Natural history of NF1 c.2970_2972del p.(Met992del): confirmation of a low risk of complications in a longitudinal study.

Individuals with the three base pair deletion NM_000267.3(NF1):c.2970_2972del p.(Met992del) have been recognised to present with a milder neurofibromatosis type 1 (NF1) phenotype characterised by café-au-lait macules (CALs) and intertriginous freckling, as well as a lack of cutaneous, subcutaneous and plexiform neurofibromas and other NF1-associated complications. Examining large cohorts of patients over time with this specific genotype is important to confirm the presentation and associated risks of this variant across the lifespan. Forty-one individuals with the in-frame NF1 deletion p.Met992del were identified from 31 families. Clinicians completed a standardised clinical questionnaire for each patient and the resulting data were collated and compared to published cohorts. Thirteen patients have been previously reported, and updated clinical information has been obtained for these individuals. Both CALs and intertriginous freckling were present in the majority of individuals (26/41, 63%) and the only confirmed features in 11 (27%). 34/41 (83%) of the cohort met NIH diagnostic criteria. There was a notable absence of all NF1-associated tumour types (neurofibroma and glioma). Neurofibroma were observed in only one individual-a subcutaneous lesion (confirmed histologically). Nineteen individuals were described as having a learning disability (46%). This study confirms that individuals with p.Met992del display a mild tumoural phenotype compared to those with 'classical', clinically diagnosed NF1, and this appears to be the case longitudinally through time as well as at presentation. Learning difficulties, however, appear to affect a significant proportion of NF1 subjects with this phenotype. Knowledge of this genotype-phenotype association is fundamental to accurate prognostication for families and caregivers.

STAC3 variants cause a congenital myopathy with distinctive dysmorphic features and malignant hyperthermia susceptibility.

SH3 and cysteine-rich domain-containing protein 3 (STAC3) is an essential component of the skeletal muscle excitation-contraction coupling (ECC) machinery, though its role and function are not yet completely understood. Here, we report 18 patients carrying a homozygous p.(Trp284Ser) STAC3 variant in addition to a patient compound heterozygous for the p.(Trp284Ser) and a novel splice site change (c.997-1G > T). Clinical severity ranged from prenatal onset with severe features at birth, to a milder and slowly progressive congenital myopathy phenotype. A malignant hyperthermia (MH)-like reaction had occurred in several patients. The functional analysis demonstrated impaired ECC. In particular, KCl-induced membrane depolarization resulted in significantly reduced sarcoplasmic reticulum Ca2+ release. Co-immunoprecipitation of STAC3 with CaV 1.1 in patients and control muscle samples showed that the protein interaction between STAC3 and CaV 1.1 was not significantly affected by the STAC3 variants. This study demonstrates that STAC3 gene analysis should be included in the diagnostic work up of patients of any ethnicity presenting with congenital myopathy, in particular if a history of MH-like episodes is reported. While the precise pathomechanism remains to be elucidated, our functional characterization of STAC3 variants revealed that defective ECC is not a result of CaV 1.1 sarcolemma mislocalization or impaired STAC3-CaV 1.1 interaction.

Case Report: Congenital Erythroleukemia in a Premature Infant with Dysmorphic Features.

We present a case of pure erythroleukemia, diagnosed at autopsy, in a dysmorphic premature infant who died of multiorgan failure within 24 hours of birth. Dysmorphic features included facial and limb abnormalities with long philtrum, microagnathia, downturned mouth, short neck as well as abnormal and missing nails, missing distal phalanx from the second toe, and overlapping toes. Internal findings included gross hepatomegaly and patchy hemorrhages in the liver, splenomegaly, and cardiomegaly; and subdural, intracerebral, and intraventricular hemorrhages. Histology revealed infiltration of bone marrow, kidney, heart, liver, adrenal, lung, spleen, pancreas, thyroid, testis, thymus, and placenta by pure erythroleukemia. Only 6 cases of congenital erythroleukemia have been previously reported with autopsy findings similar to those of this case. The dysmorphic features, although not fitting any specific syndrome, make this case unique. Congenital erythroleukemia and possible syndromes suggested by the dysmorphic features are discussed.

New insights into genotype-phenotype correlation for GLI3 mutations.

The phenotypic spectrum of GLI3 mutations includes autosomal dominant Greig cephalopolysyndactyly syndrome (GCPS) and Pallister-Hall syndrome (PHS). PHS was first described as a lethal condition associating hypothalamic hamartoma, postaxial or central polydactyly, anal atresia and bifid epiglottis. Typical GCPS combines polysyndactyly of hands and feet and craniofacial features. Genotype-phenotype correlations have been found both for the location and the nature of GLI3 mutations, highlighting the bifunctional nature of GLI3 during development. Here we report on the molecular and clinical study of 76 cases from 55 families with either a GLI3 mutation (49 GCPS and 21 PHS), or a large deletion encompassing the GLI3 gene (6 GCPS cases). Most of mutations are novel and consistent with the previously reported genotype-phenotype correlation. Our results also show a correlation between the location of the mutation and abnormal corpus callosum observed in some patients with GCPS. Fetal PHS observations emphasize on the possible lethality of GLI3 mutations and extend the phenotypic spectrum of malformations such as agnathia and reductional limbs defects. GLI3 expression studied by in situ hybridization during human development confirms its early expression in target tissues.

C5orf42 is the major gene responsible for OFD syndrome type VI.

Oral-facial-digital syndrome type VI (OFD VI) is a recessive ciliopathy defined by two diagnostic criteria: molar tooth sign (MTS) and one or more of the following: (1) tongue hamartoma (s) and/or additional frenula and/or upper lip notch; (2) mesoaxial polydactyly of one or more hands or feet; (3) hypothalamic hamartoma. Because of the MTS, OFD VI belongs to the "Joubert syndrome related disorders". Its genetic aetiology remains largely unknown although mutations in the TMEM216 gene, responsible for Joubert (JBS2) and Meckel-Gruber (MKS2) syndromes, have been reported in two OFD VI patients. To explore the molecular cause(s) of OFD VI syndrome, we used an exome sequencing strategy in six unrelated families followed by Sanger sequencing. We identified a total of 14 novel mutations in the C5orf42 gene in 9/11 families with positive OFD VI diagnostic criteria including a severe fetal case with microphthalmia, cerebellar hypoplasia, corpus callosum agenesis, polydactyly and skeletal dysplasia. C5orf42 mutations have already been reported in Joubert syndrome confirming that OFD VI and JBS are allelic disorders, thus enhancing our knowledge of the complex, highly heterogeneous nature of ciliopathies.

Bardet-Biedl syndrome: a study of the renal and cardiovascular phenotypes in a French cohort.

BACKGROUND AND OBJECTIVES: Bardet-Biedl Syndrome (BBS) is a rare autosomal recessive ciliopathy with a wide spectrum of clinical features including obesity, retinitis pigmentosa, polydactyly, mental retardation, hypogonadism, and renal abnormalities. The molecular genetic profile of BBS is currently being investigated after the recent identification of 14 BBS genes involved in primary cilia-linked disease. This study aims to characterize the renal and cardiovascular presentations and to analyze possible relationships between genotypes and clinical phenotypes. DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS: This clinical study was performed in a national cohort of 33 BBS patients, 22 men and 11 women, all aged >16 years (mean age 26.3 years). RESULTS: Renal abnormalities, including impairment of renal function and signs of chronic interstitial nephropathy of dysplastic nature, were documented in 82% of the patients. Cardiovascular evaluations revealed that this group of young patients had significant cardiovascular risk factors. Hypertension was found in >30% of the patients and hyperlipidemia in >60%, and almost 50% had other metabolic abnormalities. Overt diabetes was present in only 6%. With regard to genotype-phenotype correlation, patients with a mutation in the BBS6, BBS10, or BBS12 gene (10 of 33 patients) had more severe renal disease. CONCLUSIONS: Our study results confirm the frequent occurrence of renal involvement in patients with BBS, underscore the high risk of cardiovascular disease in these patients, and provide new information on a possible genotype-phenotype correlation.

High-throughput sequencing of a 4.1 Mb linkage interval reveals FLVCR2 deletions and mutations in lethal cerebral vasculopathy.

Rare lethal disease gene identification remains a challenging issue, but it is amenable to new techniques in high-throughput sequencing (HTS). Cerebral proliferative glomeruloid vasculopathy (PGV), or Fowler syndrome, is a severe autosomal recessive disorder of brain angiogenesis, resulting in abnormally thickened and aberrant perforating vessels leading to hydranencephaly. In three multiplex consanguineous families, genome-wide SNP analysis identified a locus of 14 Mb on chromosome 14. In addition, 280 consecutive SNPs were identical in two Turkish families unknown to be related, suggesting a founder mutation reducing the interval to 4.1 Mb. To identify the causative gene, we then specifically enriched for this region with sequence capture and performed HTS in a proband of seven families. Due to technical constraints related to the disease, the average coverage was only 7×. Nonetheless, iterative bioinformatic analyses of the sequence data identified mutations and a large deletion in the FLVCR2 gene, encoding a 12 transmembrane domain-containing putative transporter. A striking absence of alpha-smooth muscle actin immunostaining in abnormal vessels in fetal PGV brains, suggests a deficit in pericytes, cells essential for capillary stabilization and remodeling during brain angiogenesis. This is the first lethal disease-causing gene to be identified by comprehensive HTS of an entire linkage interval.

Molecular and in silico analyses of the full-length isoform of usherin identify new pathogenic alleles in Usher type II patients.

The usherin gene (USH2A) has been screened for mutations causing Usher syndrome type II (USH2). Two protein isoforms have been identified: a short isoform of 1,546 amino acids and a more recently recognized isoform extending to 5,202 amino acids. We have screened the full length by genomic sequencing. We confirm that many mutations occur in the exons contributing solely to the longer form. USH2 is an autosomal recessive disorder and, in contrast to previous studies, both mutations were identified in 23 patients and a single mutation in 2 out of 33 patients. A total of 34 distinct mutated alleles were identified, including one complex allele with three variants and another with two. A total of 27 of these are novel, confirming that most mutations in usherin are private. Many of the mutations will lead to prematurely truncated protein but as there are a substantial number of missense variants, we have used in silico analysis to assess their pathogenicity. Evidence that they are disease-causing has been produced by protein alignments and three-dimensional (3D) structural predictions when possible. We have identified a previously unrecognized cysteine rich structural domain, containing 12 dicysteine repeats, and show that three missense mutations result in the loss of one of a pair of the defining cysteine-cysteine pairs.

Metaphyseal chondrodysplasia with cone-shaped epiphyses: a specific form involving the lower limbs.

Three unrelated patients affected by a characteristic metaphyseal chondrodysplasia with cup-shaped metaphyses of the knees are described. Lower femoral and upper tibial cone-shaped epiphyses were embedded in the metaphyses. Main clinical features are short stature, shortening of the lower limbs, limitation of knee extension, and normal hands length. Radiographs of skull, spine, and hands showed no abnormality. This particular appearance of the knees has been seldom described in acquired disease such as repeated injuries, meningococcemia, scurvy, and hypervitaminosis A. Metaphyseal dysplasias with these distinctive radiological findings of the knees are uncommon. Differential diagnosis includes trichoscyphodysplasia and acroscyphodysplasia among others. Two other cases reported by Kozlowski showed the most similarities to our three cases and defined a new form of metaphyseal dysplasia with specific lower limbs involvement and cup-shaped metaphyses.