Trace element risk assessment: essentiality vs. toxicity

Distal-less is the earliest known gene specifically expressed in developing insect limbs; its expression is maintained throughout limb development. The homeodomain transcription factor encoded by Distal-less is required for the elaboration of proximodistal pattern elements in Drosophila limbs and can initiate proximodistal axis formation when expressed ectopically. Distal-less homologs, the Dlx genes, are expressed in developing appendages in at least six phyla, including chordates, consistent with requirements for Dlx function in normal appendage development across the animal kingdom. Recent work implicates the Dlx genes of vertebrates in a variety of other developmental processes ranging from neurogenesis to hematopoiesis. We review what is known about the invertebrate and vertebrate Dll/Dlx genes and their varied roles during development. We propose revising the vertebrate nomenclature to reflect phylogenetic relationships among the Dlx genes.

Developmental functions of the Distal-less/Dlx homeobox genes

The medical care of patients affected by rare disorders depends heavily on experiences garnered from prior cases, including those patients evaluated by the treating physician and those published in the medical literature. The utility of published cases is wholly dependent upon accurate diagnosis of those patients. In our experience, the rate of misdiagnosis in Proteus syndrome (PS) is high. Diagnostic criteria have been published, but these criteria have not been applied consistently and were published after many case reports appeared in the literature. We reviewed 205 cases of individuals reported to have PS in the literature and three of us independently applied the diagnostic criteria to these case reports. Our initial diagnostic congruence was 97.1% (199/205); the discrepancies in six cases were easily resolved. Only 97 (47.3%) of reported cases met the diagnostic criteria for PS; 80 cases (39%) clearly did not meet the criteria; and although 28 cases (13.7%) had features suggestive of PS, there were insufficient clinical data to make a diagnosis. Reported cases that met the PS criteria had a higher incidence of premature death, and other complications (scoliosis, megaspondyly, central nervous system abnormalities, tumors, otolaryngologic complications, pulmonary cystic malformations, dental and ophthalmogic complications) compared to those in the non-Proteus group. The cases that met the criteria were more often male, which has implications for hypotheses regarding the etiology and pathophysiology of PS. We also studied the attributes that led authors to conclude the reported patients had PS when we concluded they did not. We found that two of the diagnostic criteria (disproportionate overgrowth and connective tissue nevi) were often misinterpreted. In PS, the abnormal growth is asymmetric, distorting, relentless, and occurred at a faster rate compared to the rest of the body. Furthermore, PS was associated with irregular and disorganized bone, including hyperostoses, hyperproliferation of osteoid with variable calcification, calcified connective tissue, and elongation of long bones with abnormal thinning. In contrast, non-Proteus cases displayed overgrowth that was asymmetric but grew at a rate similar to the growth found in unaffected areas of the body. Also, the overgrowth in non-Proteus cases was associated with normal or enlarged bones together with ballooning of the overlying soft tissues. Taken together, these data show that (1) PS diagnostic criteria sort individuals with asymmetric overgrowth into distinct groups; (2) individuals with PS were more likely to have serious complications; (3) PS affects more males than females; and 4) the published diagnostic criteria are useful for clinical care and research. This article contains supplementary material, which may be viewed at the American Journal of Medical Genetics website at http://www.interscience.wiley.com/jpages/0148-7299/suppmat/index.html.

https://zenodo.org/record/1229111/files/article.pdf

Reassessment of the Proteus syndrome literature: application of diagnostic criteria to published cases.

The Molar Tooth Sign (MTS) is defined by an abnormally deep interpeduncular fossa; elongated, thick, and mal-oriented superior cerebellar peduncles; and absent or hypoplastic cerebellar vermis that together give the appearance of a "molar tooth" on axial brain MRI through the junction of the midbrain and hindbrain (isthmus region). It was first described in Joubert syndrome (JS) where it is present in the vast majority of patients with this diagnosis. We previously showed that the MTS is a component of several other syndromes, including Dekaban-Arima (DAS), Senior-Loken, and COACH (cerebellar vermis hypoplasia (CVH), oligophrenia, ataxia, coloboma, and hepatic fibrosis). Here we present evidence that the MTS is seen together with polymicrogyria, Varadi-Papp syndrome (Orofaciodigital VI (OFD VI)), and a new syndrome with encephalocele and cortical renal cysts. We also present a new patient with COACH syndrome plus the MTS. We propose that the MTS is found in multiple distinct clinical syndromes that may share common developmental mechanisms. Proper classification of patients with these variants of the MTS will be essential for localization and identification of mutant genes.

https://depts.washington.edu/joubert/docs/publications/MTS-syndromes-Gleeson-AmJMedGen2004.pdf

Molar Tooth Sign of the Midbrain-Hindbrain Junction: Occurrence in Multiple Distinct Syndromes

The Molar Tooth Sign (MTS) is defined by an abnormally deep interpeduncular fossa; elongated, thick, and mal‐oriented superior cerebellar peduncles; and absent or hypoplastic cerebellar vermis that together give the appearance of a “molar tooth” on axial brain MRI through the junction of the midbrain and hindbrain (isthmus region). It was first described in Joubert syndrome (JS) where it is present in the vast majority of patients with this diagnosis. We previously showed that the MTS is a component of several other syndromes, including Dekaban–Arima (DAS), Senior–Löken, and COACH (cerebellar vermis hypoplasia (CVH), oligophrenia, ataxia, coloboma, and hepatic fibrosis). Here we present evidence that the MTS is seen together with polymicrogyria, Váradi–Papp syndrome (Orofaciodigital VI (OFD VI)), and a new syndrome with encephalocele and cortical renal cysts. We also present a new patient with COACH syndrome plus the MTS. We propose that the MTS is found in multiple distinct clinical syndromes that may share common developmental mechanisms. Proper classification of patients with these variants of the MTS will be essential for localization and identification of mutant genes. © 2003 Wiley‐Liss, Inc.

Molar Tooth Sign of the Midbrain-Hindbrain Junction

Langer Giedion syndrome.

The patient was a 1-year-old boy, fifth issue of a third degree consanguinous marriage, of a thirty year old gravida five, para three mother and thirty seven year old father. The pregnancy was full term by dates and was uncomplicated by illness, irradiation or teratogenic drug exposure. The three elder siblings were normal, but the fourth issue was a boy who was born at term and had dysmorphic features with club feet like the patient and died at 3 months of age. There was no history of any major illness during infancy. Motor, language and intellectual milestones were markedly delayed.

/pdf/schinzel-giedion-syndrome-lb4xr7do5d.pdf

Schinzel-Giedion syndrome

MURCS association (Mullerian hypoplasia/aplasia, renal agenesis and cervicothoracic somite dysplasia) is emerging as the second most frequent cause of primary amenorrhoea after Turner syndrome. Seven cases have been described and analysed. All cases had absence of uterus and tubes 85% had cervical spine abnormalities such as vertebral fusion, hypoplasia of vertebrae or butterfly vertebrae and short stature and 28% had renal agenesis or ectopy. The latter finding is in contrast to the reports in world literature where the frequency of renal agenesis is higher. There was no familial incidence in these seven cases lending credence to the belief that the association is essentially sporadic.

MURCS association--a review of 7 cases.

Autosomal translocations are rare in the patients with ovarian dysgenesis. An 18-year-old female who presented with primary amenorrhoea had hypergonadotropic hypogonadism and streak ovaries with hypoplastic uterus. Karyotype analysis revealed a balanced autosomal translocation involving chromosomes 1 and 11. The probable role of autosomal translocations in ovarian dysgenesis has been discussed.

Ovarian dysgenesis with balanced autosomal translocation.

Prenatal diagnosis of cri-du-chat syndrome is described in 2 pregnancies. In Case 1, the mother was a balanced translocation carrier and had 2 previously affected off springs. Prenatal diagnosis by chorion villus sampling and cordocentesis was successful in diagnosing an affected conceptus and the pregnancy was electively terminated. Case 2 was referred for nonimmune foetal hydrops and cordocentesis revealed deletion 5p. This second case was noteworthy for the fact that deletion 5p has not been reported to cause foetal hydrops.

Burjor A. Bharucha

Papers

Langer Giedion syndrome.

Schinzel-Giedion syndrome

MURCS association--a review of 7 cases.

Ovarian dysgenesis with balanced autosomal translocation.

Cri-du-chat syndrome: clinical profile and prenatal diagnosis.