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MFN2 Hereditary Motor and Sensory Neuropathy : Synonyms: MFN2 Charcot-Marie-Tooth Neuropathy, MFN2-HMSNZüchner S
GeneReviews® [Internet], 2020
Revue : GeneReviews® [Internet] Titre : MFN2 Hereditary Motor and Sensory Neuropathy : Synonyms: MFN2 Charcot-Marie-Tooth Neuropathy, MFN2-HMSN Type de document : Article Auteurs : Züchner S Année de publication : 14/05/2020 Langues : Anglais (eng) Mots-clés : article de synthèse ; conseil génétique ; corrélation génotype-phénotype ; description de la maladie ; diagnostic ; diagnostic différentiel ; épidémiologie ; étiologie ; gène MFN2 ; génétique moléculaire ; maladie de Charcot-Marie-Tooth ; maladie du système nerveux périphérique ; nosologie ; physiopathologie ; prévalence ; prise en charge thérapeutique Résumé : Initial Posting: February 18, 2005; Last Update: May 14, 2020.
MFN2 hereditary motor and sensory neuropathy (MFN2-HMSN) is a classic axonal peripheral sensorimotor neuropathy, inherited in either an autosomal dominant (AD) manner (~90%) or an autosomal recessive (AR) manner (~10%). MFN2-HMSN is characterized by more severe involvement of the lower extremities than the upper extremities, distal upper-extremity involvement as the neuropathy progresses, more prominent motor deficits than sensory deficits, and normal (>42 m/s) or only slightly decreased nerve conduction velocities (NCVs). Postural tremor is common. Median onset is age 12 years in the AD form and age eight years in the AR form. The prevalence of optic atrophy is approximately 7% in the AD form and approximately 20% in the AR form.
Molecular genetic testing establishes the diagnosis of MFN2-HMSN in 90% of probands with suggestive findings by identifying a heterozygous MFN2 pathogenic variant and in 10% of probands with suggestive findings by identifying biallelic MFN2 pathogenic variants.
Treatment of manifestations: Neuropathy is often managed by a multidisciplinary team that includes a neurologist, a physiatrist, an orthopedic surgeon, and physical and occupational therapists. Symptomatic treatment relies on special shoes and/or ankle/foot orthoses to correct foot drop and aid walking; surgery as needed for severe pes cavus; forearm crutches, canes, wheelchairs as needed for mobility; exercise as tolerated; acetaminophen or nonsteroidal anti-inflammatory agents for musculoskeletal pain; treatment of neuropathic pain with tricyclic antidepressants or drugs such as carbamazepine or gabapentin. Optic atrophy is managed with low vision aids as per a low vision clinic, consultation with community vision services, and career/employment counseling.
Surveillance: Routine evaluation by: a neurologist to assess disease progression; physical therapy to assess gross motor skills including gait and strength; occupational therapy to assess fine motor skills and coping strategies; and ophthalmologist and low vision clinic to assess visual acuity and need for modification of low vision aids, respectively.
Agents/circumstances to avoid: Obesity (which makes ambulation more difficult); medications (e.g., vincristine, isoniazid, nitrofurantoin) known to cause nerve damage; alcohol and malnutrition (which can cause or exacerbate neuropathy).
Approximately 90% of MFN2-HMSN is inherited an autosomal dominant (AD) manner, and approximately 10% is inherited in an autosomal recessive (AR) manner. Semi-dominant inheritance (i.e., an MFN2 pathogenic variant is associated with mild disease in the heterozygous state and more severe disease in the homozygous or compound heterozygous state) has been reported in two families.
AD MFN2-HMSN. Most affected individuals have an affected parent; the proportion of individuals with a de novo MFN2 pathogenic variant is unknown. Each child of an affected individual has a 50% chance of inheriting the MFN2 pathogenic variant.
AR MFN2-HMSN. At conception, each sib of an individual with autosomal recessive MFN2-HMSN has a 25% chance of being affected, a 50% chance of being an asymptomatic heterozygote (i.e., carrier), and a 25% chance of being unaffected and not a carrier.
Once the MFN2 pathogenic variant(s) have been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing for MFN2-HMSN are possible.
Lien associé : Texte complet disponible en accès libre sur Bookshelf GeneReviews® Pubmed / DOI : Pubmed : 20301684
GNE Myopathy : Synonyms: Distal Myopathy with Rimmed Vacuoles (DMRV), Hereditary Inclusion Body Myopathy (HIBM), Inclusion Body Myopathy Type 2 (IBM2), Nonaka Myopathy, Quadriceps-Sparing MyopathyCarrillo N, Malicdan MC, Huizing M
GeneReviews® [Internet], 2020
Revue : GeneReviews® [Internet] Titre : GNE Myopathy : Synonyms: Distal Myopathy with Rimmed Vacuoles (DMRV), Hereditary Inclusion Body Myopathy (HIBM), Inclusion Body Myopathy Type 2 (IBM2), Nonaka Myopathy, Quadriceps-Sparing Myopathy Type de document : Article Auteurs : Carrillo N ; Malicdan MC ; Huizing M Année de publication : 09/04/2020 Langues : Anglais (eng) Mots-clés : article de synthèse ; conseil génétique ; description de la maladie ; diagnostic ; diagnostic différentiel ; épidémiologie ; étiologie ; gène GNE ; génétique moléculaire ; maladie neuromusculaire ; physiopathologie ; prévalence ; prise en charge thérapeutique ; UDP-N-acétylglucosamine-2-épimérase / N-acétylmannosamine kinase (maladie liée à) Résumé : Initial Posting: March 26, 2004; Last Update: April 9, 2020.
GNE myopathy is a slowly progressive muscle disease that typically presents between age 20 and 40 years with bilateral foot drop caused by anterior tibialis weakness. Lower-extremity muscle involvement progresses from the anterior to the posterior compartment of the lower leg, followed by hamstrings, then hip girdle muscles, with relative sparing of the quadriceps. A wheelchair may be needed about ten to 20 years after the onset of manifestations. The upper extremities, which may be affected within five to ten years of disease onset, do not necessarily follow a distal-to-proximal progression. In advanced stages, neck and core muscles can become affected.
The diagnosis of GNE myopathy is suspected in a proband with suggestive clinical findings and muscle histopathology (rimmed vacuoles, no inflammation) and is established by the presence of biallelic pathogenic variants in GNE identified by molecular genetic testing.
Treatment of manifestations: Evaluation and management are often by a multidisciplinary team that includes neuromuscular specialists, physiatrists, and physical and occupational therapists to address issues secondary to muscle weakness, including the use of assistive ambulatory devices (e.g., ankle-foot orthoses, cane, walker, wheelchair, or powerchair). Adaptive devices to support fine motor function and activities of daily living are needed in advanced stages of the disease. Recommended evaluations also include baseline echocardiogram and pulmonary function tests in nonambulatory individuals, with management by pulmonologists as clinically indicated.
Surveillance: Follow up at least annually by neuromuscular specialists, physiatrists, and physical and occupational therapists to evaluate disease progression and address muscle strength, mobility, function, and activities of daily living; by pulmonologists to monitor respiratory muscle function in patients with advanced disease.
Agents/circumstances to avoid: Cautious use of medications/drugs with potential myotoxicity (e.g., colchicine and statins); avoidance of weight-lifting and repetitive activities that cause muscle pain.
GNE myopathy is inherited in an autosomal recessive manner. If both parents are known to be heterozygous for a GNE pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being an unaffected carrier, and a 25% chance of inheriting both normal alleles. When the GNE pathogenic variants have been identified in an affected family member, molecular genetic carrier testing of at-risk relatives, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible.
Lien associé : Texte complet disponible en accès libre sur Bookshelf GeneReviews® Pubmed / DOI : Pubmed : 20301439
Hereditary myopathy with early respiratory failure : Synonyms: HMERF, MFM-Titinopathy, Myofibrillar Myopathy with Early Respiratory FailurePfeffer G, Chinnery PF
GeneReviews® [Internet], 2020
Revue : GeneReviews® [Internet] Titre : Hereditary myopathy with early respiratory failure : Synonyms: HMERF, MFM-Titinopathy, Myofibrillar Myopathy with Early Respiratory Failure Type de document : Article Auteurs : Pfeffer G ; Chinnery PF Année de publication : 19/03/2020 Langues : Anglais (eng) Mots-clés : article de synthèse ; conseil génétique ; description de la maladie ; diagnostic ; diagnostic différentiel ; épidémiologie ; étiologie ; génétique moléculaire ; maladie neuromusculaire ; myopathie à inclusions ; myopathie d'Edström ; prévalence ; prise en charge thérapeutique Résumé : Initial Posting: February 27, 2014; Last Update: March 19, 2020.
Hereditary myopathy with early respiratory failure (HMERF) is a slowly progressive myopathy that typically begins in the third to fifth decades of life. The usual presenting findings are gait disturbance relating to distal leg weakness or nocturnal respiratory symptoms due to respiratory muscle weakness. Weakness eventually generalizes and affects both proximal and distal muscles. Most affected individuals require walking aids within a few years of onset; some progress to wheelchair dependence and require nocturnal noninvasive ventilatory support about ten years after onset. The phenotype varies even among individuals within the same family: some remain ambulant until their 70s whereas others may require ventilator support in their 40s.
The diagnosis of HMERF is established in a proband with typical clinical findings and/or a heterozygous pathogenic variant in the region of TTN that encodes the 119th fibronectin-3 domain of titin on molecular genetic testing.
Treatment of manifestations: Management is supportive. For distal leg weakness, use of ankle-foot orthoses can optimize independent ambulation early in the disease course; later in the disease course other mobility aids (canes, walkers, or wheelchairs) may be required. Noninvasive ventilation with bilevel positive airway pressure (BiPAP) or continuous positive airway pressure (CPAP) may be indicated for nocturnal hypoventilation initially, followed by mechanical ventilatory support as needed. Influenza vaccination, occupational therapy, and social service support are important.
Surveillance: Reassessment of muscle strength and clinical status annually by a neurologist; pulmonary function testing every six to 12 months, or guided by individual findings.
Pregnancy management: Although the onset of symptoms usually occurs after the age of childbearing, a pregnant woman with early manifestations of HMERF or at risk for HMERF should be considered high-risk because of the associated respiratory muscle weakness and the increased physiologic demands of pregnancy. Consultation with a high-risk maternal-fetal medicine specialist is recommended when possible.
HMERF is inherited in an autosomal dominant manner with variable expressivity. Most individuals diagnosed with HMERF have an affected parent; to date, de novo pathogenic variants have not been reported in any individuals with genetically confirmed HMERF. Each child of an individual with HMERF has a 50% chance of inheriting the pathogenic variant. If the pathogenic variant has been identified in an affected family member, predictive testing for at-risk relatives, prenatal testing for pregnancies at increased risk, and preimplantation genetic testing are possible.
Lien associé : Texte complet disponible en accès libre sur Bookshelf GeneReviews® Pubmed / DOI : Pubmed : 24575448Schoser B
GeneReviews® [Internet], 2020
Revue : GeneReviews® [Internet] Titre : Myotonic Dystrophy Type 2 : Synonym: Proximal Myotonic Myopathy (PROMM) Type de document : Article Auteurs : Schoser B Année de publication : 19/03/2020 Langues : Anglais (eng) Mots-clés : article de synthèse ; conseil génétique ; description de la maladie ; diagnostic ; diagnostic différentiel ; dystrophie myotonique ; dystrophie myotonique de type 2 ; épidémiologie ; étiologie ; génétique moléculaire ; maladie neuromusculaire ; prévalence ; prise en charge thérapeutique Résumé : Initial Posting: September 21, 2006; Last Update: March 19, 2020.
Myotonic dystrophy type 2 (DM2) is characterized by myotonia and muscle dysfunction (proximal and axial weakness, myalgia, and stiffness), and less commonly by posterior subcapsular cataracts, cardiac conduction defects, insulin-insensitive type 2 diabetes mellitus, and other endocrine abnormalities. While myotonia (involuntary muscle contraction with delayed relaxation) has been reported during the first decade, onset is typically in the third to fourth decade, most commonly with fluctuating or episodic muscle pain that can be debilitating and proximal and axial weakness of the neck flexors and the hip flexors. Subsequently, weakness occurs in the elbow extensors and finger flexors. Facial weakness and weakness of the ankle dorsiflexors are less common. Myotonia rarely causes severe symptoms. In a subset of individuals, calf hypertrophy in combination with brisk reflexes is notable.
The diagnosis of DM2 is established in a proband by identification of a heterozygous pathogenic expansion of a CCTG repeat within a complex repeat motif, (TG)n(TCTG)n(CCTG)n in CNBP. The number of CCTG repeats in a pathogenic expansion ranges from approximately 75 to more than 11,000, with a mean of approximately 5,000 repeats. The detection rate of a CNBP CCTG expansion is more than 99% with the combination of routine PCR, Southern blot analysis, and the PCR repeat-primed assay.
Treatment of manifestations: Ankle-foot orthoses, wheelchairs, or other assistive devices as needed for weakness; routine physical activity appears to help maintain muscle strength and endurance and to control musculoskeletal pain; medications used with some success in myalgia management include mexilitene, gabapentin, pregabalin, nonsteroidal anti-inflammatory drugs, low-dose thyroid replacement, and tricyclic antidepressants; myotonia rarely requires treatment but mexilitene or lamotrigine may be beneficial in some individuals; removal of cataracts or epiretinal membrane that impair vision; defibrillator placement for those with arrhythmias; hormone substitution therapy for endocrine dysfunction; prokinetic agents may be helpful for gastrointestinal manifestations; cognitive behavioral therapy and modafinil may be helpful for fatigue and daytime sleepiness; vitamin D supplementation for those with deficiency; hearing aids for sensorineural hearing loss.
Prevention of secondary complications: Anesthetic risk may be increased and therefore assessment of cardiac and respiratory function before and after surgery are recommended. Prompt treatment of hypothyroidism and vitamin D deficiency to reduce secondary weakness and myotonia.
Surveillance: Annual evaluation with neurologist, occupational therapist, and physical therapist; annual ophthalmology evaluation for posterior subcapsular cataracts and epiretinal membranes; annual ECG, echocardiogram, and 24-hour Holter monitoring to detect/monitor cardiac conduction defects and cardiomyopathy; cardiac MRI per cardiologist; annual measurement of fasting serum glucose concentration, glycosylated hemoglobin level, thyroid hormone levels, and vitamin D; serum testosterone and FSH per endocrinologist.
Agents/circumstances to avoid: Cholesterol-lowering medications when associated with increased weakness.
DM2 is inherited in an autosomal dominant manner. To date, all individuals whose biological parents have been evaluated with molecular genetic testing have had one parent with a CCTG repeat expansion; de novo pathogenic variants have not been reported. Each child of an individual with a CCTG repeat expansion has a 50% chance of inheriting the expansion. There is no correlation between disease severity and CCTG repeat length. Prenatal testing for pregnancies at increased risk and preimplantation genetic testing are possible once the CCTG repeat expansion has been identified in an affected family member.
Lien associé : Texte complet disponible en accès libre sur Bookshelf GeneReviews® [Internet] Pubmed / DOI : Pubmed : 20301639Rosenberg H, Sambuughin N, Riazi S, et al.
GeneReviews® [Internet], 2020
Revue : GeneReviews® [Internet] Titre : Malignant Hyperthermia Susceptibility : Synonym: Malignant Hyperpyrexia Type de document : Article Auteurs : Rosenberg H ; Sambuughin N ; Riazi S ; Dirksen R Année de publication : 16/01/2020 Langues : Anglais (eng) Mots-clés : article de synthèse ; biopsie musculaire ; conseil génétique ; corrélation génotype-phénotype ; description de la maladie ; diagnostic clinique ; diagnostic différentiel ; diagnostic moléculaire ; dystrophie musculaire de Becker ; dystrophie musculaire de Duchenne ; dystrophie myotonique de type 1 ; dystrophie myotonique de type 2 ; examen clinique ; gène CACNL1A3 ; gène RYR1 ; génétique moléculaire ; grossesse ; hyperthermie maligne ; myopathie à central core ; myopathie à multiminicores ; myotonie congénitale ; paralysie périodique familiale hypokaliémique ; physiopathologie ; prévalence ; prévention des complications ; recommandation ; rhabdomyolyse ; susceptibilité génétique ; syndrome malin des neuroleptiques ; test de contracture ; thyréotoxicose Résumé : Initial Posting: December 19, 2003; Last Update: January 16, 2020.
Malignant hyperthermia susceptibility (MHS) is a pharmacogenetic disorder of skeletal muscle calcium regulation associated with uncontrolled skeletal muscle hypermetabolism. Manifestations of malignant hyperthermia (MH) are precipitated by certain volatile anesthetics (i.e., halothane, isoflurane, sevoflurane, desflurane, enflurane), either alone or in conjunction with a depolarizing muscle relaxant (specifically, succinylcholine). The triggering substances cause uncontrolled release of calcium from the sarcoplasmic reticulum and may promote entry of extracellular calcium into the myoplasm, causing contracture of skeletal muscles, glycogenolysis, and increased cellular metabolism, resulting in production of heat and excess lactate. Affected individuals experience acidosis, hypercapnia, tachycardia, hyperthermia, muscle rigidity, compartment syndrome, rhabdomyolysis with subsequent increase in serum creatine kinase (CK) concentration, hyperkalemia with a risk for cardiac arrhythmia or even cardiac arrest, and myoglobinuria with a risk for renal failure. In nearly all cases, the first manifestations of MH (tachycardia and tachypnea) occur in the operating room; however, MH may also occur in the early postoperative period. There is mounting evidence that some individuals with MHS will also develop MH with exercise and/or on exposure to hot environments. Without proper and prompt treatment with dantrolene sodium, mortality is extremely high.
The diagnosis of MHS is established with in vitro muscle contracture testing by measuring the contracture responses of biopsied muscle samples to halothane and graded concentrations of caffeine. The diagnosis of MHS can also be established by identification of a pathogenic variant in CACNA1S, RYR1, or STAC3 on molecular genetic testing.
Treatment of manifestations: Early diagnosis of an MH episode is essential. Successful treatment of an acute episode of MH includes: discontinuation of potent inhalation agents and succinylcholine; increase in minute ventilation to lower end-tidal CO2; use of MHAUS helpline; administration of dantrolene sodium intravenously; cooling measures if body temperature is >38.5° C; treatment of cardiac arrhythmias if needed (do not use calcium channel blockers); monitoring blood gases, serum concentrations of electrolytes and CK, blood and urine for myoglobin, and coagulation profile; treatment of metabolic abnormalities.
Prevention of primary manifestations: Individuals with MHS should not be exposed to potent volatile agents and succinylcholine. Individuals undergoing general anesthetics that exceed 30 minutes in duration should have their temperature monitored using an electronic temperature probe. Individuals with MHS should carry proper identification as to their susceptibility.
Agents/circumstances to avoid: Avoid potent inhalation anesthetics and succinylcholine. Calcium channel blockers should not be given together with dantrolene due to a potential cardiac depressant effect. Serotonin antagonist (5HT3-antagonist) antiemetics should be used cautiously. Individuals with MHS should avoid extremes of heat, but not restrict athletic activity unless there is a history of overt rhabdomyolysis and/or heat stroke. Strenuous activities at high ambient temperatures should be avoided or performed with caution. In individuals with MH undergoing cardiac bypass surgery, aggressive rewarming should be avoided, as it may be associated with development of clinical signs of MH.
Evaluation of relatives at risk: If the MHS-causative pathogenic variant in the family is known, molecular genetic testing can be used to established increased risk of MH in a heterozygous individual; molecular genetic testing alone cannot be used to identify family members who are not at increased risk for MH due to other possible genetic risk factors. If the pathogenic variant in the family is not known or if an at-risk relative is found to be negative for a familial pathogenic variant, muscle contracture testing can be used to assess susceptibility to MH.
Pregnancy management: If a pregnant woman with MHS requires a non-emergent surgery, a non-triggering anesthetic (local, nerve block, epidural, spinal anesthesia, or a total intravenous general anesthetic) should be administered. Continuous epidural analgesia is highly recommended for labor and delivery. If a cesarean delivery is indicated in a woman who does not have an epidural catheter in place, neuraxial (spinal, epidural, or combined spinal-epidural) anesthesia is recommended (if not otherwise contraindicated). If a general anesthetic is indicated, a total intravenous anesthetic technique should be administered, with an anesthesia machine that has been prepared for an MH-susceptible individual.
Malignant hyperthermia susceptibility (MHS) is an autosomal dominant disorder. Most individuals diagnosed with MHS have a parent with MHS, although the parent may not have experienced an episode of MH. The proportion of individuals with MHS caused by a de novo pathogenic variant is unknown. Each child of an individual with MHS has a 50% chance of inheriting a causative pathogenic variant. Prenatal teesting for a pregnancy at increased risk is possible if there is a known MH pathogenic variant in the family.
Lien associé : Texte complet disponible en accès libre sur Bookshelf GeneReviews® Pubmed / DOI : Pubmed : 20301325Tomé S, Gourdon G
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