The severity of different forms of PCH varies, but many children inheriting the mutated gene responsible do not survive infancy or childhood; nevertheless, some individuals born with PCH have reached adulthood.

NPCA is a syndrome and can have diverse causes. It has a genetic basis and inheritance is considered to be autosomal recessive. However, autosomal dominant variety has also been reported. There may be familial balanced translocation t(8;20)(p22;q13) involved.

In most cases, between the age of 2 and 4 oculomotor signals are present. Between the age of 2 and 8, telangiectasias appears. Usually by the age of 10 the child needs a wheel chair. Individuals with autosomal recessive cerebellum ataxia usually survive till their 20s; in some cases individuals have survived till their 40s or 50s.

Genetic

- Inborn errors of metabolism

1. Congenital disorder of glycosylation

2. Mitochondrial disorders

3. Peroxisomal disorder

4. Glucose transporter defect

5. Menkes disease

6. Congenital disorders of amino acid metabolism

7. Organic acidemia

Syndromes

- Contiguous gene deletion

1. 17p13.3 deletion (Miller–Dieker syndrome)

- Single gene defects

1. Rett syndrome (primarily girls)

2. Nijmegen breakage syndrome

3. X-linked lissencephaly with abnormal genitalia

4. Aicardi–Goutières syndrome

5. Ataxia telangiectasia

6. Cohen syndrome

7. Cockayne syndrome

Acquired

- Disruptive injuries

1. Traumatic brain injury

2. Hypoxic-ischemic encephalopathy

3. Ischemic stroke

4. Hemorrhagic stroke

- Infections

1. Congenital HIV encephalopathy

2. Meningitis

3. Encephalitis

- Toxins

1. Lead poisoning

2. Chronic renal failure

- Deprivation

1. Hypothyroidism

2. Anemia

3. Congenital heart disease

4. Malnutrition

Genetic factors may play a role in causing some cases of microcephaly. Relationships have been found between autism, duplications of chromosomes, and macrocephaly on one side. On the other side, a relationship has been found between schizophrenia, deletions of chromosomes, and microcephaly. Moreover, an association has been established between common genetic variants within known microcephaly genes ("MCPH1, CDK5RAP2") and normal variation in brain structure as measured with magnetic resonance imaging (MRI)i.e., primarily brain cortical surface area and total brain volume.

The spread of Aedes mosquito-borne Zika virus has been implicated in increasing levels of congenital microcephaly by the International Society for Infectious Diseases and the US Centers for Disease Control and Prevention. Zika can spread from a pregnant woman to her fetus. This can result in other severe brain malformations and birth defects. A study published in The New England Journal of Medicine has documented a case in which they found evidence of the Zika virus in the brain of a fetus that displayed the morphology of microcephaly.

Pontocerebellar hypoplasia (PCH) is a heterogeneous group of rare neurodegenerative disorders caused by genetic mutations and characterised by progressive atrophy of various parts of the brain such as the cerebellum or brainstem (particularly the pons). Where known, these disorders are inherited in an autosomal recessive fashion. There is no known cure for PCH.

Mental retardation and microcephaly with pontine and cerebellar hypoplasia (MICPCH), also known as Mental retardation, X-linked, syndromic, Najm type (MRXSNA), is a rare genetic disorder of infants characterised by intellectual disability and pontocerebellar hypoplasia.

The disorder is associated with a mutation in the "CASK" gene which is transmitted in an X-linked manner. As with the vast majority of genetic disorders, there is no known cure to MICPCH.

The following values seem to be aberrant in children with CASK gene defects: lactate, pyruvate, 2-ketoglutarate, adipic acid and suberic acid, which seems to backup the proposal that CASK affects mitochondrial function. It is also speculated that phosphoinositide 3-kinase in the inositol metabolism is impacted in the disease, causing folic acid metabolization problems.

Prognosis varies widely depending on severity of symptoms, degree of intellectual impairment, and associated complications. Because the syndrome is rare and so newly identified, there are no long term studies.

Non-progressive congenital ataxia (NPCA) is a non-progressive form of cerebellar ataxia which can occur with or without cerebellar hypoplasia.

Aicardi–Goutières syndrome (AGS), which is completely distinct from the similarly named Aicardi syndrome, is a rare, usually early onset childhood, inflammatory disorder most typically affecting the brain and the skin (neurodevelopmental disorder). The majority of affected individuals experience significant intellectual and physical problems, although this is not always the case. The clinical features of AGS can mimic those of "in utero" acquired infection, and some characteristics of the condition also overlap with the autoimmune disease systemic lupus erythematosus (SLE). Following an original description of eight cases in 1984, the condition was first referred to as 'Aicardi–Goutières syndrome' (AGS) in 1992, and the first international meeting on AGS was held in Pavia, Italy, in 2001.

AGS can occur due to mutations in any one of a number of different genes, of which seven have been identified to date, namely: TREX1, RNASEH2A, RNASEH2B, RNASEH2C (which together encode the Ribonuclease H2 enzyme complex), SAMHD1, ADAR1, and IFIH1 (coding for MDA5). This neurological disease occurs in all populations worldwide, although it is almost certainly under-diagnosed. To date (2014) at least 400 cases of AGS are known.

Isolated

1. Familial (autosomal recessive) microcephaly

2. Autosomal dominant microcephaly

3. X-linked microcephaly

4. Chromosomal (balanced rearrangements and ring chromosome)

Syndromes

- Chromosomal

1. Poland syndrome

2. Down syndrome

3. Edward syndrome

4. Patau syndrome

5. Unbalanced rearrangements

- Contiguous gene deletion

1. 4p deletion (Wolf–Hirschhorn syndrome)

2. 5p deletion (Cri-du-chat)

3. 7q11.23 deletion (Williams syndrome)

4. 22q11 deletion (DiGeorge syndrome)

- Single gene defects

1. Smith–Lemli–Opitz syndrome

2. Seckel syndrome

3. Cornelia de Lange syndrome

4. Holoprosencephaly

5. Primary microcephaly 4

6. Wiedemann-Steiner syndrome

Acquired

- Disruptive injuries

1. Ischemic stroke

2. Hemorrhagic stroke

3. Death of a monozygotic twin

- Vertically transmitted infections

1. Congenital cytomegalovirus infection

2. Toxoplasmosis

3. Congenital rubella syndrome

4. Zika virus

- Drugs

1. Fetal hydantoin syndrome

2. Fetal alcohol syndrome

Other

1. Radiation exposure to mother

2. Maternal malnutrition

3. Maternal phenylketonuria

4. Poorly controlled gestational diabetes

5. Hyperthermia

6. Maternal hypothyroidism

7. Placental insufficiency

The prognosis of this developmental disorder is highly based on the underlying disorder. Cerebellar hypoplasia may be progressive or static in nature. Some cerebellar hypoplasia resulting from congenital brain abnormalities/malformations are not progressive. Progressive cerebellar hypoplasia is known for having poor prognosis, but in cases where this disorder is static, prognosis is better.

There is no known prevention of spinocerebellar ataxia. Those who are believed to be at risk can have genetic sequencing of known SCA loci performed to confirm inheritance of the disorder.

In terms of frequency, is estimated at 2 per 100,000, it has identified in different regions of the world. Some clusters of certain types of autosomal dominant cerebellar ataxia reach a prevalence of 5 per 100,000.

The clinical course of BVVL can vary from one patient to another. There have been cases with progressive deterioration, deterioration followed by periods of stabilization, and deterioration with abrupt periods of increasing severity.

The syndrome has previously been considered to have a high mortality rate but the initial response of most patients to the Riboflavin protocol are very encouraging and seem to indicate a significantly improved life expectancy could be achievable. There are three documented cases of BVVL where the patient died within the first five years of the disease. On the contrary, most patients have survived more than 10 years after the onset of their first symptom, and several cases have survived 20–30 years after the onset of their first symptom.

Families with multiple cases of BVVL and, more generally, multiple cases of infantile progressive bulbar palsy can show variability in age of disease onset and survival. Dipti and Childs described such a situation in which a family had five children that had Infantile PBP. In this family, three siblings showed sensorineural deafness and other symptoms of BVVL at an older age. The other two siblings showed symptoms of Fazio-Londe disease and died before the age of two.

Laboratory: normal metabolic and infective screening. An increase in the number of white cells (particularly lymphocytes) in the CSF, and high levels of interferon-alpha activity and neopterin in the CSF are important clues - however, these features are not always present. More recently, a persistent elevation of mRNA levels of interferon-stimulated gene transcripts have been recorded in the peripheral blood of almost all cases of AGS with mutations in "TREX1", "RNASEH2A", "RNASEH2C", "SAMHD1", "ADAR1" and "IFIH1", and in 75% of patients with mutations in "RNASEH2B". These results are irrespective of age. Thus, this interferon signature appears to be a very good marker of disease.

Genetics: pathogenic mutations in any of the seven genes known to be involved in AGS.

Microlissencephaly is listed in Orphanet database as a rare disease. There is no much information available about the epidemiology of microlissencepahly in literature. A PhD thesis has estimated the prevalence of microlissencepahly in South–Eastern Hungary between July 1992 and June 2006 to be a case every 91,000 live births (0.11:10,000).

Nicolaides–Baraitser syndrome (NCBRS) is a rare genetic condition caused by de novo missense mutations in the SMARCA2 gene and has only been reported in less than 100 cases worldwide. NCBRS is a distinct condition and well recognizable once the symptoms have been identified.

Spinal muscular atrophy with progressive myoclonic epilepsy (SMA-PME), sometimes called Jankovic–Rivera syndrome, is a very rare neurodegenerative disease whose symptoms include slowly progressive muscle wasting (atrophy), predominantly affecting distal muscles, combined with denervation and myoclonic seizures.

SMA-PME is associated with a missense mutation (c.125C→T) or deletion in exon 2 of the "ASAH1" gene and is inherited in an autosomal recessive manner. As with many genetic disorders, there is no known cure to SMA-PME.

The condition was first described in 1979 by American researchers Joseph Jankovic and Victor M. Rivera.

In at least some case, the gene lesion involves a mutation in the "CSB" gene.

It can be associated with "ERCC6".

Mosaic mutations in PIK3CA have been found to be the genetic cause of M-CM. Genetic testing for the mutation is currently only available on a research basis. Other overgrowth conditions with distinct phenotypes have also been found to be caused by mosaic mutations in PIK3CA. How different mutations in this gene result in a variety of defined clinical syndromes is still being clarified. Mutations in PIK3CA have not been found in a non-mosaic state in any of these disorders, so it is unlikely that the conditions could be inherited.

Behr syndrome is characterized by the association of early-onset optic atrophy with spinocerebellar degeneration resulting in ataxia, pyramidal signs, peripheral neuropathy and developmental delay.

Although it is an autosomal recessive disorder, heterozygotes may still manifest much attenuated symptoms. Autosomal dominant inheritance also being reported in a family. Recently a variant of OPA1 mutation with phenotypic presentation like Behr syndrome is also described. Some reported cases have been found to carry mutations in the OPA1, OPA3 or C12ORF65 genes which are known causes of pure optic atrophy or optic atrophy complicated by movement disorder.

The disorder has been associated with various mutations in the SLC52A2 and "SLC52A3" genes. This gene is thought to be involved in transport of riboflavin.

BVVL is allelic and phenotypically similar to Fazio–Londe disease and likewise is inherited in an autosomal recessive manner.

Treatment of Ramsay Hunt Syndrome Type 1 is specific to individual symptoms. Myoclonus and seizures may be treated with drugs like valproate.

Some have described this condition as difficult to characterize.

Gillespie syndrome, also called aniridia, cerebellar ataxia and mental deficiency. is a rare genetic disorder. The disorder is characterized by partial aniridia (meaning that part of the iris is missing), ataxia (motor and coordination problems), and, in most cases, intellectual disability. It is heterogeneous, inherited in either an autosomal dominant or autosomal recessive manner. Gillespie syndrome was first described by American ophthalmologist Fredrick Gillespie in 1965.

DeSanctis–Cacchione syndrome is an extremely rare disorder characterized by the skin and eye symptoms of xeroderma pigmentosum (XP) occurring in association with microcephaly, progressive mental retardation, retarded growth and sexual development, deafness, choreoathetosis, ataxia and quadriparesis.