Oro-facial-digital syndrome IX with severe microcephaly: a new variant in a genetically isolated population

Bilateral lipomatous hamartoma of the tongue: A case report in a child with oral-facial-digital syndrome type VI

A hamartoma is a benign proliferation of typical mature cells specific to a particular anatomical site. In the oral cavity, they may occur as isolated cases or be associated with genetic syndromes. Oral-facial-digital syndrome type VI is a rare genetic disorder with an estimated incidence of one in 50,000-250,000 newborns. Here, we report a case of a 2-year-old boy diagnosed with oral-facial-digital syndrome type VI who was referred for evaluation of a bilateral and normochromic to slightly pinkish nodule on the lateral surface of the tongue. Clinically, the child presented hypotonia, low visual acuity, absence of oculocephalic reflex, delay in neuropsychomotor development, and polydactyly in the feet. Excisional biopsies of both sides of the tongue were performed using a 1.5 W high-power diode laser (wavelength of 980 nm), and histopathological analysis revealed abundant mature adipocytes predominantly arranged in lobules that mainly surrounded the minor salivary gland parenchyma. The surgical sites healed with no complications and the patient remains under follow-up for 10 months. Due to the limited literature on this syndrome and the frequent presence of tongue hamartomas in children, dentists need to be familiar with them.

Reduced cone photoreceptor function and subtle systemic manifestations in two siblings with loss of SCLT1

BACKGROUND

The sodium channel and clathrin linker 1 gene (SCLT1) has been involved in the pathogenesis of various ciliopathy disorders such as Bardet-Biedl syndrome, orofaciodigital syndrome type IX, and Senior-Løken syndrome. Detailed exams are warranted to outline all clinical features. Here, we present a family with a milder phenotype of SCLT1-related disease.

MATERIAL AND METHODS

Comprehensive eye examination including fundus images, OCT, color vision, visual fields and electroretinography were performed. Affected individuals were assessed by a pediatrician and a medical geneticist for systemic features of ciliopathy. Investigations included echocardiography, abdominal ultrasonography, blood work-up for diabetes, liver and kidney function. Genetic testing included NGS retinal dystrophy panel, segregation analysis and transcriptome sequencing.

RESULTS

Two male children, age 10 and 8 years, were affected with attention deficit hyperactivity disorder (ADHD), obesity and mild photophobia. The ophthalmic exam revealed reduced best-corrected visual acuity (BCVA), strabismus, hyperopia, astigmatism and moderate red-green defects. Milder changes suggesting photoreceptors disease were found on retinal imaging. Electroretinogram confirmed cone photoreceptors dysfunction. Genetic testing revealed a homozygous likely pathogenic, splice-site variant in SCLT1 gene NM_144643.3: c.1439 + 1del in the proband and in the affected brother. The unaffected parents were heterozygous for the SCLT1 variant. Transcriptome sequencing showed retention of intron 16 in the proband.

CONCLUSIONS

In this report, we highlight the importance of further extensive diagnostics in patients with unexplained reduced vision, strabismus, refractive errors and ADHD spectrum disorders. SCLT1-related retinal degeneration is very rare and isolated reduced function of cone photoreceptors has not previously been observed.

Ocular Manifestations of a Novel Proximal 19p13.3 Microdeletion

Microdeletions at 19p13.3 are rarely reported in the medical literature with significant phenotypic variability. Among the reported cases, common clinical manifestations have included developmental delay, facial dysmorphism, and hypotonia. Herein we described a child with a de novo 19p13.3 microdeletion, proximal to the reported cases of 19p13.3 microdeletion/duplication, with ocular manifestations of bilateral ocular colobomata complicated with microphthalmos and cataract, associated with short stature. This case highlights the phenotypic heterogeneity of deletions in the 19p13.3 region.

Fifteen years of research on oral-facial-digital syndromes: from 1 to 16 causal genes

Oral-facial-digital syndromes (OFDS) gather rare genetic disorders characterised by facial, oral and digital abnormalities associated with a wide range of additional features (polycystic kidney disease, cerebral malformations and several others) to delineate a growing list of OFDS subtypes. The most frequent, OFD type I, is caused by a heterozygous mutation in the OFD1 gene encoding a centrosomal protein. The wide clinical heterogeneity of OFDS suggests the involvement of other ciliary genes. For 15 years, we have aimed to identify the molecular bases of OFDS. This effort has been greatly helped by the recent development of whole-exome sequencing (WES). Here, we present all our published and unpublished results for WES in 24 cases with OFDS. We identified causal variants in five new genes (C2CD3, TMEM107, INTU, KIAA0753 and IFT57) and related the clinical spectrum of four genes in other ciliopathies (C5orf42, TMEM138, TMEM231 and WDPCP) to OFDS. Mutations were also detected in two genes previously implicated in OFDS. Functional studies revealed the involvement of centriole elongation, transition zone and intraflagellar transport defects in OFDS, thus characterising three ciliary protein modules: the complex KIAA0753-FOPNL-OFD1, a regulator of centriole elongation; the Meckel-Gruber syndrome module, a major component of the transition zone; and the CPLANE complex necessary for IFT-A assembly. OFDS now appear to be a distinct subgroup of ciliopathies with wide heterogeneity, which makes the initial classification obsolete. A clinical classification restricted to the three frequent/well-delineated subtypes could be proposed, and for patients who do not fit one of these three main subtypes, a further classification could be based on the genotype.

Update on oral-facial-digital syndromes (OFDS)

Oral-facial-digital syndromes (OFDS) represent a heterogeneous group of rare developmental disorders affecting the mouth, the face and the digits. Additional signs may involve brain, kidneys and other organs thus better defining the different clinical subtypes. With the exception of OFD types I and VIII, which are X-linked, the majority of OFDS is transmitted as an autosomal recessive syndrome. A number of genes have already found to be mutated in OFDS and most of the encoded proteins are predicted or proven to be involved in primary cilia/basal body function. Preliminary data indicate a physical interaction among some of those proteins and future studies will clarify whether all OFDS proteins are part of a network functionally connected to cilia. Mutations in some of the genes can also lead to other types of ciliopathies with partially overlapping phenotypes, such as Joubert syndrome (JS) and Meckel syndrome (MKS), supporting the concept that cilia-related diseases might be a continuous spectrum of the same phenotype with different degrees of severity. To date, seven of the described OFDS still await a molecular definition and two unclassified forms need further clinical and molecular validation. Next-generation sequencing (NGS) approaches are expected to shed light on how many OFDS geneticists should consider while evaluating oral-facial-digital cases. Functional studies will establish whether the non-ciliary functions of the transcripts mutated in OFDS might contribute to any of the phenotypic abnormalities observed in OFDS.

Autosomal recessive diseases among the Athabaskans of the southwestern United States: recent advances and implications for the future

Genetic and linguistic data suggest that the Na-Dene, of which the Athabaskans are the largest group, are part of a later immigration into the Americas than the first Amerind immigration. Whether a second and third immigration can be separated seems unlikely but continued cross-Bering Strait exchanges may have masked what was a greater separation in the past. The movement of tribes into Siberia appears to have involved a genetic bottleneck leading to at least one disease allele shared by Eskimo/Aleuts and Navajos and a second possibly shared by the Navajo and a Siberian population, but not the same Siberian population that share deep linguistic affinities with the Navajo. A second bottleneck appears to have occurred with the migration of Athabaskans from Northwest North America to the Southwestern United States along the Rocky Mountains. This bottleneck is reflected in several rare recessive diseases shared by the Navajo and Apache. Finally, the Navajo were captured and imprisoned under conditions which led to severe population loss. This, and the "hiding away" of a small number of Navajos in what is now the Western portion of the reservation, led to a Navajo-specific bottleneck(s) resulting in an increased frequency of several rare recessive diseases among the Navajo. Prejudice against human genetic research is high among the Southwestern Athabaskans but attempts to bridge the gap are now occurring. The involvement of Navajo scientists in this process is especially encouraging.