Kleine-Levin Syndrome is a rare neurological disorder with onset typically during adolescence that is characterized by recurrent episodes of hypersomnia, behavioral changes, and cognitive abnormalities, in the absence of structural changes in neuroimaging. As for many functional brain disorders, the exact disease mechanism in Kleine-Levin Syndrome is presently unknown, preventing the development of specific treatment approaches or protective measures. Here we review the pathophysiology and genetics of this functional brain disorder and then present a specific working hypothesis. A neurodevelopmental mechanism has been suspected based on associations with obstetric complications. Recent studies have focused on genetic factors whereby the first genome-wide association study (GWAS) in Kleine-Levin Syndrome has defined a linkage at the TRANK1 locus. A Gene x Environment interaction model involving obstetric complications was proposed based on concepts developed for other functional brain disorders. To stimulate future research, we here performed annotations of the genes under consideration for Kleine-Levin Syndrome in relation to factors expected to be associated with obstetric complications. Annotations used data-mining of gene/protein lists related to for hypoxia, ischemia, and vascular factors and targeted literature searches. Tentative links for TRANK1, four additional genes in the TRANK1 locus, and LMOD3-LMO2 are described. Protein interaction data for TRANK1 indicate links to CBX2, CBX4, and KDM3A, that in turn can be tied to hypoxia. Taken together, the neurological sleep disorder, Kleine-Levin Syndrome, shows genetic and mechanistic overlap with well analyzed brain disorders such as schizophrenia, autism spectrum disorder and ADHD in which polygenic predisposition interacts with external events during brain development, including obstetric complications.

Nemaline myopathy (NEM) type 10, caused by biallelic mutations in LMOD3, is a severe congenital myopathy clinically characterized by generalized hypotonia and muscle weakness, respiratory insufficiency, joint contractures, and bulbar weakness. Here, we describe a family with two adult patients presenting mild nemaline myopathy due to a novel homozygous missense variant in LMOD3. Both patients presented mild delayed motor milestones, frequent falls during infancy, prominent facial weakness and mild muscle weakness in the four limbs. Muscle biopsy showed mild myopathic changes and small nemaline bodies in a few fibers. A neuromuscular gene panel revealed a homozygous missense variant in LMOD3 that co-segregated with the disease in the family (NM_198271.4: c.1030C>T; p.Arg344Trp). The patients described here provide evidence of the phenotype-genotype correlation, suggesting that non-truncating variants in LMOD3 lead to milder phenotypes of NEM type 10.

Kleine-Levin syndrome (KLS) is a rare and debilitating disorder presenting with periodic hypersomnolence, cognitive, psychiatric and behavioral disturbances. In the absence of biomarkers it can be difficult to diagnose. Rare LMOD3 variants in a family and in seven sporadic cases with KLS have been described. Here we report a patient and her family with an unclassified, familial, periodic central disorder of hypersomnolence (CDH) in whom the presence of a LMOD3 gene variant was assessed.
The female patient presented since early adulthood with recurrent episodes of hypersomnolence. Over more than 20 years of follow-up the diagnoses of idiopathic hypersomnia, KLS and hypersomnia associated with a psychiatric condition were made. The family history is positive for periodic hypersomnolence and psychiatric conditions. The patient, her symptomatic mother and her asymptomatic sister carried a Proline for Histidine substitution at codon 552 of the LMOD3-gene. This variant was previously reported in two sporadic KLS patients and its frequency in the general population is below 0.02%.
We report the association of periodic hypersomnia with a polymorphism of the LMOD3-gene in a patient with atypical KLS and a positive family history. Further research is needed to assess the pathological and predictive value of LMOD3 variants in KLS.

Mutations in the Lmod3 gene have been identified as a genetic cause of nemaline myopathy. However, the mechanism underlying this disease and the function of Lmod3 remain largely unknown. In this study, we found that Lmod3 knockdown in C2C12 cells impaired myoblast differentiation, whereas enforced Lmod3 expression enhanced such differentiation. We also discovered that myoblast proliferation was promoted by Lmod3 overexpression but impeded by its knockdown. Additionally, knockdown of Lmod3 led to apoptosis in myoblasts. Concurrently, forced Lmod3 expression in C2C12 cells contributed to activation of the AKT and ERK pathways during myoblast differentiation and proliferation, respectively. Conversely, knockdown of Lmod3 in C2C12 cells produced the opposite results. Furthermore, administration of IGF-1, a booster of both AKT and ERK pathways, partially rescued the inhibitory effect of Lmod3 knockdown on both differentiation and proliferation of C2C12 cells. These results suggest that Lmod3 promotes differentiation and proliferation of myoblasts through the AKT and ERK pathways, respectively.

Fingerprint bodies are observed in a variety of clinical situations with no definite genetic cause identified so far. We report for the first time the association of fingerprint bodies with rods in a patient who developed a slowly progressive myopathy affecting the face and limb extremities. Ultrastructural examination first disclosed fingerprint bodies and on a second biopsy, associated cytoplasmic bodies and rods. Next Generation Sequencing panel of congenital nemaline myopathy genes allowed the identification of two novel variants, a deleterious missense variant (c.1628G>T, p.Arg543Leu) located in the WASP-homology 2 domain, and a deletion (c.366delG, p.Lys122AsnFs*6) in the LMOD3 gene, generally causing severe nemaline myopathy with antenatal onset and early death. Recently, a less severe phenotype similar to our case has been reported. Our study confirms the existence of milder phenotypes linked to LMOD3 mutations and underlines that fingerprint bodies, though not specific, may be an early ultrastructural marker that could be linked, among others, to nemaline myopathy.

Polyhydramnios is sometimes associated with genetic defects. However, establishing an accurate diagnosis and pinpointing the precise genetic cause of polyhydramnios in any given case represents a major challenge because it is known to occur in association with over 200 different conditions. Whole exome sequencing (WES) is now a routine part of the clinical workup, particularly with diseases characterized by atypical manifestations and significant genetic heterogeneity. Here we describe the identification, by means of WES, of novel compound heterozygous truncating variants in the LMOD3 gene [i.e., c.1412delA (p.Lys471Serfs*18) and c.1283dupC (p.Gly429Trpfs*35)] in a Chinese family with two successive fetuses affected with polyhydramnios, thereby potentiating the prenatal diagnosis of nemaline myopathy (NM) in the proband. LMOD3 encodes leiomodin-3, which is localized to the pointed ends of thin filaments and acts as a catalyst of actin nucleation in skeletal and cardiac muscle. This is the first study to describe the prenatal and postnatal manifestations of LMOD3-related NM in the Chinese population. Of all the currently reported NM-causing LMOD3 nonsense and frameshifting variants, c.1412delA generates the shortest truncation at the C-terminal end of the protein, underscoring the critical role of the WH2 domain in LMOD3 structure and function. Survey of the prenatal phenotypes of all known LMOD3-related severe NM cases served to identify fetal edema as a novel presenting feature that may provide an early clue to facilitate prenatal diagnosis of the disease.

We describe the long-term follow-up of a patient with severe nemaline myopathy due to a novel homozygous mutation in the Leiomodin 3 (LMOD3) gene and describe the histopathological characteristics of the disease. The patient presented at birth with hydrops fetalis, multiple joint contractures, severe generalized muscle weakness, no movement, and respiratory insufficiency. At eight years of age, she had bilateral ophthalmoplegia, visual impairment, multiple contractures, and scoliosis, and is dependent on a home mechanical ventilator and gastrostomy. Except for slight head nodding, she has no voluntary movements. Whole-exome sequencing revealed a homozygous one-base duplication in the LMOD3 gene (c.882dupA, p.Asp295Argfs*2), which would result in a truncated protein. Muscle biopsy in the girl and an unrelated patient homozygous for LMOD3 p.Glu357* showed characteristic morphology of the nemaline rods. Many rods appeared as fragments of thickened Z-discs, frequently in pairs, which were interconnected by short thin filaments. Although not specific, this may be a morphological hallmark of LMOD3-associated nemaline myopathy.

To describe the prenatal presentation, including ultrasonographic, histologic, and molecular findings, in 2 fetuses affected with LMOD3-related nemaline myopathy. Prenatal ultrasonographic examinations and histopathologic studies were performed on 2 fetuses with evidence of nemaline myopathy. To establish a molecular diagnosis, whole-exome sequencing was pursued for the affected fetuses. Nemaline myopathy is a common form of congenital myopathy manifesting with nonprogressive generalized muscle weakness, hypotonia, and electron-dense protein inclusions in skeletal myofibers. Although clinically, nemaline myopathy can be viewed as a common pathway phenotype, its molecular basis is heterogeneous, with mutations in 11 identified genes implicated in its pathogenesis so far. Whole-exome sequencing revealed that the affected fetuses were compound heterozygous for 2 newly reported pathogenic variants in the LMOD3 gene, which encodes leiomodin 3. To our knowledge, this article is the first report of LMOD3-related nemaline myopathy since the original reported cohort. We provide a detailed description of the prenatal imaging of these affected fetuses, which we hope, in combination with next-generation sequencing, may contribute to further diagnosis in additional families.

Nemaline myopathy is a rare inherited disorder characterized by weakness, hypotonia, and depressed deep tendon reflexes. It is clinically and genetically heterogeneous, with the most severe phenotype presenting as perinatal akinesia, severe muscle weakness, feeding difficulties and respiratory failure, leading to early mortality. Pathogenic variants in 12 genes, encoding components of the sarcomere or factors related to myogenesis, have been reported in patients affected with the disorder. Here, we describe an early, lethal presentation of decreased fetal movements, hypotonia, muscle weakness, and neonatal respiratory failure requiring ventilator support in three siblings from a consanguineous family. All exhibited perinatal fractures, and thus, a skeletal dysplasia was considered as possibly contributing to the phenotype. However, whole exome sequencing revealed a homozygous, loss-of-function pathogenic variant in LMOD3, which has recently been associated with nemaline myopathy and, in a subset of patients, perinatal fractures. This case demonstrates the importance of considering congenital neuromuscular disorders in the differential diagnosis of perinatal fractures.