The clinical phenotype of alpha-mannosidosis varies considerably, with a wide spectrum of clinical findings and broad variability in individual presentation. At least three clinical types have been suggested in untreated individuals: mild (clinically recognized after age ten years, with myopathy, slow progression, and absence of skeletal abnormalities); moderate (clinically recognized before age ten years, with myopathy, slow progression, and presence of skeletal abnormalities); and severe (obvious progression leading to early death from primary central nervous system involvement or infection). Core features of untreated individuals generally include early childhood-onset non-progressive hearing loss, frequent infections due to immunodeficiency, rheumatologic symptoms (especially systemic lupus erythematosus), developmental delay / intellectual disability, low tone, ataxia, spastic paraplegia, psychiatric findings, bone disease (ranging from asymptomatic osteopenia to focal lytic or sclerotic lesions and osteonecrosis), gastrointestinal dysfunction (including diarrhea, swallowing issues / aspiration, and enlarged liver and spleen), poor growth, eye issues (including tapetoretinal degeneration and optic nerve atrophy), cardiac complications in adults, and pulmonary issues (including parenchymal lung disease). However, with the advent of enzyme replacement therapy, the natural history of this condition may change. Long-term velmanase alfa (VA) treatment outcomes are still being elucidated, but may include improvement in hearing, immunologic profile, and quality of life (improved clinical outcomes for muscle strength). Similarly, affected individuals who underwent hematopoietic stem cell transplantation (HSCT) experienced improvement in development (with preservation of previously learned skills), ability to participate in activities of daily living, stabilization or improvement in skeletal abnormalities, and improvement in hearing ability, although expressive speech and hearing deficiencies remained the most significant clinical problems after HSCT.

D-bifunctional protein deficiency is a disorder of peroxisomal fatty acid beta-oxidation. See also peroxisomal acyl-CoA oxidase deficiency (264470), caused by mutation in the ACOX1 gene (609751) on chromosome 17q25. The clinical manifestations of these 2 deficiencies are similar to those of disorders of peroxisomal assembly, including X-linked adrenoleukodystrophy (ALD; 300100), Zellweger cerebrohepatorenal syndrome (see 214100) and neonatal adrenoleukodystrophy (NALD; see 601539) (Watkins et al., 1995). DBP deficiency has been classified into 3 subtypes depending upon the deficient enzyme activity. Type I is a deficiency of both 2-enoyl-CoA hydratase and 3-hydroxyacyl-CoA dehydrogenase; type II is a deficiency of hydratase activity alone; and type III is a deficiency of dehydrogenase activity alone. Virtually all patients with types I, II, and III have a severe phenotype characterized by infantile-onset of hypotonia, seizures, and abnormal facial features, and most die before age 2 years. McMillan et al. (2012) proposed a type IV deficiency on the basis of less severe features; these patients have a phenotype reminiscent of Perrault syndrome (PRLTS1; 233400). Pierce et al. (2010) noted that Perrault syndrome and DBP deficiency overlap clinically and suggested that DBP deficiency may be underdiagnosed.

Hypomyelinating leukodystrophy-3 (HLD3) is an autosomal recessive severe neurologic disorder characterized by early infantile onset of global developmental delay, lack of development, lack of speech acquisition, and peripheral spasticity associated with decreased myelination in the central nervous system (summary by Feinstein et al., 2010). The disorder is phenotypically similar to X-linked Pelizaeus-Merzbacher disease (PMD; 312080), which is caused by mutation in the PLP1 gene (300401). For a general phenotypic description and a discussion of genetic heterogeneity of HLD, see 312080.

2-hydroxyglutaric aciduria is a condition that causes progressive damage to the brain. The major types of this disorder are called D-2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA).\n\nThe main features of D-2-HGA are delayed development, seizures, weak muscle tone (hypotonia), and abnormalities in the largest part of the brain (the cerebrum), which controls many important functions such as muscle movement, speech, vision, thinking, emotion, and memory. Researchers have described two subtypes of D-2-HGA, type I and type II. The two subtypes are distinguished by their genetic cause and pattern of inheritance, although they also have some differences in signs and symptoms. Type II tends to begin earlier and often causes more severe health problems than type I. Type II may also be associated with a weakened and enlarged heart (cardiomyopathy), a feature that is typically not found with type I.\n\nL-2-HGA particularly affects a region of the brain called the cerebellum, which is involved in coordinating movements. As a result, many affected individuals have problems with balance and muscle coordination (ataxia). Additional features of L-2-HGA can include delayed development, seizures, speech difficulties, and an unusually large head (macrocephaly). Typically, signs and symptoms of this disorder begin during infancy or early childhood. The disorder worsens over time, usually leading to severe disability by early adulthood.\n\nCombined D,L-2-HGA causes severe brain abnormalities that become apparent in early infancy. Affected infants have severe seizures, weak muscle tone (hypotonia), and breathing and feeding problems. They usually survive only into infancy or early childhood.

LMNB1-related autosomal dominant leukodystrophy (ADLD) is a slowly progressive disorder of central nervous system white matter characterized by onset of autonomic dysfunction in the fourth to fifth decade, followed by pyramidal and cerebellar abnormalities resulting in spasticity, ataxia, and tremor. Autonomic dysfunction can include bladder dysfunction, constipation, postural hypotension, erectile dysfunction, and (less often) impaired sweating. Pyramidal signs are often more prominent in the lower extremities (e.g., spastic weakness, hypertonia, clonus, brisk deep tendon reflexes, and bilateral Babinski signs). Cerebellar signs typically appear at the same time as the pyramidal signs and include gait ataxia, dysdiadochokinesia, intention tremor, dysmetria, and nystagmus. Many individuals have sensory deficits starting in the lower limbs. Pseudobulbar palsy with dysarthria, dysphagia, and forced crying and laughing may appear in the seventh or eighth decade. Although cognitive function is usually preserved or only mildly impaired early in the disease course, dementia and psychiatric manifestations can occur as late manifestations. Affected individuals may survive for decades after onset.

The overlapping phenotypes of neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD) represent the milder manifestations of the Zellweger syndrome spectrum (ZSS) of peroxisome biogenesis disorders. The clinical course of patients with the NALD and IRD presentation is variable and may include developmental delay, hypotonia, liver dysfunction, sensorineural hearing loss, retinal dystrophy, and visual impairment. Children with the NALD presentation may reach their teens, and those with the IRD presentation may reach adulthood (summary by Waterham and Ebberink, 2012). For a complete phenotypic description and a discussion of genetic heterogeneity of PBD(NALD/IRD), see 601539. Individuals with mutations in the PEX16 gene have cells of complementation group 9 (CG9, equivalent to CGD). For information on the history of PBD complementation groups, see 214100.

Cerebellar ataxia, impaired intellectual development, and dysequilibrium syndrome (CAMRQ) is a genetically heterogeneous disorder characterized by congenital cerebellar ataxia and impaired intellectual development (summary by Gulsuner et al., 2011). For a discussion of genetic heterogeneity of CAMRQ, see CAMRQ1 (224050).

Spastic paraplegia-75 (SPG75) is an autosomal recessive, slowly progressive neurodegenerative disorder characterized by onset of spastic paraplegia and cognitive impairment in childhood (summary by Lossos et al., 2015). For a discussion of genetic heterogeneity of autosomal recessive SPG, see SPG5A (270800).

Developmental and epileptic encephalopathy-51 (DEE51) is an autosomal recessive severe neurodevelopmental disorder characterized by onset of intractable seizures and hypotonia in the first days or weeks of life. Affected individuals have severely delayed psychomotor development and may show abnormal movements. Brain imaging shows nonspecific abnormalities, such as cerebral atrophy, cerebellar atrophy, and delayed myelination. Laboratory studies showed increased lactate, suggesting mitochondrial dysfunction (summary by Ait-El-Mkadem et al., 2017). For a discussion of genetic heterogeneity of DEE, see 308350.

IRF2BPL-related disorder is characterized by mild-to-profound developmental delay (with regression in many individuals), intellectual disability, seizures (generalized tonic-clonic, myoclonic, absence, focal tonic-clonic, complex partial, infantile spasms, and/or atonic seizures), movement disorder (ataxia, dystonia, tremor, and parkinsonism), spasticity, and neurobehavioral/psychiatric manifestations (autism spectrum disorder, autistic features, anxiety, depression, and psychosis). Feeding issues, gastrointestinal dysmotility, and ophthalmologic manifestations are also reported. Brain MRI can show focal or diffuse cortical and/or subcortical atrophy, cerebellar atrophy (particularly of the vermis), brain stem atrophy, and corpus callosum abnormalities including thinning/atrophy or thickening. Onset is highly variable and can be in the first year of life through the sixth decade. In some individuals the course of the disorder is progressive or debilitating.

Developmental and epileptic encephalopathy-69 (DEE69) is an autosomal dominant severe neurodevelopmental encephalopathic disorder characterized by early-onset refractory seizures, hypotonia, and profoundly impaired development often associated with macrocephaly, hyperkinetic movements, and contractures. The disorder can sometimes result in early death. Some patients may have a favorable seizure response to topiramate medication (summary by Helbig et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of DEE, see 308350.

Neurodevelopmental disorder with cerebral atrophy and facial dysmorphism (NEDCAFD) is an autosomal recessive disorder characterized by global developmental delay apparent from birth. Affected individuals have hypotonia with inability to walk and severely impaired intellectual development with absent language. Most patients have variable dysmorphic facial features including prominent eyes, protruding and low-set ears, and thin upper lip. Brain imaging shows cerebral atrophy, corpus callosum hypoplasia, and a simplified gyral pattern (summary by Rasheed et al., 2021).

Hypomyelinating leukodystrophy-21 (HLD21) is an autosomal recessive neurodegenerative disorder characterized by global developmental delay apparent from infancy with loss of motor, speech, and cognitive milestones in the first decades of life. Affected individuals show cerebellar and pyramidal signs, including nystagmus, ataxia, dystonia, and spasticity, resulting in the loss of ambulation. Other more variable features include feeding difficulties, poor overall growth with microcephaly, optic atrophy, and seizures. Brain imaging shows diffuse hypomyelination of the white matter and atrophy of the cerebellum and corpus callosum. The disorder is progressive and may lead to premature death (summary by Dorboz et al., 2018). For a general phenotypic description and a discussion of genetic heterogeneity of HLD, see 312080.

Autosomal recessive spinocerebellar ataxia-29 (SCAR29) is a progressive neurodegenerative disorder characterized by delayed motor development in early infancy followed by difficulty walking due to an ataxic gait or inability to walk, hypotonia, and variably impaired intellectual development. Other features include dysarthria, nystagmus, peripheral spasticity, nystagmus, and visual impairment. Brain imaging typically shows atrophy of the cerebellar vermis, but other abnormalities may also be present. Some patients are wheelchair-bound and/or nonverbal (summary by Sanderson et al., 2021) In a review of the pathogenesis of disorders with prominent dystonia as a feature, Monfrini et al. (2021) classified SCAR29 as belonging to a group of neurologic disorders termed 'HOPS-associated neurologic disorders' (HOPSANDs), which are caused by mutations in genes encoding various components of the autophagic/endolysosomal system, including VPS41.

The spectrum of CSF1R-related disorder ranges from early-onset disease (age <18 years) to late-onset disease (age =18 years). Early-onset disease is associated with hypotonia, delayed acquisition of developmental milestones, and non-neurologic manifestations (such as skeletal abnormalities); both early- and late-onset disease have similar neurodegenerative involvement. Most affected individuals eventually become bedridden with spasticity, rigidity, and loss of the ability to walk. They lose speech and voluntary movement and appear to be generally unaware of their surroundings. The last stage of disease progresses to a vegetative state with presence of primitive reflexes, such as visual and tactile grasp, mouth-opening reflex, and sucking reflex. Death most commonly results from pneumonia or other infections. About 500 individuals with CSF1R-related disorder have been reported to date.

Autosomal dominant spastic paraplegia-9A is a neurologic disorder characterized by onset of slowly progressive spasticity mainly affecting the lower limbs. The age at onset usually ranges from adolescence to adulthood, and patients have gait difficulties, motor neuropathy, and dysarthria. Additional variable features include cerebellar signs, cataract, pes cavus, and urinary urgency (summary by Coutelier et al., 2015). For a general phenotypic description and a discussion of genetic heterogeneity of autosomal dominant spastic paraplegia, see SPG3A (182600).

Autosomal recessive SPG9B is a neurologic disorder characterized by early-onset complex spastic paraplegia. Affected individuals had delayed psychomotor development, intellectual disability, and severe motor impairment. More variable features include dysmorphic facial features, tremor, and urinary incontinence (summary by Coutelier et al., 2015). For a discussion of genetic heterogeneity of autosomal recessive SPG, see SPG5A (270800).

Neurodevelopmental disorder with microcephaly, hypotonia, nystagmus, and seizures (NEDMHS) is an autosomal recessive disorder characterized by global developmental delay and impaired intellectual development apparent from infancy. Affected individuals have hypotonia with poor or absent motor skills, feeding difficulties with poor overall growth, microcephaly, mild dysmorphic features, and early-onset seizures. Additional variable features, such as nystagmus, cortical blindness, and spasticity, may also occur. Patients with this disorder tend to have recurrent respiratory infections, likely due to aspiration, that may lead to death in childhood (Arnadottir et al., 2022).

X-linked intellectual developmental disorder-111 (XLID111) is a neurodevelopmental disorder characterized by different degrees of impaired intellectual development associated with motor, speech, and behavioral impairments (El Chehadeh et al., 2022).

Childhood ataxia with central nervous system hypomyelination / vanishing white matter (CACH/VWM) is characterized by ataxia, spasticity, and variable optic atrophy. The phenotypic range includes a prenatal/congenital form, a subacute infantile form (onset age <1 year), an early childhood-onset form (onset age 1 to <4 years), a late childhood-/juvenile-onset form (onset age 4 to <18 years), and an adult-onset form (onset =18 years). The prenatal/congenital form is characterized by severe encephalopathy. In the later-onset forms initial motor and intellectual development is normal or mildly delayed, followed by neurologic deterioration with a chronic progressive or subacute course. While in childhood-onset forms motor deterioration dominates, in adult-onset forms cognitive decline and personality changes dominate. Chronic progressive decline can be exacerbated by rapid deterioration during febrile illnesses or following head trauma or major surgical procedures, or by acute and extreme fright.

Neurodevelopmental disorder with intracranial hemorrhage, seizures, and spasticity (NEDIHSS) is an autosomal recessive disorder characterized by prenatal or neonatal onset of intracranial hemorrhage, usually with ventriculomegaly and calcifications, resulting in parenchymal brain damage. Some affected individuals have symptoms incompatible with life and die in utero. Those that survive show profound global developmental delay with almost no motor or cognitive skills, hypotonia, spasticity, and seizures. Other features may include facial dysmorphism, retinal vascular abnormalities, and poor overall growth. The pathogenesis of the disease likely results from dysfunction of vascular endothelial cells in the brain (Lecca et al., 2023).