Abstract
LMX1B
haploinsufficiency causes Nail-patella syndrome (NPS; MIM 161200), characterized by nail dysplasia, absent/hypoplastic patellae, chronic kidney disease, and glaucoma. Accordingly in ...mice,
Lmx1b
has been shown to play crucial roles in the development of the limb, kidney and eye. Although one functional allele of
Lmx1b
appears adequate for development,
Lmx1b
null mice display ventral-ventral distal limbs with abnormal kidney, eye and cerebellar development, more disruptive, but fully concordant with NPS. In
Lmx1b
functional knockouts (KOs),
Lmx1b
transcription in the limb is decreased nearly 6-fold, indicating autoregulation. Herein, we report on two conserved
L
mx1b
-
a
ssociated
cis
-
r
egulatory
m
odules (
LARM1
and
LARM2)
that are bound by Lmx1b, amplify
Lmx1b
expression with unique spatial modularity in the limb, and are necessary for Lmx1b-mediated limb dorsalization. These enhancers, being conserved across vertebrates (including coelacanth, but not other fish species), and required for normal locomotion, provide a unique opportunity to study the role of dorsalization in the fin to limb transition. We also report on two NPS patient families with normal
LMX1B
coding sequence, but with loss-of-function variations in the
LARM1/2
region, stressing the role of regulatory modules in disease pathogenesis.
Smith‐Magenis syndrome (SMS), characterized by dysmorphic features, neurodevelopmental disorder, and sleep disturbance, is due to an interstitial deletion of chromosome 17p11.2 (90%) or to point ...mutations in the RAI1 gene. In this retrospective cohort, we studied the clinical, cognitive, and behavioral profile of 47 European patients with SMS caused by a 17p11.2 deletion. We update the clinical and neurobehavioral profile of SMS. Intrauterine growth was normal in most patients. Prenatal anomalies were reported in 15%. 60% of our patients older than 10 years were overweight. Prevalence of heart defects (6.5% tetralogy of Fallot, 6.5% pulmonary stenosis), ophthalmological problems (89%), scoliosis (43%), or deafness (32%) were consistent with previous reports. Epilepsy was uncommon (2%). We identified a high prevalence of obstipation (45%). All patients had learning difficulties and developmental delay, but ID range was wide and 10% of patients had IQ in the normal range. Behavioral problems included temper tantrums and other difficult behaviors (84%) and night‐time awakenings (86%). Optimal care of SMS children is multidisciplinary and requires important parental involvement. In our series, half of patients were able to follow adapted schooling, but 70% of parents had to adapt their working time, illustrating the medical, social, educative, and familial impact of having a child with SMS.
Smith‐Magenis Syndrome (SMS) is a rare disease due to either a small loss in the chromosome 17 or a mutation in a specific gene at the same location. This neurodevelopmental disorder is characterized by learning and intellectual disabilities, behavioral disorder and a specific sleep disturbance with an inversion of the day‐night cycle. Here, we report an important number of SMS patients and thus provide a better support for patients and families.
MicroRNAs (miRNAs) are key regulators of gene expression in animals and plants. Studies in a variety of model organisms show that miRNAs modulate developmental processes. To our knowledge, the only ...hereditary condition known to be caused by a miRNA is a form of adult-onset non-syndromic deafness, and no miRNA mutation has yet been found to be responsible for any developmental defect in humans. Here we report the identification of germline hemizygous deletions of MIR17HG, encoding the miR-17∼92 polycistronic miRNA cluster, in individuals with microcephaly, short stature and digital abnormalities. We demonstrate that haploinsufficiency of miR-17∼92 is responsible for these developmental abnormalities by showing that mice harboring targeted deletion of the miR-17∼92 cluster phenocopy several key features of the affected humans. These findings identify a regulatory function for miR-17∼92 in growth and skeletal development and represent the first example of an miRNA gene responsible for a syndromic developmental defect in humans.
Congenital limb malformations (CLM) comprise many conditions affecting limbs and more than 150 associated genes have been reported. Due to this large heterogeneity, a high proportion of patients ...remains without a molecular diagnosis. In the last two decades, advances in high throughput sequencing have allowed new methodological strategies in clinical practice. Herein, we report the screening of 52 genes/regulatory sequences by multiplex high‐throughput targeted sequencing, in a series of 352 patients affected with various CLM, over a 3‐year period of time. Patients underwent a clinical triage by expert geneticists in CLM. A definitive diagnosis was achieved in 35.2% of patients, the yield varying considerably, depending on the phenotype. We identified 112 single nucleotide variants and 26 copy‐number variations, of which 52 are novel pathogenic or likely pathogenic variants. In 6% of patients, variants of uncertain significance have been found in good candidate genes. We showed that multiplex targeted high‐throughput sequencing works as an efficient and cost‐effective tool in clinical practice for molecular diagnosis of congenital limb malformations. Careful clinical evaluation of patients may maximize the yield of CLM panel testing.
Thrombocytopenia‐absent radius (TAR) syndrome is characterized by radial defect and neonatal thrombocytopenia. It is caused by biallelic variants of RBM8A gene (1q21.1) with the association of a null ...allele and a hypomorphic noncoding variant. RBM8A encodes Y14, a core protein of the exon junction complex involved in messenger RNA maturation. To date, only two hypomorphic variants have been identified. We report on a cohort of 26 patients affected with TAR syndrome and carrying biallelic variants in RBM8A. Half patients carried a 1q21.1 deletion and one of the two known hypomorphic variants. Four novel noncoding variants of RBM8A were identified in the remaining patients. We developed experimental models enabling their functional characterization in vitro. Two variants, located respectively in the 5′‐untranslated region (5′‐UTR) and 3′‐UTR regions, are responsible for a diminished expression whereas two intronic variants alter splicing. Our results bring new insights into the molecular knowledge of TAR syndrome and enabled us to propose genetic counseling for patients' families.
Nail-Patella Syndrome (NPS) is a rare autosomal dominant condition comprising nail and skeletal anomalies. Skeletal features include dysplastic patellae and iliac horns, as well as scapula and elbow ...dysplasia. Nephropathy and glaucoma or intra-ocular hypertension can sometimes be present. NPS is due to variants affecting function in LMX1B, which encodes a LIM-homeodomain protein critical for limb, kidney and eye development. We describe the phenotype and the molecular data of 55 index patients and their 39 relatives presenting with typical NPS. We identified 38 different LMX1B anomalies, 19 of which were not reported before. In our series, 9% of families are not carriers of a LMX1B genomic alteration after extensive study of the coding and non-coding regions of the gene. One of the families showed no linkage to the LMX1B locus, raising the hypothesis of a genetic heterogeneity.
The Loeys-Dietz syndrome is a recently described autosomal dominant aortic-aneurysm syndrome with widespread systemic involvement. The disease is characterized by the triad of arterial tortuosity and ...aneurysms, hypertelorism, and bifid uvula or cleft palate and is caused by heterozygous mutations in the genes encoding transforming growth factor beta receptors 1 and 2 (TGFBR1 and TGFBR2, respectively).
We undertook the clinical and molecular characterization of 52 affected families. Forty probands presented with typical manifestations of the Loeys-Dietz syndrome. In view of the phenotypic overlap between this syndrome and vascular Ehlers-Danlos syndrome, we screened an additional cohort of 40 patients who had vascular Ehlers-Danlos syndrome without the characteristic type III collagen abnormalities or the craniofacial features of the Loeys-Dietz syndrome.
We found a mutation in TGFBR1 or TGFBR2 in all probands with typical Loeys-Dietz syndrome (type I) and in 12 probands presenting with vascular Ehlers-Danlos syndrome (Loeys-Dietz syndrome type II). The natural history of both types was characterized by aggressive arterial aneurysms (mean age at death, 26.0 years) and a high incidence of pregnancy-related complications (in 6 of 12 women). Patients with Loeys-Dietz syndrome type I, as compared with those with type II, underwent cardiovascular surgery earlier (mean age, 16.9 years vs. 26.9 years) and died earlier (22.6 years vs. 31.8 years). There were 59 vascular surgeries in the cohort, with one death during the procedure. This low rate of intraoperative mortality distinguishes the Loeys-Dietz syndrome from vascular Ehlers-Danlos syndrome.
Mutations in either TGFBR1 or TGFBR2 predispose patients to aggressive and widespread vascular disease. The severity of the clinical presentation is predictive of the outcome. Genotyping of patients presenting with symptoms like those of vascular Ehlers-Danlos syndrome may be used to guide therapy, including the use and timing of prophylactic vascular surgery.
Split‐hand/foot malformation (SHFM) is a genetically heterogeneous congenital limb malformation typically limited to a defect of the central rays of the autopod, presenting as a median cleft of hands ...and feet. It can be associated with long bone deficiency or included in more complex syndromes. Among the numerous genetic causes, WNT10B homozygous variants have been recently identified in consanguineous families, but remain still rarely described (SHFM6; MIM225300). We report on three novel SHFM families harboring WNT10B variants and review the literature, allowing us to highlight some clinical findings. The feet are more severely affected than the hands and there is a frequent asymmetry without obvious side‐bias. Syndactyly of third–fourth fingers was a frequent finding (62%). Polydactyly, which was classically described in SHFM6, was only present in 27% of patients. No genotype–phenotype correlation is delineated but heterozygous individuals might have mild features of SHFM, suggesting a dose‐effect of the WNT10B loss‐of‐function.
Nail‐Patella syndrome (NPS) is a genetic disorder generating physical malformations and, in approximately one in three cases, ocular and renal damage. The present research aimed to deeply understand ...patients' subjective experience with NPS, particularly the aspects of the syndrome that affect patients' adaptation and to propose interventions that can improve genetic and psychological counseling and help patients cope with their condition. Semi‐structured interviews of nine people diagnosed with NPS were analyzed using interpretative phenomenological analysis. Results highlighted attempts to look like a person without disabilities by hiding malformations and not telling the truth about symptoms' genetic origin because of patients' poor self‐esteem, negative self‐cognition, and social isolation experienced from childhood to adulthood. Difficulties of adaptation to physical limits and pain were also identified. The majority of participants who were not diagnosed at birth tended to consider physical symptoms as “birth malformations” without imagining other potential implications until receiving a diagnosis. Despite the diagnosis, the majority continued to minimize the potential complications by considering NPS as a “physical difference” and not adhering to medical surveillance.
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