development, hypotonia, and ataxia; about half have impaired intellectual development and some have hydrocephalus. DWM is a heterogeneous disorder. The low empiric recurrence risk of approximately 1 to 2% for nonsyndromic DWM suggests that mendelian inheritance is unlikely (summary by Murray et al., 1985).

Branchiooculofacial syndrome (BOFS) is characterized by branchial (cervical or infra- or supra-auricular) skin defects that range from barely perceptible thin skin or hair patch to erythematous "hemangiomatous" lesions to large weeping erosions; ocular anomalies that can include microphthalmia, anophthalmia, coloboma, cataract, and nasolacrimal duct stenosis/atresia; and facial anomalies that can include dolichocephaly, hypertelorism or telecanthus, broad nasal tip, upslanted palpebral fissures, cleft lip or prominent philtral pillars that give the appearance of a repaired cleft lip (formerly called "pseudocleft lip") with or without cleft palate, upper lip pits, and lower facial weakness (asymmetric crying face or partial weakness of cranial nerve VII). Malformed and prominent pinnae and hearing loss from inner ear and/or petrous bone anomalies are common. Intellect is usually normal.

Gomez-Lopez-Hernandez syndrome (GLHS), also known as cerebellotrigeminal dermal dysplasia, is a rare neurocutaneous syndrome classically characterized by the triad of rhombencephalosynapsis, trigeminal anesthesia, often giving rise to corneal opacities, and bilateral parietal or parietooccipital alopecia. However, trigeminal anesthesia is an inconsistent finding (summary by Sukhudyan et al., 2010).

Porencephaly-cerebellar hypoplasia-internal malformations syndrome is rare central nervous system malformation syndrome characterized by bilateral porencephaly, absence of the septum pellucidum and cerebellar hypoplasia with absent vermis. Additionally, dysmorphic facial features (hypertelorism, epicanthic folds, high arched palate, prominent metopic suture), macrocephaly, corneal clouding, situs inversus, tetralogy of Fallot, atrial septal defects and/or seizures have been observed.

Permanent neonatal diabetes mellitus-pancreatic and cerebellar agenesis syndrome is characterized by neonatal diabetes mellitus associated with cerebellar and/or pancreatic agenesis.

Joubert syndrome is a genetically heterogeneous autosomal recessive disorder characterized by a specific hindbrain malformation, which is referred to as the 'molar tooth sign' (MTS) on brain MRI, hypotonia, developmental delay, oculomotor apraxia, and breathing abnormalities. The complex brainstem malformation consists of cerebellar vermian hypoplasia/aplasia, thickened and reoriented superior cerebellar peduncles, and an abnormally large interpeduncular fossa, giving the appearance of a molar tooth on transaxial slices (Maria et al., 1997). Additional features sometimes associated with Joubert syndrome include retinal anomalies, polydactyly, hepatic fibrosis, and renal disease. These related disorders are often referred to as 'cerebellooculorenal syndromes' (CORSs) (Chance et al., 1999; Satran et al., 1999).

Arima syndrome is an autosomal recessive disorder characterized by agenesis of the cerebellar vermis, ocular abnormalities, cystic kidney disease, and, in some cases, liver disease. It shares phenotypic features with Joubert syndrome (see 213300), COACH syndrome (see 216360), and familial juvenile nephronophthisis (see 256100).

A syndromic disorder with the association between Dandy-Walker malformation and postaxial polydactyly as a major feature. The Dandy-Walker malformation has a variable expression and characteristics of a posterior fossa cyst communicating with the fourth ventricle, the partial or complete absence of the cerebellar vermis, and facultative hydrocephalus. Postaxial polydactyly includes tetramelic postaxial polydactyly of hands and feet with possible enlargement of the fifth metacarpal and metatarsal bones, as well as bifid fifth metacarpals.

Any Joubert syndrome in which the cause of the disease is a mutation in the CEP290 gene.

Hepatic fibrosis-renal cysts-intellectual disability syndrome is a rare, syndromic intellectual disability characterized by early developmental delay with failure to thrive, intellectual disability, congenital hepatic fibrosis, renal cystic dysplasia, and dysmorphic facial features (bilateral ptosis, anteverted nostrils, high arched palate, and micrognathia). Variable additional features have been reported, including cerebellar anomalies, postaxial polydactyly, syndactyly, genital anomalies, tachypnea. There have been no further descriptions in the literature since 1987.

RNU4atac-opathy encompasses the phenotypic spectrum of biallelic RNU4ATAC pathogenic variants, including the three historically designated clinical phenotypes microcephalic osteodysplastic primordial dwarfism type I/III (MOPDI), Roifman syndrome, and Lowry-Wood syndrome, as well as varying combinations of the disease features / system involvement that do not match specific defined phenotypes. Findings present in all affected individuals include growth restriction, microcephaly, skeletal dysplasia, and cognitive impairment. Less common but variable findings include brain anomalies, seizures, strokes, immunodeficiency, and cardiac anomalies, as well as ophthalmologic, skin, renal, gastrointestinal, hearing, and endocrine involvement.

Mevalonic aciduria (MEVA), the first recognized defect in the biosynthesis of cholesterol and isoprenoids, is a consequence of a deficiency of mevalonate kinase (ATP:mevalonate 5-phosphotransferase; EC 2.7.1.36). Mevalonic acid accumulates because of failure of conversion to 5-phosphomevalonic acid, which is catalyzed by mevalonate kinase. Mevalonic acid is synthesized from 3-hydroxy-3-methylglutaryl-CoA, a reaction catalyzed by HMG-CoA reductase (142910). Mevalonic aciduria is characterized by dysmorphology, psychomotor retardation, progressive cerebellar ataxia, and recurrent febrile crises, usually manifesting in early infancy, accompanied by hepatosplenomegaly, lymphadenopathy, arthralgia, and skin rash. The febrile crises are similar to those observed in hyperimmunoglobulinemia D and to periodic fever syndrome (HIDS; 260920), which is also caused by mutation in the MVK gene (summary by Prietsch et al., 2003).

Syndrome with characteristics of severe psychomotor retardation, failure to thrive and intolerance to wheat and dairy products. So far, only two cases have been described. The disease is caused by mutations in the COG8 gene, which encodes a subunit of the COG complex. This complex is involved vesicle transport in the Golgi apparatus.

Meckel syndrome is an autosomal recessive pre- or perinatal lethal disorder characterized by a combination of renal cysts and variably associated features including developmental anomalies of the central nervous system (typically occipital encephalocele), hepatic ductal dysplasia and cysts, and postaxial polydactyly (summary by Baala et al., 2007). For a more complete phenotypic description and information on genetic heterogeneity of Meckel syndrome, see MKS1 (249000).

Congenital muscular dystrophy-dystroglycanopathy with brain and eye anomalies (type A), which includes both the more severe Walker-Warburg syndrome (WWS) and the slightly less severe muscle-eye-brain disease (MEB), is an autosomal recessive disorder with characteristic brain and eye malformations, profound mental retardation, congenital muscular dystrophy, and death usually in the first years of life. It represents the most severe end of a phenotypic spectrum of similar disorders resulting from defective glycosylation of DAG1 (128239), collectively known as 'dystroglycanopathies' (Beltran-Valero de Bernabe et al., 2004). For a general phenotypic description and a discussion of genetic heterogeneity of muscular dystrophy-dystroglycanopathy type A, see MDDGA1 (236670).

Frontonasal dysplasia-2 (FND2) is an autosomal recessive disorder characterized by variable degrees of alopecia, skull defects, hypertelorism, depressed nasal bridge and ridge with notched alae nasi, and abnormal central nervous system findings (summary by Kariminejad et al., 2014).

Joubert syndrome-14 (JBTS14) is an autosomal recessive developmental disorder characterized by severe mental retardation, hypoplasia of the cerebellar vermis and molar tooth sign (MTS) on brain imaging, hypotonia, abnormal breathing pattern in infancy, and dysmorphic facial features. Additional findings can include renal cysts, abnormal eye movements, and postaxial polydactyly (summary by Boycott et al., 2007 and Huang et al., 2011). For a phenotypic description and a discussion of genetic heterogeneity of Joubert syndrome, see 213300.

Any Joubert syndrome in which the cause of the disease is a mutation in the TCTN3 gene.

Congenital muscular dystrophy-dystroglycanopathy with brain and eye anomalies (type A) is a autosomal recessive disorder associated with severe neurologic defects and resulting in early infantile death. The phenotype includes the alternative clinical designations Walker-Warburg syndrome (WWS) and muscle-eye-brain disease (MEB). The disorder represents the most severe end of a phenotypic spectrum of similar disorders resulting from defective glycosylation of alpha-dystroglycan (DAG1; 128239), collectively known as dystroglycanopathies (summary by Buysse et al., 2013). For a general phenotypic description and a discussion of genetic heterogeneity of muscular dystrophy-dystroglycanopathy type A, see MDDGA1 (236670).

Any Joubert syndrome in which the cause of the disease is a mutation in the PDE6D gene.

A rare genetic developmental defect during embryogenesis malformation syndrome with characteristics of intrauterine growth restriction, flexion arthrogryposis of all joints, severe microcephaly, renal cystic dysplasia/agenesis/hypoplasia and complex malformations of the brain (cerebral and cerebellar hypoplasia, vermis, corpus callosum and/or occipital lobe agenesis, with or without arhinencephaly), as well as of the genitourinary tract (ureteral agenesis/hypoplasia, uterine hypoplasia and/or vaginal atresia), leading to fetal demise.

Joubert syndrome is a clinically and genetically heterogeneous group of disorders characterized by hypoplasia of the cerebellar vermis with the characteristic neuroradiologic 'molar tooth sign,' and accompanying neurologic symptoms, including dysregulation of breathing pattern and developmental delay. Other variable features include retinal dystrophy and renal anomalies (Saraiva and Baraitser, 1992; Valente et al., 2005). Genetic Heterogeneity of Joubert Syndrome See also JBTS2 (608091), caused by mutation in the TMEM216 gene (613277) on chromosome 11q13; JBTS3 (608629), caused by mutation in the AHI1 gene (608894) on chromosome 6q23; JBTS4 (609583), caused by mutation in the NPHP1 gene (607100) on chromosome 2q13; JBTS5 (610188), caused by mutation in the CEP290 gene, also called NPHP6 (610142), on chromosome 12q21; JBTS6 (610688), caused by mutation in the TMEM67 gene (609884) on chromosome 8q21; JBTS7 (611560), caused by mutation in the RPGRIP1L gene (610937) on chromosome 16q12; JBTS8 (612291), caused by mutation in the ARL13B (608922) on chromosome 3q11; JBTS9 (612285), caused by mutation in the CC2D2A gene (612013) on chromosome 4p15; JBTS10 (300804), caused by mutation in the CXORF5 gene (300170) on chromosome Xp22; JBTS11 (see 613820), caused by mutation in the TTC21B gene (612014) on chromosome 2q24; JBTS12 (see 200990), caused by mutation in the KIF7 gene (611254) on chromosome 15q26; JBTS13 (614173), caused by mutation in the TCTN1 gene (609863) on chromosome 12q24; JBTS14 (614424), caused by mutation in the TMEM237 gene (614423) on chromosome 2q33; JBTS15 (614464), caused by mutation in the CEP41 gene (610523) on chromosome 7q32; JBTS16 (614465), caused by mutation in the TMEM138 gene (614459) on chromosome 11q; JBTS17 (614615), caused by mutation in the CPLANE1 gene (614571) on chromosome 5p13; JBTS18 (614815), caused by mutation in the TCTN3 gene (613847) on chromosome 10q24; JBTS19 (see 614844), caused by mutation in the ZNF423 gene (604577) on chromosome 16q12; JBTS20 (614970), caused by mutation in the TMEM231 gene (614949) on chromosome 16q23; JBTS21 (615636), caused by mutation in the CSPP1 gene (611654) on chromosome 8q13; JBTS22 (615665), caused by mutation in the PDE6D gene (602676) on chromosome 2q37; JBTS23 (616490), caused by mutation in the KIAA0586 gene (610178) on chromosome 14q23; JBTS24 (616654), caused by mutation in the TCTN2 gene (613846) on chromosome 12q24; JBTS25 (616781), caused by mutation in the CEP104 gene (616690) on chromosome 1p36; JBTS26 (616784), caused by mutation in the KATNIP gene (616650) on chromosome 16p12; JBTS27 (617120), caused by mutation in the B9D1 gene (614144) on chromosome 17p11; JBTS28 (617121), caused by mutation in the MKS1 gene (609883) on chromosome 17q23; JBTS29 (see 617562), caused by mutation in the TMEM107 gene (616183) on chromosome 17p13; JBTS30 (617622), caused by mutation in the ARMC9 gene (617612) on chromosome 2q37; JBTS31 (617761), caused by mutation in the CEP120 gene (613446) on chromosome 5q23; JBTS32 (617757), caused by mutation in the SUFU gene (607035) on chromosome 10q24; JBTS33 (617767), caused by mutation in the PIBF1 gene (607532) on chromosome 13q21; JBTS34 (see 614175), caused by mutation in the B9D2 gene (611951) on chromosome 19q13; JBTS35 (618161), caused by mutation in the ARL3 gene (604695) on chromosome 10q24; JBTS36 (618763), caused by mutation in the FAM149B1 gene (618413) on chromosome 10q22; JBTS37 (619185), caused by mutation in the TOGARAM1 gene (617618) on chromosome 14q21; JBTS38 (619476), caused by mutation in the KIAA0753 gene (617112) on chromosome 17p13; JBTS39 (619562), caused by mutation in the TMEM218 gene (619285) on chromosome 11q24; and JBTS40 (619582), caused by mutation in the IFT74 gene (608040) on chromosome 9p21.

Autosomal dominant spastic paraplegia-88 (SPG88) is characterized by onset of symptoms in the first year of life. Affected individuals show delayed motor development with walking difficulties due to spasticity of the lower limbs. The disorder is slowly progressive, but variable in severity; some patients are unable to ambulate independently. Most patients have a pure form of the disorder, although rare patients have been reported to have additional features, including peripheral neuropathy, speech delay, ADHD, and nonspecific brain imaging abnormalities (Schob et al., 2021, Estiar et al., 2022, De Winter et al., 2022). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal dominant spastic paraplegia, see SPG3A (182600).