O'Sullivan-McLeod syndrome: Unmasking a rare atypical motor neuron disease.

Atypical motor neuron disease represents a rare heterogeneous group of neurodegenerative disorders with clinical, genetic and neuroimaging features distinct from those of the classic spinal or bulbar-onset amyotrophic lateral sclerosis (ALS). O'Sullivan-McLeod syndrome represents an extremely rare lower motor neuronopathy with early adult-onset distal amyotrophy and weakness in the upper limbs with asymmetrical involvement. To add to the few case series and epidemiological and genetic studies describing this variant syndrome, our team here presents a series of seven unrelated Brazilian patients with O'Sullivan-McLeod syndrome in a detailed review of their clinical, neuroimaging, laboratory and neurophysiological findings. A male-to-female ratio of 2.5 to 1 and a mean age at onset of 34.3years was observed, with a mean time delay of 6.6years between symptom-onset and a definitive diagnosis. A positive family history was observed in one case, yet whole-exome sequencing results were negative. Neuroimaging studies were unremarkable. All cases presented with chronic denervation restricted to cervical myotomes and normal sensory nerve conduction studies. This case series, one of the largest groups of patients with O'Sullivan-McLeod syndrome reported in the literature, confirms the sporadic nature of the condition and the difficulties faced in arriving at a definite diagnosis, and also expands the age limit in late adult-onset cases.

Neuroacanthocytosis syndromes.

Neuroacanthocytosis (NA) syndromes are a group of genetically defined diseases characterized by the association of red blood cell acanthocytosis and progressive degeneration of the basal ganglia. NA syndromes are exceptionally rare with an estimated prevalence of less than 1 to 5 per 1'000'000 inhabitants for each disorder. The core NA syndromes include autosomal recessive chorea-acanthocytosis and X-linked McLeod syndrome which have a Huntington's disease-like phenotype consisting of a choreatic movement disorder, psychiatric manifestations and cognitive decline, and additional multi-system features including myopathy and axonal neuropathy. In addition, cardiomyopathy may occur in McLeod syndrome. Acanthocytes are also found in a proportion of patients with autosomal dominant Huntington's disease-like 2, autosomal recessive pantothenate kinase-associated neurodegeneration and several inherited disorders of lipoprotein metabolism, namely abetalipoproteinemia (Bassen-Kornzweig syndrome) and hypobetalipoproteinemia leading to vitamin E malabsorption. The latter disorders are characterized by a peripheral neuropathy and sensory ataxia due to dorsal column degeneration, but movement disorders and cognitive impairment are not present. NA syndromes are caused by disease-specific genetic mutations. The mechanism by which these mutations cause neurodegeneration is not known. The association of the acanthocytic membrane abnormality with selective degeneration of the basal ganglia, however, suggests a common pathogenetic pathway. Laboratory tests include blood smears to detect acanthocytosis and determination of serum creatine kinase. Cerebral magnetic resonance imaging may demonstrate striatal atrophy. Kell and Kx blood group antigens are reduced or absent in McLeod syndrome. Western blot for chorein demonstrates absence of this protein in red blood cells of chorea-acanthocytosis patients. Specific genetic testing is possible in all NA syndromes. Differential diagnoses include Huntington disease and other causes of progressive hyperkinetic movement disorders. There are no curative therapies for NA syndromes. Regular cardiologic studies and avoidance of transfusion complications are mandatory in McLeod syndrome. The hyperkinetic movement disorder may be treated as in Huntington disease. Other symptoms including psychiatric manifestations should be managed in a symptom-oriented manner. NA syndromes have a relentlessly progressive course usually over two to three decades.

The neuropsychiatry of neuroacanthocytosis syndromes.

The neuroacanthocytoses are a group of disorders characterised by peripheral blood acanthocytes, central nervous system as well as neuromuscular symptoms. These disorders uniformly result in pathology in the basal ganglia, which account for the characteristic motor symptoms such as chorea or dystonia, but may also account for the apparent elevated rates of major mental disorders in these syndromes. Elevated rates of dysexecutive syndromes, obsessive-compulsive disorder, depression and schizophrenia-like psychosis appear to occur in chorea-acanthocytosis, McLeod's syndrome, pantothenate kinase-associated neurodegeneration, and Huntington's disease-like 2. Disruptions to key frontostriatal loops secondary to pathology in the striatum and pallidum appear to predispose individuals to major neuropsychiatric syndromes; however, treatment can be instituted for a number of these manifestations, which lessens the overall burden of disease in neuroacanthocytosis patients and their families.

[Neuroacanthocytosis update].

Neuroacanthocytosis is an inclusive term for a genetically heterogeneous group of disorders characterized by the association of neurological abnormalities with red cell acanthocytosis. In the late 1960s, Levine et al. reported a family with a syndrome of neurological deficits such as choreiform involuntary movements, epileptic seizures, intellectual impairment, and paranoid ideation along with acanthocytosis without any disturbance in either alpha- or beta-lipoproteins nor retinitis pigmentosa. Critchley et al. also reported familial cases with acanthocytosis and neurological disorders without beta-lipoproteinemia. These cases have been classified as the Levine-Critchley syndrome of neuroacanthocytosis. Cases of neuroacanthocytosis have been classified into 2 groups depending on the presence or absence of movement disorders such as chorea. One group comprises the core neuroacanthocytosis syndromes in which neurodegeneration occurs primarily in the basal ganglia, specifically the striatum, causing movement disorders. The core neuroacanthocytosis syndromes mainly comprise of the two diseases, chorea-acanthocytosis and the McLeod syndrome. Huntington's disease-like 2, and pantothenate kinase-associated neurodegeneration (PKAN) are very rare but these diseases can also be included in this group of syndromes. Advances in molecular genetics have enabled us to distinguish between these diseases. Recently, the hypoprebetalipoproteinemia, acanthocytosis, retinitis pigmentosa and pallidal degeneration syndrome (HARP syndrome) has been genetically shown to be an allelic form of PKAN. The second group of neuroacanthocytosis syndromes includes abetalipoproteinemia (Bassen-Kornzweig disease) and hypobetalipoproteinemia that are characterized by the abnormal decay of lipoprotein with the intestinal malabsorption of fat leading to neurological abnormalities and acanthocytosis. In this type of neuroacanthocytosis shows a progressive spinocerebellar ataxia with peripheral neuropathy and retinitis pigmentosa are observed, but movement disorders are not seen.