Infantile speech, pedolalia, baby talk, infantile perseveration, or infantilism is a speech disorder, persistence of early speech development stage beyond the age when it is normally expected. It is characterized by the omission of some sounds and the substitution of standard speech sounds observed in children in early developmental stages.

The prognosis for children with LKS varies. Some affected children may have a permanent severe language disorder, while others may regain much of their language abilities (although it may take months or years). In some cases, remission and relapse may occur. The prognosis is improved when the onset of the disorder is after age 6 and when speech therapy is started early. Seizures generally disappear by adulthood. Short-term remissions are not uncommon in LKS but they create difficulties in evaluating a patient's response to various therapeutic modalities.

The following table demonstrate the Long-Term Follow-up of Acquired Epileptic Aphasia across many different instrumental studies:.

Lower rates of good outcomes have been reported, ranging between 14% to 50%. Duran "et al." used 7 patients in his study (all males, aged 8–27 years of age) with LKS. On long-term followup, most of his patients did not demonstrate total epilepsy remission and language problems continued. Out of the seven patients, one reported a normal quality of life while the other six reported aphasia to be a substantial struggle. The Duran "et al." study is one of few that features long-term follow up reports of LKS and utilizes EEG testing, MRIs, the Vineland Adaptive Behavior Scales, the Connor's Rating Scales-revised, and a Short-Form Health Survey to analyze its patients.

Globally, more than 200 cases of acquired epileptic aphasia have been described in the literature. Between 1957 and 1980, 81 cases of acquired epileptic aphasia were reported, with 100 cases generally being diagnosed every 10 years.

It is estimated that 25 to 50% of children diagnosed with Autism Spectrum Disorder (ASD) never develop spoken language beyond a few words or utterances. Despite the growing field of research on ASD, there is not much information available pertaining to individuals with autism who never develop functional language; that, in fact, individuals with nonverbal autism are considered to be underrepresented in all of autism research. Because of the limited research on nonverbal autism, there are not many validated measurements appropriate for this population. For example, while they may be appropriate for younger children, they lack the validity for grade-school aged children and adolescents and have continued to be a roadblock for nonverbal autism research. Often in autism research, individuals with nonverbal autism are sub-grouped with LFA, categorized by learning at most one word or having minimal verbal language.

Most of the existing body of research in nonverbal autism focuses on early interventions that predict successful language outcomes. Research suggests that most spoken language is inherited before the age of five, and the likelihood of acquiring functional language in the future past this age is minimal, that early language development is crucial to educational achievement, employment, independence during adulthood, and social relationships.

Landau–Kleffner syndrome (LKS)—also called infantile acquired aphasia, acquired epileptic aphasia or aphasia with convulsive disorder—is a rare childhood neurological syndrome.

It is named after William Landau and Frank Kleffner, who characterized it in 1957 with a diagnosis of six children.

Nonverbal autism is a subset of autism where the subject is unable to speak. While most autistic children eventually begin to speak, there is a significant minority who will remain nonverbal.

Messner "et al." studied ankyloglossia and infant feeding. Thirty-six infants with ankyloglossia were compared to a control group without ankyloglossia. The two groups were followed for six months to assess possible breastfeeding difficulties; defined as nipple pain lasting more than six weeks, or infant difficulty latching onto or staying onto the mother’s breast. Twenty-five percent of mothers of infants with ankyloglossia reported breastfeeding difficulty compared with only 3% of the mothers in the control group. The study concluded that ankyloglossia can adversely affect breastfeeding in certain infants. Infants with ankyologlossia do not, however, have such big difficulties when feeding from a bottle. Limitations of this study include the small sample size and the fact that the quality of the mother’s breastfeeding was not assessed.

Wallace and Clark also studied breastfeeding difficulties in infants with ankyloglossia. They followed 10 infants with ankyloglossia who underwent surgical tongue tie division. Eight of the ten mothers experienced poor infant latching onto the breast, 6/10 experienced sore nipples and 5/10 experienced continual feeding cycles; 3/10 mothers were exclusively breastfeeding. Following a tongue-tie division, 4/10 mothers noted immediate improvements in breastfeeding, 3/10 mothers did not notice any improvements and 6/10 mothers continued breastfeeding for at least four months after the surgery. The study concluded that tongue-tie division may be a possible benefit for infants experiencing breastfeeding difficulties due to ankyloglossia and further investigation is warranted. The limitations of this study include the small sample size and the fact that there was not a control group. In addition, the conclusions were based on subjective parent report as opposed to objective measures.

Opinion varies regarding how frequently ankyloglossia truly causes problems. Some professionals believe it is rarely symptomatic, whereas others believe it is associated with a variety of problems. The disagreement among professionals was documented in a study by Messner and Lalakea (2000). The authors sent a survey to a total of 1598 otolaryngologists, pediatricians, speech-language pathologists and lactation consultants with questions to ascertain their beliefs on ankyloglossia. 797 of the surveys were fully completed and used in the study. It was found that 69% of lactation consultants, but only a minority of pediatricians answered that ankyloglossia is frequently associated with feeding difficulties; 60% of otolaryngologists and 50% of speech pathologists answered that ankyloglossia is sometimes associated with speech difficulties compared to only 23% of pediatricians; 67% of otolaryngologists compared with 21% of pediatricians answered that ankyloglossia is sometimes associated with social and mechanical difficulties. Limitations of this study include a reduced sample size due to unreturned or incomplete surveys.

Infantile neuroaxonal dystrophy is a rare pervasive developmental disorder that primarily affects the nervous system. Individuals with infantile neuroaxonal dystrophy typically do not have any symptoms at birth, but between the ages of about 6 and 18 months they begin to experience delays in acquiring new motor and intellectual skills, such as crawling or beginning to speak. Eventually they lose previously acquired skills.

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene ("PLA2G6") in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.

It is still unknown which bio-chemical mechanisms lead to the occurrence of West syndrome. It is conjectured that it is a malfunction of neurotransmitter function, or more precisely, a malfunction in the regulation of the GABA transmission process. Another possibility being researched is a hyper-production of the Corticotropin-releasing hormone (CRH). It is possible that more than one factor is involved. Both hypotheses are supported by the effect of certain medications used to treat West syndrome.

Cases of epilepsy have been historically divided into three different groups: symptomatic, cryptogenic, and unknown. The International League Against Epilepsy (ILAE) recommended in 2011 to abandon these terms for reasons of clarity and instead try to place individual cases into one of the following 3 groups: genetic, structural/metabolic, and unknown. The new terms are more immediately clear in their meaning, except that the structural and metabolic group includes cases that have a genetic component that does not always directly lead to the condition. Only the genetic grouping has a known direct genetic cause. "Unknown" cases may be of "unknown" genetic, structural, metabolic, or other unknown cause.

The old terminology was defined by the ILAE as follows:

- symptomatic: the epilepsy is the consequence of a known or suspected disorder of the central nervous system.

- cryptogenic: this refers to a disorder whose cause is hidden or occult. Cryptogenic epilepsies are presumed to be symptomatic.

- idiopathic: there is no underlying cause other than a possible hereditary predisposition.

The remainder of this section will refer to the older terminology.

It is not possible to make a generalised prognosis for development due to the variability of causes, as mentioned above, the differing types of symptoms and cause. Each case must be considered individually.

The prognosis for children with idiopathic West syndrome are mostly more positive than for those with the cryptogenic or symptomatic forms. Idiopathic cases are less likely to show signs of developmental problems before the attacks begin, the attacks can often be treated more easily and effectively and there is a lower relapse rate. Children with this form of the syndrome are less likely to go on to develop other forms of epilepsy; around two in every five children develop at the same rate as healthy children.

In other cases, however, treatment of West syndrome is relatively difficult and the results of therapy often dissatisfying; for children with symptomatic and cryptogenic West syndrome, the prognosis is generally not positive, especially when they prove resistant to therapy.

Statistically, 5 out of every 100 children with West syndrome do not survive beyond five years of age, in some cases due to the cause of the syndrome, in others for reasons related to their medication. Only less than half of all children can become entirely free from attacks with the help of medication. Statistics show that treatment produces a satisfactory result in around three out of ten cases, with only one in every 25 children's cognitive and motoric development developing more or less normally.

A large proportion (up to 90%) of children suffer severe physical and cognitive impairments, even when treatment for the attacks is successful. This is not usually because of the epileptic fits, but rather because of the causes behind them (cerebral anomalies or their location or degree of severity). Severe, frequent attacks can (further) damage the brain.

Permanent damage often associated with West syndrome in the literature include cognitive disabilities, learning difficulties and behavioural problems, cerebral palsy (up to 5 out of 10 children), psychological disorders and often autism (in around 3 out of 10 children). Once more, the cause of each individual case of West syndrome must be considered when debating cause and effect.

As many as 6 out of 10 children with West syndrome suffer from epilepsy later in life. Sometimes West syndrome turns into a focal or other generalised epilepsy. Around half of all children develop Lennox-Gastaut syndrome.

In utero exposure to cocaine and other street drugs can lead to porencephaly.

From recent studies, de novo and inherited mutations in the gene "COL4A1", suggesting genetic predisposition within the family, that encodes type IV collagen α1 chain has shown to be associated with and present in patients with porencephaly. "COL4A1" mutation causes a variety of phenotypes, including porencephaly, infantile hemiplegia, and cerebral small vessel diseases involving both stroke and infarction. Abnormal gene expression of "COL4A1" can contribute to the development of porencephaly. "COL4A1" gene expresses a type IV collagen (basement protein) that is present in all tissue and blood vessels and is extremely important for the structural stability of vascular basement membranes. The "COL4A1" protein provides a strong layer around blood vessels. The mutation can weaken the blood vessels within the brain, elevating the probability of a hemorrhage, and eventually promoting internal bleeding then leading to porencephaly during neurodevelopment of infantile stage. Therefore, the formation of cavities can be a result of hemorrhages which promote cerebral degeneration. In a mouse model, mouse with "COL4A1" mutations displayed cerebral hemorrhage, porencephaly, and abnormal development of vascular basement membranes, such as uneven edges, inconsistent shapes, and highly variable thickness. Purposely causing a mutation in the "COL4A1" gene caused several mouse to develop cerebral hemorrhage and porencephaly-like diseases. Though, there is no direct correlation between mutations of the "COL4A1" gene, it appears that it has an influential effect on the development of porencephaly.

Another genetic mutation, "factor V G1691A" mutation, has been reported to show possible association to the development of porencephaly. A mutation in "factor V G1691A" increases the risk of thrombosis, blood clots, in neonates, infants, and children. Therefore, 76 porencephalic and 76 healthy infants were investigated for "factor V G1691A" mutation along with other different prothrombotic risk factors. The results indicated that there was higher prevalence of the "factor V G1691A" mutation in the porencephalic patient group. The prediction that childhood porencephaly is caused by hypercoagulable state, a condition where one has a higher chance of developing blood clots, was supported by the significance of the "factor V G1691A" mutation. Also, pregnant women in hypercoagulable state can cause the fetus to have the same risks, therefore possibly causing fetal loss, brain damage, lesions, and infections that lead to porencephaly. However, other different prothrombotic risk factors individually did not reach statistical significance to link it to the development of porencephaly, but a combination of multiple prothrombotic risk factors in the porencephaly group was significant. Overall, "factor V G1691A" mutation has been linked to the development of porencephaly. However, this one mutation is not the cause of porencephaly, and whether further prothrombiotic risk factors are associated with porencephaly still remains unknown.

Infantile neuronal ceroid lipofuscinoses (INCL) or Santavuori disease or Hagberg-Santavuori disease or Santavuori-Haltia disease or Infantile Finnish type neuronal ceroid lipofuscinosis or Balkan disease is a form of NCL and inherited as a recessive autosomal genetic trait. The disorder is progressive, degenerative and fatal, extremely rare worldwide – with approximately 60 official cases reported by 1982, perhaps 100 sufferers in total today – but relatively common in Finland due to the local founder effect.

The syndrome primarily affects young males. Preliminary studies suggest that prevalence may be 1.8 per 10,000 live male births. 50% of those affected do not live beyond 25 years of age, with deaths attributed to the impaired immune function.

Infantile Progressive Bulbar palsy is a rare type of progressive bulbar palsy that occurs in children. The disease exists in both rapid and slow onsets, and involves inflammation of the gray matter of the bulb. Infantile PBP is a disease that manifests itself in two forms: Fazio Londe syndrome (FL) and Brown-Vialetto-Van-Laere syndrome (BVVL).

In affected individuals presenting with the ICCA syndrome, the human genome was screened with microsatellite markers regularly spaced, and strong evidence of linkage with the disease was obtained in the pericentromeric region of chromosome 16, with a maximum lod score, for D16S3133 of 6.76 at a recombination fraction of 0. The disease gene has been mapped at chromosome 16p12-q12.This linkage has been confirmed by different authors. The chromosome 16 ICCA locus shows complicated genomic architecture and the ICCA gene remains unknown.

Infantile convulsions and choreoathetosis (ICCA) syndrome is a neurological genetic disorder with an autosomal dominant mode of inheritance. It is characterized by the association of benign familial infantile epilepsy (BIFE) at age 3–12 months and later in life with paroxysmal kinesigenic choreoathetosis. The ICCA syndrome was first reported in 1997 in four French families from north-western France and provided the first genetic evidence for common mechanisms shared by benign infantile seizures and paroxysmal dyskinesia. The epileptic origin of PKC has long been a matter of debates and PD have been classified as reflex epilepsies.Indeed, attacks of PKC and epileptic seizures have several characteristics in common, they both are paroxysmal in presentation with a tendency to spontaneous remission, and a subset of PKC responds well to anticonvulsants. This genetic disease has been mapped to chromosome 16p-q12. More than 30 families with the clinical characteristics of ICCA syndrome have been described worldwide so far.

A feeding disorder in infancy or early childhood is a child's refusal to eat certain food groups, textures, solids or liquids for a period of at least one month, which causes the child to not gain enough weight, grow naturally, or cause any developmental delays. Feeding disorders resemble failure to thrive, except that at times in feeding disorder there is no medical or physiological condition that can explain the very small amount of food the children consume or their lack of growth. Some of the times a previous medical condition that has been resolved is causing the issue.

The development of children born with INCL is normal for the first 8–18 months, but will then flounder and start to regress both physically and mentally. Motor skills and speech are lost, and optic atrophy causes blindness. A variety of neurological symptoms, such as epilepsy and myoclonic seizures, appear. The senses of hearing and touch remain unaffected. The average lifespan of an INCL child is 9–11 years.

Aicardi syndrome is a rare genetic malformation syndrome characterized by the partial or complete absence of a key structure in the brain called the corpus callosum, the presence of retinal abnormalities, and seizures in the form of infantile spasms. Aicardi syndrome is theorized to be caused by a defect on the X chromosome as it has thus far only been observed in girls or in boys with Klinefelter syndrome. Confirmation of this theory awaits the discovery of a causative gene. Symptoms typically appear before a baby reaches about 5 months of age.

The prognosis varies widely from case to case, depending on the severity of the symptoms. However, almost all people reported with Aicardi syndrome to date have experienced developmental delay of a significant degree, typically resulting in mild to moderate to profound intellectual disability. The age range of the individuals reported with Aicardi syndrome is from birth to the mid 40s.

There is no cure for this syndrome.

M2DS is one of the several types of X-linked intellectual disability. The cause of M2DS is a duplication of the MECP2 or Methyl CpG binding protein 2 gene located on the X chromosome (Xq28). The MeCP2 protein plays a pivotal role in regulating brain function. Increased levels of MECP2 protein results in abnormal neural function and impaired immune system. Mutations in the MECP2 gene are also commonly associated with Rett syndrome in females. Advances in genetic testing and more widespread use of Array Comparative Genomic Hybridization has led to increased diagnosis of MECP2 duplication syndrome. It is thought to represent ~1% of X-linked male mental disability cases.

Benign familial infantile epilepsy (BFIE), also known as benign familial infantile seizures (BFIS) or benign familial infantile convulsions (BFIC) is an epilepsy syndrome. Affected children, who have no other health or developmental problems, develop seizures during infancy. These seizures have focal origin within the brain but may then spread to become generalised seizures. The seizures may occur several times a day, often grouped in clusters over one to three days followed by a gap of one to three months. Treatment with anticonvulsant drugs is not necessary but they are often prescribed and are effective at controlling the seizures. This form of epilepsy resolves after one or two years, and appears to be completely benign. The EEG of these children, between seizures, is normal. The brain appears normal on MRI scan.

A family history of epilepsy in infancy distinguishes this syndrome from the non-familial classification (see benign infantile epilepsy), though the latter may be simply sporadic cases of the same genetic mutations. The condition is inherited with an autosomal dominant transmission. There are several genes responsible for this syndrome, on chromosomes 2, 16 and 19. It is generally described as idiopathic, meaning that no other neurological condition is associated with it or causes it. However, there are some forms that are linked to neurological conditions. One variant known as infantile convulsions and choreoathetosis (ICCA) forms an association between BFIE and paroxysmal kinesigenic choreoathetosis and has been linked to the PRRT2 gene on chromosome 16. An association with some forms of familial hemiplegic migraine (FHM) has also been found. Benign familial infantile epilepsy is not genetically related to benign familial neonatal epilepsy (BFNE), which occurs in neonates. However, a variation with seizure onset between two days and seven months called "benign familial neonatal–infantile seizures" (BFNIS) has been described, which is due to a mutation in the SCN2A gene.

No single cause of OS has been identified. In most cases, there is severe atrophy of both hemispheres of the brain. Less often, the root of the disorder is an underlying metabolic syndrome. Although it was initially published that no genetic connection had been established, several genes have since associated with Ohtahara syndrome. It can be associated with mutations in "ARX", "CDKL5", "SLC25A22", "STXBP1", "SPTAN1", "KCNQ2", "ARHGEF9", "PCDH19", "PNKP", "SCN2A", "PLCB1", "SCN8A", and likely others.

Treatment outlook is poor. Anticonvulsant drugs and glucocorticoid steroids may be used to try to control the seizures, but their effectiveness is limited. Most therapies are related to symptoms and day-to-day living.