Valinemia is an inborn error of metabolism characterized clinically by vomiting, feeding difficulties, hypotonia, and developmental delay, and biochemically by high concentrations of valine in serum and urine (Wada, 1965).

3-Hydroxy-3-methylglutaryl-CoA lyase deficiency (HMGCLD) is a rare autosomal recessive disorder with the cardinal manifestations of metabolic acidosis without ketonuria, hypoglycemia, and a characteristic pattern of elevated urinary organic acid metabolites, including 3-hydroxy-3-methylglutaric, 3-methylglutaric, and 3-hydroxyisovaleric acids. Urinary levels of 3-methylcrotonylglycine may be increased. Dicarboxylic aciduria, hepatomegaly, and hyperammonemia may also be observed. Presenting clinical signs include irritability, lethargy, coma, and vomiting (summary by Gibson et al., 1988).

Alexander disease, a progressive disorder of cerebral white matter caused by a heterozygous GFAP pathogenic variant, comprises a continuous clinical spectrum most recognizable in infants and children and a range of nonspecific neurologic manifestations in adults. This chapter discusses the spectrum of Alexander disease as four forms: neonatal, infantile, juvenile, and adult. The neonatal form begins in the first 30 days after birth with neurologic findings (e.g., hypotonia, hyperexcitability, myoclonus) and/or gastrointestinal manifestations (e.g., gastroesophageal reflux, vomiting, failure to thrive), followed by severe developmental delay and regression, seizures, megalencephaly, and typically death within two years. The infantile form is characterized by variable developmental issues: initially some have delayed or plateauing of acquisition of new skills, followed in some by a loss of gross and fine motor skills and language during in the first decade or in others a slow disease course that spans decades. Seizures, often triggered by illness, may be less frequent/severe than in the neonatal form. The juvenile form typically presents in childhood or adolescence with clinical and imaging features that overlap with the other forms. Manifestations in early childhood are milder than those in the infantile form (e.g., mild language delay may be the only developmental abnormality or, with language acquisition, hypophonia or nasal speech may alter the voice, often prior to appearance of other neurologic features). Vomiting and failure to thrive as well as scoliosis and autonomic dysfunction are common. The adult form is typically characterized by bulbar or pseudobulbar findings (palatal myoclonus, dysphagia, dysphonia, dysarthria or slurred speech), motor/gait abnormalities with pyramidal tract signs (spasticity, hyperreflexia, positive Babinski sign), or cerebellar abnormalities (ataxia, nystagmus, or dysmetria). Others may have hemiparesis or hemiplegia with a relapsing/remitting course or slowly progressive quadriparesis or quadriplegia. Other neurologic features can include sleep apnea, diplopia or disorders of extraocular motility, and autonomic dysfunction.

Familial hemiplegic migraine (FHM) falls within the category of migraine with aura. In migraine with aura (including FHM) the neurologic symptoms of aura are unequivocally localizable to the cerebral cortex or brain stem and include visual disturbance (most common), sensory loss (e.g., numbness or paresthesias of the face or an extremity), and dysphasia (difficulty with speech). FHM must include motor involvement, such as hemiparesis (weakness of an extremity). Hemiparesis occurs with at least one other symptom during FHM aura. Neurologic deficits with FHM attacks can be prolonged for hours to days and may outlast the associated migrainous headache. FHM is often earlier in onset than typical migraine, frequently beginning in the first or second decade; the frequency of attacks tends to decrease with age. Approximately 40%-50% of families with CACNA1A-FHM have cerebellar signs ranging from nystagmus to progressive, usually late-onset mild ataxia.

Familial hemiplegic migraine (FHM) falls within the category of migraine with aura. In migraine with aura (including FHM) the neurologic symptoms of aura are unequivocally localizable to the cerebral cortex or brain stem and include visual disturbance (most common), sensory loss (e.g., numbness or paresthesias of the face or an extremity), and dysphasia (difficulty with speech). FHM must include motor involvement, such as hemiparesis (weakness of an extremity). Hemiparesis occurs with at least one other symptom during FHM aura. Neurologic deficits with FHM attacks can be prolonged for hours to days and may outlast the associated migrainous headache. FHM is often earlier in onset than typical migraine, frequently beginning in the first or second decade; the frequency of attacks tends to decrease with age. Approximately 40%-50% of families with CACNA1A-FHM have cerebellar signs ranging from nystagmus to progressive, usually late-onset mild ataxia.

Any hypothyroidism, congenital, nongoitrous in which the cause of the disease is a mutation in the THRA gene.

Acute reversible leukoencephalopathy with increased urinary alpha-ketoglutarate (ARLIAK) is an autosomal recessive disorder characterized by acute reversible neurologic deterioration in the context of a febrile illness. The disorder is associated with transient leukoencephalopathy on brain imaging concurrent with the acute episode, as well as persistently increased excretion of dicarboxylic acids, particularly alpha-ketoglutarate (summary by Dewulf et al., 2019).

Neurodevelopmental disorder with impaired language, behavioral abnormalities, and dysmorphic facies (NEDLBF) is characterized by global developmental delay, speech delay, variably impaired intellectual development, behavioral abnormalities, and dysmorphic facial features. The phenotype and severity of the disorder is heterogeneous, ranging from borderline to severe. Brain imaging is usually normal. More variable additional features include early feeding difficulties, failure to thrive, short stature, mild visual impairment, hypotonia, seizures (particularly febrile), and distal skeletal defects of the hands and feet (Jia et al., 2022).