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Noonan syndrome is a heterogeneous autosomal dominant disorder caused by mutations in at least eight genes involved in the RAS/MAPK signaling pathway. Recently, RIT1 (Ras-like without CAAX 1) has been shown to be involved in the pathogenesis of some patients. We report a series of 44 patients from 30 pedigrees (including nine multiplex families) with mutations in RIT1. These patients display a typical Noonan gestalt and facial phenotype. Among the probands, 8.7% showed postnatal growth retardation, 90% had congenital heart defects, 36% had hypertrophic cardiomyopathy (a lower incidence compared with previous report), 50% displayed speech delay and 52% had learning difficulties, but only 22% required special education. None had major skin anomalies. One child died perinatally of juvenile myelomonocytic leukemia. Compared with the canonical Noonan phenotype linked to PTPN11 mutations, patients with RIT1 mutations appear to be less severely growth retarded and more frequently affected by cardiomyopathy. Based on our experience, we estimate that RIT1 could be the cause of 5% of Noonan syndrome patients. Because mutations found constitutionally in Noonan syndrome are also found in several tumors in adulthood, we evaluated the potential contribution of RIT1 to leukemogenesis in Noonan syndrome. We screened 192 pediatric cases of acute lymphoblastic leukemias (96 B-ALL and 96 T-ALL) and 110 cases of juvenile myelomonocytic leukemias (JMML), but detected no variation in these tumoral samples, suggesting that Noonan patients with germline RIT1 mutations are not at high risk to developing JMML or ALL, and that RIT1 has at most a marginal role in these sporadic malignancies.

Baraitser-Winter, Fryns-Aftimos and cerebrofrontofacial syndrome types 1 and 3 have recently been associated with heterozygous gain-of-function mutations in one of the two ubiquitous cytoplasmic actin-encoding genes ACTB and ACTG1 that encode β- and γ-actins. We present detailed phenotypic descriptions and neuroimaging on 36 patients analyzed by our group and six cases from the literature with a molecularly proven actinopathy (9 ACTG1 and 33 ACTB). The major clinical anomalies are striking dysmorphic facial features with hypertelorism, broad nose with large tip and prominent root, congenital non-myopathic ptosis, ridged metopic suture and arched eyebrows. Iris or retinal coloboma is present in many cases, as is sensorineural deafness. Cleft lip and palate, hallux duplex, congenital heart defects and renal tract anomalies are seen in some cases. Microcephaly may develop with time. Nearly all patients with ACTG1 mutations, and around 60% of those with ACTB mutations have some degree of pachygyria with anteroposterior severity gradient, rarely lissencephaly or neuronal heterotopia. Reduction of shoulder girdle muscle bulk and progressive joint stiffness is common. Early muscular involvement, occasionally with congenital arthrogryposis, may be present. Progressive, severe dystonia was seen in one family. Intellectual disability and epilepsy are variable in severity and largely correlate with CNS anomalies. One patient developed acute lymphocytic leukemia, and another a cutaneous lymphoma, indicating that actinopathies may be cancer-predisposing disorders. Considering the multifaceted role of actins in cell physiology, we hypothesize that some clinical manifestations may be partially mutation specific. Baraitser-Winter cerebrofrontofacial syndrome is our suggested designation for this clinical entity.

The microphthalmia-associated transcription factor (MITF) is a basic helix-loop-helix leucine zipper transcription factor, which regulates melanocyte development and the biosynthetic melanin pathway. A notable relationship has been described between non-truncating mutations of its basic domain and Tietz syndrome, which is characterized by albinoid-like hypopigmentation of the skin and hair, rather than the patchy depigmentation seen in Waardenburg syndrome, and severe hearing loss. Twelve patients with new or recurrent non-truncating mutations of the MITF basic domain from six families were enrolled in this study. We observed a wide range of phenotypes and some unexpected features. All the patients had blue irides and pigmentation abnormalities that ranged from diffuse hypopigmentation to Waardenburg-like patches. In addition, they showed congenital complete hearing loss, diffuse hypopigmentation of the skin, freckling and ocular abnormalities, more frequently than patients with MITF mutations outside the basic domain. In conclusion, the non-truncating mutations of the basic domain do not always lead to Tietz syndrome but rather to a large range of phenotypes. Sun-exposed freckles are interestingly observed more frequently in Asian populations. This variability argues for the possible interaction with modifier loci.

Mitochondrial DNA (mtDNA) mutations have been implicated in non-syndromic hearing loss either as primary or as predisposing factors. As only a part of the mitochondrial genome is usually explored in deafness, its prevalence is probably under-estimated. Among 1350 families with non-syndromic sensorineural hearing loss collected through a French collaborative network, we selected 29 large families with a clear maternal lineage and screened them for known mtDNA mutations in 12S rRNA, tRNASer(UCN) and tRNALeu(UUR) genes. When no mutation could be identified, a whole mitochondrial genome screening was performed, using a microarray resequencing chip: the MitoChip version 2.0 developed by Affymetrix Inc. Known mtDNA mutations was found in nine of the 29 families, which are described in the article: five with A1555G, two with the T7511C, one with 7472insC and one with A3243G mutation. In the remaining 20 families, the resequencing Mitochip detected 258 mitochondrial homoplasmic variants and 107 potentially heteroplasmic variants. Controls were made by direct sequencing on selected fragments and showed a high sensibility of the MitoChip but a low specificity, especially for heteroplasmic variations. An original analysis on the basis of species conservation, frequency and phylogenetic investigation was performed to select the more probably pathogenic variants. The entire genome analysis allowed us to identify five additional families with a putatively pathogenic mitochondrial variant: T669C, C1537T, G8078A, G12236A and G15077A. These results indicate that the new MitoChip platform is a rapid and valuable tool for identification of new mtDNA mutations in deafness.

In contrast to the numerous well-known microdeletion syndromes, only a few microduplications have been described, and this discrepancy may be due in part to methodological bias. In order to facilitate the detection of genomic microdeletions and microduplications, we developed a new assay based on QMPSF (Quantitative Multiplex PCR of Short fluorescent Fragments) able to explore simultaneously 12 candidate loci involved in mental retardation (MR) and known to be the target of genomic rearrangements. We first screened 153 patients with MR and facial dysmorphism associated with malformations, or growth anomalies, or familial history, with cytogenetically normal chromosomes, and the absence of FRAXA mutation and subtelomeric rearrangements. In this series, we found a 5q35 deletion removing the NSD1 gene in a patient with severe epilepsy, profound MR and, retrospectively, craniofacial features of Sotos syndrome. In a second series, we screened 140 patients with MR and behaviour disturbance who did not fulfil the de Vries criteria for subtelomeric rearrangements and who had a normal karyotype and no detectable FRAXA mutation. We detected a 22q11 deletion in a patient with moderate MR, obesity, and facial dysmorphism and a 4 Mb 17p11 duplication in a patient with moderate MR, behaviour disturbance, strabismus, and aspecific facial features. This new QMPSF assay can be gradually upgraded to include additional loci involved in newly recognised microduplication/microdeletion syndromes, and should facilitate wide screenings of patients with idiopathic MR and provide better estimates of the microduplication frequency in the MR population.

Sensorineural hearing loss is the most frequent sensory deficit of childhood and is of genetic origin in up to 75% of cases. It has been shown that mutations of the SLC26A4 (PDS) gene were involved in syndromic deafness characterized by congenital sensorineural hearing impairment and goitre (Pendred's syndrome), as well as in congenital isolated deafness (DFNB4). While the prevalence of SLC26A4 mutations in Pendred's syndrome is clearly established, it remains to be studied in large cohorts of patients with nonsyndromic deafness and detailed clinical informations. In this report, 109 patients from 100 unrelated families, aged from 1 to 32 years (median age: 10 years), with nonsyndromic deafness and enlarged vestibular aqueduct, were genotyped for SLC26A4 using DHPLC molecular screening and sequencing. In all, 91 allelic variants were observed in 100 unrelated families, of which 19 have never been reported. The prevalence of SLC26A4 mutations was 40% (40/100), with biallelic mutation in 24% (24/100), while six families were homozygous. All patients included in this series had documented deafness, associated with EVA and without any evidence of syndromic disease. Among patients with SLC26A4 biallelic mutations, deafness was more severe, fluctuated more than in patients with no mutation. In conclusion, the incidence of SLC26A4 mutations is high in patients with isolated deafness and enlarged vestibular aqueduct and could represent up to 4% of nonsyndromic hearing impairment. SLC26A4 could be the second most frequent gene implicated in nonsyndromic deafness after GJB2, in this Caucasian population.

Mutations in GJB2 are the most common cause of congenital nonsyndromic hearing loss. The controversial allele variant M34T has been hypothesized to cause autosomal dominant or recessive nonsyndromic hearing impairment and some in vitro data has been consistent with this hypothesis. In this report, we present the clinical and genotypic study of 11 families (seven familial forms of nonsyndromic sensorineural hearing loss (NSSNHL) and four sporadic cases) in which the M34T GJB2 variant has been identified. The M34T mutation did not segregate with the deafness in six of the seven familial forms of NSSNH. Eight persons with normal audiogram presented a heterozygous M34T variation and five normal hearing individuals were composite heterozygous for M34T and another GJB2 mutation. Four normal hearing individuals with a documented audiogram were M34T/35delG and one was M34T/(GJB6-D13S1830)del. Screening a French control population of 116 subjects we have found an M34T allele frequency of 1.72%. This percentage was not significatively different from the prevalence of the M34T allele in the deaf population, which was 2.12%. All these data suggest that the M34T variant is not clinically significant in human and is a frequent polymorphism in France.