Autosomal Dominant Spinal Muscular Atrophy Research Articles

Non-5q Spinal Muscular Atrophy in a Patient With a Novel BICD2 Missense Variant

Variants in BICD cargo adapter 2 (BICD2) cause autosomal dominant spinal muscular atrophy with lower extremity dominance (SMALED2) which is characterized with lower extremity muscle weakness and atrophy. We describe a novel, heterozygous BICD2 variant (c.1661T>C, [p.Leu554Pro]) in a 21-month-old female patient with a more severe phenotypic presentation than the typical SMALED2 expression including arthrogryposis multiplex congenita, absent deep tendon reflexes, respiratory insufficiency, and cerebral depression. The variant p.Leu554Pro is located just outside of a domain that interacts with the motor protein KIF5A. The detailed neuro-phenotyping and clinical course presented here expand the understanding of BICD2 related disease.

Intrafamilial Variability of the R694C Variant in BICD2 Presenting with Lethal Severe Arthrogryposis

Arthrogryposis multiplex congenita (AMC) is a heterogeneous condition comprising congenital multiple joint contractures, and it is secondary to decreased fetal mobility following environmental/genetic abnormalities. BICD2 pathogenic variants have been associated with autosomal dominant spinal muscular atrophy with lower extremity predominance (SMALED2). We report the case of a newborn with decreased fetal movements and ventriculomegaly diagnosed in utero, born with severe AMC, multiple bone fractures, congenital hip dislocation, and respiratory insufficiency that led to neonatal death. His mother had AMC diagnosis without established etiology. Her phenotype characterization was key to guide the genetic investigation. A BICD 2 heterozygous variant (NM_001003800.1; c.2080C > T; p. [Arg694Cys]) was detected both in the mother and the newborn. This variant had previously been reported in 3 cases, all having de novo severe SMALED-type 2B (MIM#618291) phenotype. This is the first report of this variant (p. [Arg694Cys]) presenting with an inherited, severe, and lethal phenotype associated to intrafamilial variability, suggesting a more complex phenotype-genotype correlation than previously stated.

The history behind ALS type 8: from the first phenotype description to the discovery of VAPB mutation.

Over the past 68 years, the Finkel type late-onset adult autosomal dominant spinal muscular atrophy (SMA) that is allelic with amyotrophic lateral sclerosis-8 (ALS8) gained a genotype-phenotype correlation among the motor neuron diseases through the work of groups led by Zatz and Marques Jr.

A novel BICD2 mutation of a patient with Spinal Muscular Atrophy Lower Extremity Predominant 2.

The bicaudal D homolog 2 (BICD2) gene encodes a protein required for the stable complex of dynein and dynactin, which functions as a motor protein working along the microtubule cytoskeleton. Both inherited and de novo variants of BICD2 are reported with autosomal dominant spinal muscular atrophy with lower extremity predominance (SMALED2). Here, we report a male patient with a novel mutation in the BICD2 gene caused by a heterozygous substitution of arginine with cysteine at residue 162 (Arg162Cys); inherited from his asymptomatic mother. The patient showed typical clinical symptoms of SMALED2, which was genetically confirmed by sequencing. The Arg162Cys mutant clusters with four previously reported variants (c.361C>G, p.Leu121Val; c.581A>G, p.Gln194Arg; c.320C>T, p.Ser107Leu; c.565A>T, p.Ile189Phe) in a region that binds to the dynein-dynactin complex (DDC). The BICD2 domain structures were predicted and the Arg162Cys mutation was localized in the N-terminus coiled-coil segment 1 (CC1) domain. Protein modeling of BICD2's CC1 domain predicted that the Arg162Cys missense variant disrupted interactions with dynein cytoplasmic 1 heavy chain 1 within the DDC. The mutant did this by either changing the electrostatic surface potential or making a broader hydrophobic unit with the neighboring residues. This hereditary case supports the complex and broad genotype-phenotype correlation of BICD2 mutations, which could be explained by incomplete penetrance or variable expressivity in the next generation.

P76-F DYNC1H1 gene mutation in an Estonian family

Background DYNC1H1 gene mutations have been related to many neuromuscular diseases, including autosomal dominant Charcot-Marie-Tooth disease type 2O and autosomal dominant spinal muscular atrophy, with lower extremity predominance (SMA-LED). SMA-LED is a disease with large clinical variability. The early clinical signs are feet deformities, delayed walking and muscle weakness. Material and methods We will present the case report with EMG findings of the family with SMA-LED confirmed by genetic analysis. Results The diagnosis was confirmed with TrueSight One panel covering 4813 genes. Mutation M_001376.4(DYNC1H1):c.1869C > G p.Phe623Leu in DYNC1H1 gene was detected in mother and in two younger children of the family. Conclusion When EMG examination shows neurogenic changes and signs of spinal atrophy, but SMN1 gene test is negative, then it is important to think about rare forms of spinal muscular atrophies.

P.126 - Spinal muscular atrophy with lower extremity predominance: a recognizable phenotype of BICD2 mutations in children

Heterozygous bicaudal D homolog 2 gene (BICD2) mutations cause a form of autosomal dominant spinal muscular atrophy with lower extremity predominance (SMALED). We describe the clinical phenotype, imaging and pathological features in 2 children (a boy and a girl) with BICD2 related SMALED. The first child was born with lower limb arthrogryposis with marked contractures at hips, knees and ankles. She had marked lower limb wasting and weakness with mild scapular winging and weakness in the axial and shoulder muscles. Reflexes were absent in legs. She never achieved independent ambulation and now at the age of 16 years uses a powered chair for mobility. Her course has been non-progressive and complicated by several orthopaedic surgeries in her legs. She does not have any cognitive difficulties. Neurophysiology showed a classic neurogenic pattern. Muscle MRI at the age of 9 showed extensive bilateral and symmetrical fatty degeneration of all muscle groups in the thighs and the calves. She was identified to have a de novo c.565A > T p.(Ile189Phe) heterozygous pathogenic mutation in the BICD2 gene. In the second child, we identified a de novo BICD2 heterozygous variant, c.682G > T, p.Asp288Tyr with lower extremity dominant SMA phenotype. He had congenital foot deformity, muscle atrophy of the legs, and stable weakness mainly of ankle dorsiflexors and invertors. He is independently ambulant. He has brisk reflexes in the legs. There was no apparent sensory or brain dysfunction. A left Quadriceps muscle showed features of a classic neurogenic pattern. Leg muscle MRI showed bilateral atrophy within the vastus lateralis, rectus femoris, sartorius and deep biceps and in the legs, there was atrophy of the gastrocnemius and partial involvement of the tibialis anterior muscles bilaterally. These findings confirm the previously reported recognisable phenotype in children affected with SMALED due to BICD2 mutations. The presence of brisk reflexes in the context of neurogenic changes is of interest and is also observed in other types of SMALED.

Phenotypic extremes of BICD2-opathies: from lethal, congenital muscular atrophy with arthrogryposis to asymptomatic with subclinical features.

Heterozygous variants in BICD cargo adapter 2 (BICD2) cause autosomal dominant spinal muscular atrophy, lower extremity-predominant 2 (SMALED2). The disease is usually characterized by a benign or slowly progressive, congenital or early onset muscle weakness and atrophy that mainly affects the lower extremities, although some affected individuals show involvement of the arms and the shoulder girdle. Here we report unusual extremes of BICD2-related diseases: A severe form of congenital muscular atrophy with arthrogryposis multiplex, respiratory insufficiency and lethality within four months. This was caused by three BICD2 variants, (c.581A>G, p.(Gln194Arg)), (c.1626C>G, p.(Cys542Trp)) and (c.2080C>T, p.(Arg694Cys)), two of which were proven to be de novo. Affected individuals showed reduced fetal movement, weak muscle tone and sparse or no spontaneous activity after birth. Despite assisted ventilation, the condition led to early death. At the other extreme, we identified an asymptomatic woman with a known BICD2 variant (c.2108C>T, p.(Thr703Met)). Radiological examination showed fatty degeneration of selected thigh and calf muscles without clinical consequences. Instead, her son carrying the same variant is affected by a mild childhood onset disease with myopathic and neurogenic features. Mechanisms leading to variable expressivity and onset of BICD2-related disease may include alterations in molecular interactions of BICD2 and suggest the presence of genetic modifiers that may act in a protective fashion to ameliorate or abrogate disease. Our data define an additional severe disease type caused by BICD2 and emphasize a possibly variable etiology of BICD2-opathies with regard to primary muscle and neuronal involvement.

Generational Variance in Phenotypic Expression of Autosomal Dominant Spinal Muscular Atrophy Due to BICD2 Mutation (P4.118)

Generational Variance in Phenotypic Expression of Autosomal Dominant Spinal Muscular Atrophy Due to BICD2 Mutation (P4.118)

Mutations in BICD2, which Encodes a Golgin and Important Motor Adaptor, Cause Congenital Autosomal-Dominant Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a heterogeneous group of neuromuscular disorders caused by degeneration of lower motor neurons. Although functional loss of SMN1 is associated with autosomal-recessive childhood SMA, the genetic cause for most families affected by dominantly inherited SMA is unknown. Here, we identified pathogenic variants in bicaudal D homolog 2 (Drosophila) (BICD2) in three families afflicted with autosomal-dominant SMA. Affected individuals displayed congenital slowly progressive muscle weakness mainly of the lower limbs and congenital contractures. In a large Dutch family, linkage analysis identified a 9q22.3 locus in which exome sequencing uncovered c.320C>T (p.Ser107Leu) in BICD2. Sequencing of 23 additional families affected by dominant SMA led to the identification of pathogenic variants in one family from Canada (c.2108C>T [p.Thr703Met]) and one from the Netherlands (c.563A>C [p.Asn188Thr]). BICD2 is a golgin and motor-adaptor protein involved in Golgi dynamics and vesicular and mRNA transport. Transient transfection of HeLa cells with all three mutant BICD2 cDNAs caused massive Golgi fragmentation. This observation was even more prominent in primary fibroblasts from an individual harboring c.2108C>T (p.Thr703Met) (affecting the C-terminal coiled-coil domain) and slightly less evident in individuals with c.563A>C (p.Asn188Thr) (affecting the N-terminal coiled-coil domain). Furthermore, BICD2 levels were reduced in affected individuals and trapped within the fragmented Golgi. Previous studies have shown that Drosophila mutant BicD causes reduced larvae locomotion by impaired clathrin-mediated synaptic endocytosis in neuromuscular junctions. These data emphasize the relevance of BICD2 in synaptic-vesicle recycling and support the conclusion that BICD2 mutations cause congenital slowly progressive dominant SMA.

Mutations of the LMNA gene can mimic autosomal dominant proximal spinal muscular atrophy

The molecular basis of autosomal dominant spinal muscular atrophy (AD-SMA) is largely unknown. Because the phenotypic spectrum of diseases caused by LMNA mutations is extremely broad and includes myopathies, neuropathies, and cardiomyopathies designated as class 1 laminopathies, we sequenced the LMNA gene in index patients with the clinical picture of proximal SMA, who had a family history suggestive of autosomal dominant inheritance. Among the 19 families investigated, two showed pathogenic mutations of the LMNA gene, resulting in the diagnosis of a class 1 laminopathy in about 10% of our series. We found one novel truncating mutation (c.1477C > T, Q493X) and one previously described missense mutation (c.1130G > T, R377H) in the LMNA gene of two unrelated patients with adult-onset proximal SMA followed by cardiac involvement 14 and 22 years after the onset of weakness. The pedigrees of both families revealed a high frequency of cardiac abnormalities or sudden deaths. Our findings extend the spectrum of laminopathies and are of relevance for genetic counseling and clinical care of families presenting with adult-onset proximal SMA. Particularly, if neurogenic atrophy is combined with a cardiac disease in a family, this should prompt LMNA mutation analysis.

The "split hand" phenomenon: evidence of a spinal origin.

The clinical phenomenon of a split hand, dominant muscle atrophy in the thenar as compared to the hypothenar complex, has been used to support the theory of primary cortical degeneration in amyotrophic lateral sclerosis. However, the same phenomenon, both clinically and electrophysiologically, was observed in three diseases with a second but not first motor neuron affection: autosomal dominant spinal muscular atrophy, spinocerebellar ataxia type 3, and juvenile muscular atrophy. Neurogenic loss in a split hand distribution points to a spinal instead of cortical origin.

Clinical variability of autosomal dominant spinal muscular atrophy

Autosomal dominant spinal muscular atrophy (SMA) is generally classified into a juvenile and an adult onset form. Clinical data of 20 affected members out of 6 families with autosomal dominant proximal SMA are reported. Three families could largely be classified as the adult onset form (onset after 20 years of life). They showed a benign course, most of them remaining ambulatory 10–40 years after clinical onset. Intrafamilial variability of onset was small, the progression of weakness within one family appeared to be very similar. Three patients of the other 3 families suffered from the juvenile onset form (first symptoms before the age of 12 years) with walking difficulties throughout life, whereas other family members would have been classified as adult onset SMA. The latter had an onset between age 17 and 28 years, and were only moderately handicapped when last examined (aged 38–60 years). The great intrafamilial variability in at least some of the families with autosomal dominant SMA is not compatible with the distinction of two clinically defined genetic entities. This observation is important with respect to a reliable prediction in clinical practice and genetic counselling.

Autosomal dominant spinal muscular atrophy: A clinical and genetic study

A clinical and genetic study of 6 kindreds (13 patients) with autosomal dominant spinal muscular atrophy is presented. Evidence is presented to indicate that two separate autosomal dominant genes are involved. One of these causes clinical disease with onset in early childhood (birth-8 years), which is relatively benign and in which proximal selectivity of muscle involvement is not marked. A separate autosomal dominant gene causes a disease with onset in adult life (median age 37 years), showing marked initial proximal selectivity; this disease may be more rapid in its clinical progression. Penetrance of both genes approaches 100%. Incidence figures are presented; less than 2% of all cases of childhood onset spinal muscular atrophy, but 30% of adult onset cases, are due to an autosomal dominant gene transmitted from an affected parent. Implications for prognosis, diagnosis and genetic counselling are discussed. A review of 11 kindreds of dominant spinal muscular atrophy in the literature is presented.