Adult Refsum disease (ARD is associated with elevated plasma phytanic acid levels, late childhood-onset (or later) retinitis pigmentosa, and variable combinations of anosmia, polyneuropathy, deafness, ataxia, and ichthyosis. Onset of symptoms ranges from age seven months to older than age 50 years. Cardiac arrhythmia and heart failure caused by cardiomyopathy are potentially severe health problems that develop later in life.

Congenital pernicious anemia (PA), or intrinsic factor deficiency, is a rare disorder characterized by the lack of gastric intrinsic factor in the presence of normal acid secretion and mucosal cytology and the absence of GIF antibodies that are found in the acquired form of pernicious anemia (170900). See also pernicious anemia due to defect in the receptor for vitamin B12/intrinsic factor (261100).

Brody disease (BROD) is an autosomal recessive skeletal muscle disorder characterized by exercise-induced muscle stiffness and cramps primarily affecting the arms, legs, and eyelids, although more generalized muscle involvement may also occur. Symptom onset is most often in the first decade, but many patients present and are diagnosed later in life. Skeletal muscle biopsy typically shows variation in fiber size, increased internal nuclei, and atrophy of type II muscle fibers. Rare patients have been reported to develop malignant hyperthermia after administration of anesthesia, suggesting that patients with the disorder should be tested. The disorder results from defective relaxation of fast-twitch (type II) skeletal muscle fibers due to defects in calcium homeostasis and reuptake in the muscle fiber (summary by Odermatt et al., 2000 and Molenaar et al., 2020).

A severe form of axonal Charcot-Marie-Tooth disease, a peripheral sensorimotor neuropathy. Onset in the second or third decade has manifestations of ulceration and infection of the feet. Symmetric and distal weakness develops mostly in the legs together with a severe symmetric distal sensory loss. Tendon reflexes are only reduced at ankles and foot deformities including pes cavus or planus and hammer toes, appear in childhood.

Spinal muscular atrophy (SMA) is a hereditary neuromuscular disorder characterized by degeneration of spinal cord motor neurons resulting in muscle weakness. SMALED shows autosomal dominant inheritance with muscle weakness predominantly affecting the proximal lower extremities (Harms et al., 2010). The most common form of SMA (see, e.g., SMA1, 253300) shows autosomal recessive inheritance and is due to mutation in the SMN1 gene (600354) on chromosome 5q. Genetic Heterogeneity of Lower Extremity-Predominant Spinal Muscular Atrophy See also SMALED2A (615290) and SMALED2B (618291), both of which are caused by mutation in the BICD2 gene (609797) on chromosome 9q22. SMALED2A and SMALED2B differ in age at onset and severity, with SMALED2B being more severe.

Charcot-Marie-Tooth disease, dominant intermediate-A (CMTDIA) is an autosomal dominant peripheral neuropathy characterized by onset of symptoms in the first or second decades of life. Affected individuals have difficulty walking with muscle cramps of the lower limbs; the motor symptoms may be worsened by cold. The disorder is slowly progressive, eventually involving all 4 limbs, but patients remain ambulatory. After age 40, patients develop more severe features, including distal muscle weakness and atrophy, pes cavus, areflexia, and distal sensory loss. Electrophysiologic studies yield nerve conduction velocities with 'intermediate' values between demyelinating and axonal neuropathy (see below). One such family has been reported (Rossi et al., 1985).

Spinocerebellar ataxia type 28 (SCA28) is characterized by young-adult onset, very slowly progressive gait and limb ataxia resulting in coordination and balance problems, dysarthria, ptosis, nystagmus, and ophthalmoparesis. In most individuals, SCA28 presents as a loss of coordination of lower limbs (unsteadiness, gait ataxia). Less frequently, ptosis/ophthalmoplegia, dysarthria, or upper-limb incoordination may occur as the initial finding. The course of the disease is slowly progressive without impairment of functional autonomy even decades after onset.

Neuronal intranuclear inclusion disease (NIID) is an autosomal dominant, slowly progressive neurodegenerative disorder characterized by a wide range of clinical manifestations, including pyramidal and extrapyramidal symptoms, cerebellar ataxia, cognitive decline and dementia, peripheral neuropathy, and autonomic dysfunction. The age at onset varies, but most individuals present as adults between about 30 and 70 years of age. Pathologic investigation shows eosinophilic intranuclear inclusions in almost all cell types, including neurons, skin cells, fibroblasts, and skeletal muscle. Brain imaging shows a characteristic leukoencephalopathy with high intensity signals in the corticomedullary junction on diffusion-weighted imaging (DWI), as well as white matter abnormalities in subcortical and brainstem regions. Skin biopsy combined with brain imaging is useful for diagnosis (summary by Sone et al., 2016). The phenotype in some cases is suggestive of Parkinson disease (see 168600) and/or Alzheimer disease (see 104300), consistent with an evolving phenotypic spectrum of adult-onset NIID (summary by Tian et al., 2019).

An autosomal dominant form of amyotrophic lateral sclerosis caused by mutation(s) in the FIG4 gene, encoding polyphosphoinositide phosphatase.

A rare subtype of autosomal dominant Charcot-Marie-Tooth disease type 2 with characteristics of adolescent to adulthood-onset of symmetrical, slowly progressive distal muscle weakness and atrophy (with a predominant weakness of the distal lower limbs) associated with reduced or absent deep tendon reflexes, pes cavus and mild to moderated deep sensory impairment. There is evidence this disease is caused by a heterozygous loss-of-function mutation in the DHTKD1 gene on chromosome 10p14.

An extremely rare, complex type of hereditary spastic paraplegia, with onset in infancy of pronounced leg spasticity (leading to the inability to walk independently), reduced visual acuity due to optic atrophy and distal wasting of the hands and feet due to an axonal demyelinating sensorimotor neuropathy. Caused by mutations in the TFG gene (3q12.2) encoding protein TFG, which is thought to play a role in ER microtubular architecture and function.

CMTRIC is an autosomal recessive peripheral neuropathy characterized by distal sensory impairment predominantly affecting the lower limbs and resulting in walking difficulties due to muscle weakness and atrophy. The upper limbs may also be affected. Electrophysiologic studies and sural nerve biopsy show mixed features of demyelinating and axonal neuropathy. The age at onset and the severity of the disease are variable (summary by Azzedine et al., 2013). For a discussion of genetic heterogeneity of autosomal recessive intermediate CMT, see CMTRIA (608340).

IMD23 is an autosomal recessive primary immunodeficiency syndrome characterized by onset of recurrent infections, usually respiratory or cutaneous, in early childhood. Immune workup usually shows neutropenia, lymphopenia, eosinophilia, and increased serum IgE or IgA. Neutrophil chemotactic defects have also been reported. Infectious agents include bacteria, viruses, and fungi. Many patients develop atopic dermatitis, eczema, and other signs of autoinflammation. Affected individuals may also show developmental delay or cognitive impairment of varying severity (summary by Bjorksten and Lundmark, 1976 and Zhang et al., 2014).

3-Methylglutaconic aciduria type I (MGCA1) is a rare autosomal recessive disorder of leucine catabolism. The metabolic landmark is urinary excretion of 3-methylglutaconic acid (3-MGA) and its derivatives 3-methylglutaric acid (3-MG) and 3-hydroxyisovaleric acid (3-HIVA). Two main presentations have been described: one with onset in childhood associated with the nonspecific finding of psychomotor retardation, and the other with onset in adulthood of a progressive neurodegenerative disorder characterized by ataxia, spasticity, and sometimes dementia; these patients develop white matter lesions in the brain. However, some asymptomatic pediatric patients have been identified by newborn screening and show no developmental abnormalities when reexamined later in childhood (summary by Wortmann et al., 2010). Genetic Heterogeneity and Classification of Methylglutaconic Aciduria Methylglutaconic aciduria is a clinically and genetically heterogeneous disorder. Type II MGCA (MGCA2), also known as Barth syndrome (BTHS; 302060), is caused by mutation in the tafazzin gene (TAZ; 300394) on chromosome Xq28. It is characterized by mitochondrial cardiomyopathy, short stature, skeletal myopathy, and recurrent infections; cognitive development is normal. Type III MGCA (MGCA3; 258501), caused by mutation in the OPA3 gene (606580) on chromosome 19q13, involves optic atrophy, movement disorder, and spastic paraplegia. In types II and III, the elevations of 3-methylglutaconate and 3-methylglutarate in urine are modest. Type IV MGCA (MGCA4; 250951) represents an unclassified group of patients who have severe psychomotor retardation and cerebellar dysgenesis. Type V MGCA (MGCA5; 610198), caused by mutation in the DNAJC19 gene (608977) on chromosome 3q26, is characterized by early-onset dilated cardiomyopathy with conduction defects, nonprogressive cerebellar ataxia, testicular dysgenesis, and growth failure in addition to 3-methylglutaconic aciduria (Chitayat et al., 1992; Davey et al., 2006). Type VI MGCA (MGCA6; 614739), caused by mutation in the SERAC1 gene (614725) on chromosome 6q25, includes deafness, encephalopathy, and a Leigh-like syndrome. Type VII MGCA (MGCA7B, 616271 and MGCA7A, 619835), caused by mutation in the CLPB gene (616254) on chromosome 11q13, includes cataracts, neurologic involvement, and neutropenia. Type VIII MGCA (MGCA8; 617248) is caused by mutation in the HTRA2 gene (606441) on chromosome 2p13. Type IX MGCA (MGCA9; 617698) is caused by mutation in the TIMM50 gene (607381) on chromosome 19q13. Eriguchi et al. (2006) noted that type I MGCA is very rare, with only 13 patients reported in the literature as of 2003. Wortmann et al. (2013) proposed a pathomechanism-based classification for 'inborn errors of metabolism with 3-methylglutaconic aciduria as discriminative feature.'

Axonal Charcot-Marie-Tooth disease type 2CC is an autosomal dominant peripheral neuropathy that predominantly affects the lower limbs, resulting in muscle weakness and atrophy and gait impairment. Other features include distal sensory impairment and less severe involvement of the upper limbs. The age at onset and severity are variable (summary by Rebelo et al., 2016). For a phenotypic description and a discussion of genetic heterogeneity of axonal CMT type 2, see CMT2A (118210).

Alacrima, achalasia, and impaired intellectual development syndrome (AAMR) is an autosomal recessive disorder characterized by onset of these 3 main features at birth or in early infancy. More variable features include hypotonia, gait abnormalities, anisocoria, and visual or hearing deficits. The disorder shows similarity to the triple A syndrome (231550), but patients with AAMR do not have adrenal insufficiency (summary by Koehler et al., 2013). See also 300858 for a phenotypically similar disorder that shows X-linked inheritance.

A very rare complex subtype of hereditary spastic paraplegia that presents in infancy with delayed motor development (crawling, walking) and has characteristics of lower limb spasticity, increased deep tendon reflexes, extensor plantar responses, impaired vibratory sensation at ankles, amyotrophy and borderline intellectual disability. Additional signs may include gait disturbances, Achilles tendon contractures, and scoliosis and cerebellar abnormalities.

CSF1R-related adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) is characterized by executive dysfunction, memory decline, personality changes, motor impairments, and seizures. A frontal lobe syndrome (e.g., loss of judgment, lack of social inhibitors, lack of insight, and motor persistence) usually appears early in the disease course. The mean age of onset is usually in the fourth decade. Affected individuals eventually become bedridden with spasticity and rigidity. The disease course ranges from two to 30 or more years (mean: 8 years).

Autosomal recessive spinocerebellar ataxia-32 (SCAR32) is a neurologic disorder characterized by the onset of gait ataxia in the second or third decades of life. The disorder is slowly progressive. Other classic features include upper limb ataxia, oculomotor signs, dysphagia, and dysarthria. Some patients may have hyper- or hypokinetic movement abnormalities. Brain imaging shows cerebellar atrophy (Rebelo et al., 2021).