Clinical characteristics.

Fukuyama congenital muscular dystrophy (FCMD) is characterized by hypotonia, symmetric generalized muscle weakness, and CNS migration disturbances that result in changes consistent with cobblestone (previously type II) lissencephaly with cerebral and cerebellar cortical dysplasia. Mild, typical, and severe phenotypes are recognized. Onset typically occurs in early infancy, with a poor suck, weak cry, and floppiness. Affected individuals have contractures of the hips, knees, and interphalangeal joints. Later features include myopathic facial appearance, pseudohypertrophy of the calves and forearms, motor and speech retardation, intellectual disability, seizures, ophthalmologic abnormalities including visual impairment and retinal dysplasia, and progressive cardiac involvement in individuals older than age ten years. Swallowing disturbance occurs in individuals with severe FCMD and in individuals older than age ten years, leading to recurrent aspiration pneumonia and death.

Diagnosis/testing.

The diagnosis of FCMD is established by clinical findings; elevation of serum creatine kinase concentration; characteristic findings on neuroimaging, electromyography, muscle biopsy; and molecular genetic testing of FKTN, the only gene in which pathogenic variants are known to cause FCMD.

Management.

Treatment of manifestations: Physical therapy and stretching exercises, treatment of orthopedic complications, assistance devices such as long leg braces and wheelchairs, use of noninvasive respiratory aids or tracheostomy, antiepileptic drugs, medical or surgical treatment for gastroesophageal reflux, and gastrostomy when indicated.

Surveillance: Monitoring for respiratory function in individuals with advanced disease and monitoring of myocardial involvement by chest x-ray, ECG, and echocardiography in individuals older than age ten years.

Genetic counseling.

FCMD is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk family members and prenatal diagnosis for pregnancies at increased risk are possible if the pathogenic variants in the family are known.

Clinical Diagnosis

The diagnosis of Fukuyama congenital muscular dystrophy (FCMD) is suspected in individuals with the following findings [Fukuyama et al 1960, Fukuyama et al 1981, Osawa et al 1997, Saito & Kobayashi 2001]:

• Early-infantile onset of hypotonia and weakness with contractures of the hips, knees, and interphalangeal joints (100%)
• Severe developmental delay with motor and speech retardation and intellectual disability in spite of relative preservation of socialization (100%)
• Static course until early childhood, followed by diffuse and extensive muscle wasting (most prominent proximally) and later progression of joint contractures (100%)
• Myopathic facial appearance (100%)
• Pseudohypertrophy of the calves and forearms in late infancy (50%)
• Seizures (febrile or afebrile) (50%)
• Ophthalmologic abnormalities, including visual impairment in 53% (15/28) and retinal abnormalities in 32% (9/28) [Saito & Kobayashi 2001]. Retinal abnormality when present is mild and focal. Retinal dysplasia, a pathologic diagnosis, is based on the finding of rosettes of immature photoreceptors.
• Family history consistent with autosomal recessive inheritance

Neuroimaging. MRI reveals the findings of cobblestone lissencephaly comprising five major abnormalities including:

• Irregular or pebbled brain surface, broad gyri with a thick cortex (pachygyria) in the frontal, parietal, and temporal regions, and sometimes areas of small and irregular gyri that resemble polymicrogyria
• Dilated lateral ventricles
• White matter abnormality with hyperintensity on T₂-weighted images and hypointensity on T₁-weighted images [Kato et al 2000] indicative of delayed myelination [Kato et al 2006, Kato et al 2010] rather than dysmyelination
• Mild brain stem hypoplasia in some
• Cerebellar polymicrogyria and cerebellar cysts (observed on MRI in 23 of 25 individuals with FCMD [Aida et al 1994])

In addition:

• The cortex is typically no more than approximately 1 cm in thickness.
• The opercula are poorly developed, leaving an open Sylvian fissure.

EMG findings are characteristic of muscular dystrophy.

Testing

Serum creatine kinase (CK) concentration

• Age <6 years: 10-60 times higher than normal
• Age ≥7 years: 5-20 times higher than normal
• Bed-ridden individuals: Normal

Muscle biopsy

• Findings are characteristic of muscular dystrophy.
• Immunohistochemical staining using α-dystroglycan antibody reveals selective deficiency of α-dystroglycan on the surface membrane of skeletal muscle [Hayashi et al 2001].

Note: (1) Fukutin antibody for immunohistochemical staining was not available until recently. (2) With the development of molecular genetic testing, muscle biopsy is no longer necessary to establish the diagnosis of FCMD.

Testing Strategy

To confirm/establish the diagnosis in a proband. For individuals who meet clinical criteria, have a high serum creatine kinase concentration, and have characteristic findings on neuroimaging, perform FKTN molecular genetic testing (See Figure 1. Diagnostic algorithm):

Figure 1.

Diagnostic algorithm for FCMD

1.

Perform targeted analysis for the c.*4392_*4393insAB185332.1 founder variant in individuals of Japanese, Korean, and Chinese ancestries.

2.

If only one or no pathogenic variant is identified, perform sequence analysis of the entire gene.

Note: In persons of Korean descent, if only one or no pathogenic variant is identified, consider sequence analysis to detect the Korean founder variant c.647+2084G>T.

Carrier testing for at-risk relatives requires prior identification of the pathogenic variants in the family. Note: Carriers are heterozygotes for this autosomal recessive disorder and are not at risk of developing the disorder.

Prenatal diagnosis and preimplantation genetic diagnosis (PGD) for at-risk pregnancies require prior identification of the pathogenic variants in the family.

Clinical Description

Fukuyama congenital muscular dystrophy (FCMD) is characterized by dystrophic changes in the skeletal muscle and by CNS migration disturbances resulting in cerebral and cerebellar cortical dysplasia. The clinical features are hypotonia, weakness, and psychomotor retardation. Mild, typical, and severe phenotypes are recognized. The phenotypic spectrum ranges from a Walker-Warburg syndrome (WWS)-like phenotype at the severe end [Chang et al 2009] to a limb-girdle muscular dystrophy-like phenotype at the mild end [Akiyama et al 2006, Godfrey et al 2006, Godfrey et al 2007, Puckett et al 2009].

Disease onset typically occurs in early infancy. Initial symptoms include poor suck, mildly weak cry, floppiness, and motor developmental delay. Symmetric generalized muscle weakness and hypotonia are present. Some infants exhibit poor weight gain.

Predominantly proximal hypotonia manifests as hyperextensibility of the shoulders and trunk. Limitation of hip extension, hip abduction, and knee extension is also observed and increases with time. "Puffy" cheeks and pseudohypertrophy of the calves and forearms are evident in late infancy. Muscles are hard with a fibrous texture. Deep tendon reflexes are diminished or absent after early infancy. Facial muscle involvement (myopathic facies) is obvious from age six to 12 months and increases with age [Osawa et al 1997]. Open mouth, prognathism, and macroglossia become more evident in childhood. Swallowing difficulty develops after age six years.

Developmental delay and speech delay occur in all individuals. IQ range is usually 30 to 60. In individuals with mild FCMD, the IQ is more than 35; in individuals with severe FCMD the IQ is less than 30. The maximum development in an individual with typical FCMD often consists of dozens of spoken words, sitting without help, or sliding along the floor on the buttocks. Individuals with mild FCMD may achieve independent walking or standing. Individuals with severe FCMD may lack head control or the ability to sit independently.

Social development of individuals with FCMD is not as severely affected as physical and mental abilities [Saito & Kobayashi 2001]. Children with FCMD tend to be the favorites in their nursery, kindergarten, or primary school. Even severely affected individuals with FCMD show eye contact, recognize family members, and make demands through vocalizations. Autistic features are not observed.

Seizures occur in more than 50% of affected individuals [Osawa et al 1997]. In nearly 80% of children with seizures, the seizures manifest between age one year [Osawa et al 1997] and age three years [Yoshioka & Higuchi 2005], or after age six years.

Ocular abnormalities include refractive error (myopia and hypermetropia) in 40%-53% of individuals. Abnormalities of the retina are seen in 32% of those with more severe FCMD [Chijiiwa et al 1983, Tsutsumi et al 1989, Osawa et al 1997]; however, retinal dysplasia is mild and focal.

In a few individuals with severe FCMD confirmed with molecular genetic testing, severe ocular anomalies included microphthalmia, retinal detachment, retinal hypoplasia, and cataracts [Mishima et al 1985, Hino et al 2001, Saito & Kobayashi 2001]. Of note, the characteristic ocular findings of muscle-eye-brain disease (MEBD) or WWS (e.g., anterior chamber abnormalities, glaucoma) are not present in FCMD. (For more information on the eye findings in these disorders, see Congenital Muscular Dystrophy Overview.)

Slowly progressive cardiac involvement is characteristic of FCMD. Individuals who live more than ten years tend to develop fibrosis of the myocardium, as evidenced by postmortem findings [Miura & Shirasawa 1987, Finsterer et al 2010]. In an evaluation of left ventricular (LV) function using M-mode and Doppler echocardiography in 34 individuals with FCMD, eight of 11 individuals over age 15 years showed decreased LV systolic function [Nakanishi et al 2006].

Swallowing dysfunction is observed in individuals with infantile FCMD (especially severe FCMD) and also in individuals with advanced disease over age ten years. Inability to swallow leads to recurrent aspiration pneumonia and death [Hill et al 2004].

Murakami et al [2012] reported sudden exacerbation of muscle weakness with marked elevation of serum creatine kinase (CK) and urinary myoglobin levels a few days after a febrile episode of viral infection, occasionally leading to death.

Neuropathology. Examination of the brain in FCMD shows changes consistent with cobblestone (previously type II) lissencephaly with cerebral and cerebellar cortical dysplasia caused by a defect in neuronal migration [Takada et al 1987, Nakano et al 1996, Yamamoto et al 1996, Yamamoto et al 1997a, Yamamoto et al 1997b, Yamamoto et al 1997c, Saito et al 2000b]. These changes are similar to but typically less severe than the abnormalities described in MEBD and WWS.

Infantile cases can show extensive areas of pachygyria over the surface of the cerebral hemispheres, a feature that is more prominent over the frontal and especially temporal lobes than the parietal and occipital lobes. A variant of polymicrogyria is frequently noted over the cortical surface of the parieto-occipital lobes (see Polymicrogyria Overview).

Cerebellar cysts, lined with the molecular layer and containing leptomeningeal tissue, were observed beneath the malformed cerebellar cortex or areas of polymicrogyria [Aida 1998]. Although distinctive enough to be diagnostic of cobblestone lissencephaly, these changes do not distinguish between FCMD and MEBD or WWS.

In juvenile and adult cases, the agyric areas are more focal and restricted to the occipital lobes. Lissencephalic or agyric areas of malformed cortex may alternate with regions of polymicrogyria, based on fusion of gyri and excessive migration of glio-mesenchymal tissue extending into the subarachnoid space.

A malformed or flat ventral surface of the medulla caused by secondary hypoplasia associated with a small basis pontis and grooves in the spinal cord was recently observed [Saito & Kobayashi 2001].

In fetal cases, neurons and glia migrate through focal defects in the glia limitans, forming verrucous nodules, the initial manifestations of cortical dysplasia. Thus, the overmigration of CNS parenchyma into subarachnoid spaces is considered an essential pathologic process resulting in cortical dysplasia.

Genotype-Phenotype Correlations

Haplotype analysis. Saito et al [2000a] used microsatellite markers closest to FKTN for haplotype analysis of 56 Japanese families, including 35 families with a typical phenotype, 12 families with a mild phenotype, and nine families with a severe phenotype. In total, 38 of 56 families were homozygous for the ancestral haplotype, including 27 of the 35 families with a typical phenotype:

• The probands with the typical phenotype were able to sit unassisted or to slide on the buttocks. Haplotype analysis revealed that 27 (77%) of 35 individuals with the typical phenotype are homozygous for the ancestral founder haplotype, seven (20%) have the founder haplotype on one chromosome, and one (3%) is a homozygote for another haplotype.
• Of the 12 probands with the mild phenotype, eight could walk and the other four could stand with support. Ten were homozygous for the ancestral founder haplotype and two were heterozygous for the ancestral founder haplotype.
• The nine with the severe phenotype lacked head control or the ability to sit without support; three had progressive hydrocephalus, two required a shunt operation, and seven showed ophthalmologic abnormalities. Eight of the nine were heterozygous for the ancestral founder haplotype and one was homozygous for the ancestral founder haplotype.
• The rate of heterozygosity for the ancestral founder haplotype was significantly higher in those with the severe phenotype than in those with the typical or mild phenotype (p<0.005). Individuals with severe FCMD appeared to be compound heterozygous for the founder variant and another pathogenic variant.

Genotype. Kondo-Iida et al [1999] analyzed FKTN in 107 unrelated affected individuals:

• The vast majority of affected individuals have at least one copy of the same mild FKTN variant, c.*4392_*4393insAB185332.1.
  Individuals homozygous for this insertion show a milder phenotype than do compound heterozygotes who have the insertion in combination with a pathogenic missense or nonsense variant on the other allele. This hypothesis is supported by the fact that fukutin-deficient chimeric mice show a severe phenotype that closely resembles WWS [Takeda et al 2003].
• The severe phenotype, including WWS-like manifestations such as hydrocephalus and microphthalmia, was significantly more common in probands who were compound heterozygotes for a single-nucleotide variant and the founder variant (c.*4392_*4393insAB185332.1) than in probands who were homozygous for the founder variant.

Silan et al [2003] and de Bernabé et al [2003] reported two Turkish infants homozygous for pathogenic nonsense variants with a severe FCMD phenotype resembling WWS who died at age ten days and age four months, respectively. One had the nucleotide change c.454dupT in FKTN, causing a frameshift and a premature termination at codon 158 [Silan et al 2003]; the other was homozygous for a novel c.345_346delGCinsCT substitution [de Bernabé et al 2003].

Godfrey et al [2006], Godfrey et al [2007], and Puckett et al [2009] reported a milder LGMD phenotype in individuals heterozygous for a pathogenic missense variant / frameshift variant and homozygous pathogenic missense variants, respectively (see Genetically Related Disorders).

Chang et al [2009] reported five individuals from five families with a severe phenotype similar to WWS. All five individuals were homozygous for c.1167_1168insA, a founder variant in the Ashkenazi Jewish.

Prevalence

FCMD is second in prevalence only to Duchenne muscular dystrophy (DMD) among all subtypes of childhood progressive muscular dystrophy in Japan. FCMD is seldom reported outside of Japan. In the cohort of 337 cases of progressive muscular dystrophy followed in a pediatric neuromuscular clinic over 23 years (1971-1994), DMD accounted for 50.2% of cases and FCMD for 35.3% of cases [Fukuyama 1997]. Based on data obtained from a nationwide multi-institutional study, the annual incidence of FCMD in Japan is in the range of 1.92 to 3.68 in 100,000 live births [Osawa et al 1997].

Molecular genetic testing confirmed the clinical diagnosis of FCMD in 13 individuals of Korean heritage [Lim et al 2010].

The average occurrence of heterozygous carriers identified in various regions of Japan is one in 188 [Watanabe et al 2005].

In individuals of Korean heritage, one carrier in 935 individuals had the ancestral variant c.*4392_*4393insAB185332.1 in the 3' UTR.

Evaluations Following Initial Diagnosis

To establish the extent of disease in an individual diagnosed with Fukuyama congenital muscular dystrophy (FCMD), the following evaluations are recommended:

• Neurologic evaluation, including EEG and brain MRI
• Developmental assessment including assessment of motor skills, cognition, and speech
• Physical therapy evaluation of joint range of motion
• Ophthalmologic evaluation
• Feeding and swallowing assessment in individuals with lack of head control or lack of the ability to sit without support
• Assessment of caloric intake and nutritional status
• Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

There is no definite treatment for FCMD. Multidisciplinary and appropriate management can prolong survival and improve the quality of life for individuals with FCMD.

Treatment includes the following:

• Physical therapy and stretching exercises to promote mobility and prevent contractures
• Monitoring for orthopedic complications such as foot deformity and scoliosis. When scoliosis is present, spinal fusion can preserve breathing function and improve sitting balance [Takaso et al 2010].
• Use of mechanical assistance such as long leg braces to maintain standing posture and wheelchairs to help mobility
• Use of respiratory aids such as nasal intermittent positive pressure ventilator when indicated
  Note: Noninvasive ventilation is offered, particularly at night, before respiratory distress becomes acute.
• Prompt treatment of acute respiratory tract infections; particularly important, as these infections are the most common cause of hospital admissions and death in people with FCMD
• Antiepileptic drugs (AEDs) when indicated
• Surgical treatment for gastroesophageal reflux when indicated
• Gastrostomy when indicated to assure adequate caloric intake
• Routine therapy of cardiomyopathy

Surveillance

Surveillance includes:

• Monitoring of respiratory function in individuals with advanced FCMD over age ten years. Those who survive beyond age 20 years may require tracheostomy or noninvasive respiratory support.
• Monitoring of myocardial involvement by chest x-ray, ECG, and echocardiography in individuals over age ten years.
• Observation/evaluation of gastrointestinal function by a qualified specialist, using a video-fluoroscopic swallow assessment, upper gastrointestinal tract image and pH monitor for gastroesophageal reflux
• Monitoring for foot deformities and scoliosis

Evaluation of Relatives at Risk

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Taniguchi-Ikeda et al [2011] reported that introduction of antisense oligonucleotides (AONs) targeting the splice acceptor, the predicted exon splicing enhancer, and the intronic splicing enhancer prevented pathogenic exon-trapping by SINE (short interspersed sequence)-VNTR (variable number tandem repeat)-Alu (SVA) retrotransposon in cells of patients with FCMD and model mice, rescuing normal fukutin mRNA expression and protein production. They have discovered in human disease a role for SVA-mediated exon-trapping and demonstrated the promise of splicing modulation therapy as the first radical clinical treatment for FCMD.

Search ClinicalTrials.gov in the US and www.ClinicalTrialsRegister.eu in Europe for information on clinical studies for a wide range of diseases and conditions.

Mode of Inheritance

Fukuyama congenital muscular dystrophy (FCMD) is inherited in an autosomal recessive manner.

Risk to Family Members

Parents of a proband

• The parents of an affected child are obligate heterozygotes and therefore carry one mutated allele.
• Heterozygotes (carriers) are asymptomatic.

Sibs of a proband

• At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
• Once an at-risk sib is known to be unaffected, the risk of his/her being a carrier is 2/3.

Offspring of a proband. Individuals with FCMD do not reproduce.

Other family members of a proband. Each sib of the proband's parents is at a 50% risk of being a carrier.

Carrier (Heterozygote) Detection

Carrier testing for at-risk family members is possible if the pathogenic variants have been identified in the family.

Related Genetic Counseling Issues

Family planning

• The optimal time for determination of genetic risk, clarification of carrier status, and discussion of the availability of prenatal testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are carriers or are at risk of being carriers.

DNA banking is the storage of DNA (typically extracted from white blood cells) for possible future use. Because it is likely that testing methodology and our understanding of genes, allelic variants, and diseases will improve in the future, consideration should be given to banking DNA of affected individuals.

Prenatal Testing and Preimplantation Genetic Diagnosis

Once both pathogenic variants have been identified in an affected family member, prenatal diagnosis for a pregnancy at increased risk [Kondo et al 1996, Saito et al 1998, Saito 2006] and preimplantation genetic diagnosis are possible.

Molecular Genetic Pathogenesis

The discovery of FKTN is important in understanding normal brain development and the pathogenesis of congenital muscular dystrophies. (See Congenital Muscular Dystrophy Overview.)

A major manifestation of FCMD is a defect in cortical development, especially neuronal migration, resulting in cobblestone lissencephaly. Similar pathologic changes in muscle and brain occur in the presence of biallelic variants in other genes involved in this metabolic pathway, including FKRP, LARGE, POMGnT1, POMT1, and POMT2.

Matsumura et al [1993] reported that dystrophin-associated proteins such as alpha-dystroglycan (DAG1) have abnormally low expression in FKTN. DAG1 is a cell surface protein that plays an important role in the assembly of the extracellular matrix in muscle, brain, and peripheral nerves by linking the basal lamina to cytoskeletal proteins. Using PCR, immunohistochemistry, and immunoblotting to analyze samples from individuals with FCMD, Hayashi et al [2001] confirmed a deficiency of fukutin and found marked deficiency of highly glycosylated DAG1 in skeletal and cardiac muscle and reduced amounts of DAG1 in brain tissue. Beta-dystroglycan was normal in all tissues examined. These findings supported the suggestion that fukutin deficiency affects the modification of glycosylation of DAG1, which then cannot localize or function properly and may be degraded or eluted from the extracellular surface membrane of the muscle fiber. Hayashi et al [2001] concluded that this disruption underlies the developmental, structural, and functional damage to muscles in individuals with FCMD. Michele et al [2002] demonstrated in individuals with either MEBD or FCMD that alpha-dystroglycan is expressed at the muscle membrane, but hypoglycosylation directly abolishes binding activity of dystroglycan for the ligands laminin, neurexin, and agrin.

Several other genes including ARX [Kato et al 2004], DCX [Gleeson et al 1998], PAFAH1B1 (known formerly as LIS1) [Caspi et al 2000], RELN [Hong et al 2000], and VLDLR [Boycott et al 2005] are known to disrupt neuronal migration and cause lissencephaly in humans, but the pathogenesis and pathology are very different from the cobblestone lissencephaly group.

Gene structure. Both transcript variants NM_001079802.1 and NM_006731.2 have an open reading frame of 1383 bp. The gene spans more than 100 kb of genomic DNA; NM_001079802.1 has 11 exons and NM_006731.2 has ten exons [Kobayashi et al 1998]. Other alternatively spliced transcript variants have been described; for a detailed summary of gene, transcript, and protein information, see Table A, Gene.

Pathogenic variants. A founder haplotype in the Japanese population accounts for more than 80% of FCMD chromosomes; more than 90% of individuals with FCMD have this ancestral haplotype in at least one of the two chromosomes [Kobayashi et al 1998]. The founder variant c.*4392_*4393insAB185332.1 is a retrotransposon insertion of ~3 kb of tandemly repeated sequences into the 3' untranslated region [Kobayashi et al 1998]. The sequence of inserted DNA fragment was 3,062 bp long and was composed of (TCTCCC)₄₁, 27 copies of a 49-bp sequence, a SINE (short interspersed sequence)-type human retroposon sequence, a polyadenylation signal (AATAAA), and poly (A). Furthermore, a target-site duplication, consisting of a direct repeat of AAGAAAAAAAAAATTGT at both ends, indicated retrotransposal insertion of this 3-kb fragment. Kobayashi et al [1998] stated that FCMD is the first human disease known to be caused by an ancient retrotransposal integration. Colombo et al [2000] calculated that the age of the insertion variant causing FCMD in Japanese persons is approximately 102 generations. The estimated age dates the most recent common ancestor of the pathogenic variant-bearing chromosomes to the time when the Yayoi people started migrating to Japan from the Korean peninsula.

Kondo-Iida et al [1999] analyzed FCMD in 107 unrelated, affected individuals and identified four novel pathogenic variants in five cases: one missense, one nonsense, one L1 insertion, and one 1-bp insertion.

Lim et al [2010] reported a deep intronic variant of intron 5 (c.647+2084G>T) that activates a pseudoexon specific to the Korean population.

Normal gene product. Fukutin is predicted to have 461 amino acids. The predicted protein contains an N-terminal signal sequence which, together with results from transfection experiments, suggested that fukutin is a secreted protein. Kobayashi et al [1998] could not demonstrate fukutin in skeletal muscle using polyclonal or monoclonal antibodies. In transfected COS-7 cells, fukutin colocalized with a Golgi marker as well as showing a granular cytoplasmic distribution, suggesting that fukutin passes through the Golgi before being packaged into secretory vesicles. Unlike other muscular dystrophy-associated proteins, no staining for fukutin was seen at the plasma membrane. Kobayashi et al [1998] suggested that fukutin is located in the extracellular matrix, where it interacts with and reinforces a large complex encompassing the outside and inside of muscle membranes. Alternatively, if fukutin is secreted, it may cause muscular dystrophy by an unknown mechanism.

Abnormal gene product. As the 3' untranslated region affects the stability of mRNA, the 3' UTR insertion (c.*4392_*4393insAB185332.1 may alter the secondary structure and render the mRNA unstable [Kobayashi et al 1998].

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Revision History

• 10 May 2012 (me) Comprehensive update posted live
• 26 January 2006 (me) Review posted to live Web site
• 8 October 2004 (ks) Original submission