Whole-exome sequencing is a valuable diagnostic tool for inherited peripheral neuropathies: Outcomes from a cohort of 50 families.

The inherited peripheral neuropathies (IPNs) are characterized by marked clinical and genetic heterogeneity and include relatively frequent presentations such as Charcot-Marie-Tooth disease and hereditary motor neuropathy, as well as more rare conditions where peripheral neuropathy is associated with additional features. There are over 250 genes known to cause IPN-related disorders but it is estimated that in approximately 50% of affected individuals a molecular diagnosis is not achieved. In this study, we examine the diagnostic utility of whole-exome sequencing (WES) in a cohort of 50 families with 1 or more affected individuals with a molecularly undiagnosed IPN with or without additional features. Pathogenic or likely pathogenic variants in genes known to cause IPN were identified in 24% (12/50) of the families. A further 22% (11/50) of families carried sequence variants in IPN genes in which the significance remains unclear. An additional 12% (6/50) of families had variants in novel IPN candidate genes, 3 of which have been published thus far as novel discoveries (KIF1A, TBCK, and MCM3AP). This study highlights the use of WES in the molecular diagnostic approach of highly heterogeneous disorders, such as IPNs, places it in context of other published neuropathy cohorts, while further highlighting associated benefits for discovery.

Clinical reappraisal of SHORT syndrome with PIK3R1 mutations: toward recommendation for molecular testing and management.

SHORT syndrome has historically been defined by its acronym: short stature (S), hyperextensibility of joints and/or inguinal hernia (H), ocular depression (O), Rieger abnormality (R) and teething delay (T). More recently several research groups have identified PIK3R1 mutations as responsible for SHORT syndrome. Knowledge of the molecular etiology of SHORT syndrome has permitted a reassessment of the clinical phenotype. The detailed phenotypes of 32 individuals with SHORT syndrome and PIK3R1 mutation, including eight newly ascertained individuals, were studied to fully define the syndrome and the indications for PIK3R1 testing. The major features described in the SHORT acronym were not universally seen and only half (52%) had four or more of the classic features. The commonly observed clinical features of SHORT syndrome seen in the cohort included intrauterine growth restriction (IUGR) <10th percentile, postnatal growth restriction, lipoatrophy and the characteristic facial gestalt. Anterior chamber defects and insulin resistance or diabetes were also observed but were not as prevalent. The less specific, or minor features of SHORT syndrome include teething delay, thin wrinkled skin, speech delay, sensorineural deafness, hyperextensibility of joints and inguinal hernia. Given the high risk of diabetes mellitus, regular monitoring of glucose metabolism is warranted. An echocardiogram, ophthalmological and hearing assessments are also recommended.

Lethal acantholytic epidermolysis bullosa due to a novel homozygous deletion in DSP: expanding the phenotype and implications for desmoplakin function in skin and heart.

Desmoplakin is the major linker in desmosomes in epithelia and myocardium, anchoring intermediate filaments by the C-terminus to plakoglobin and plakophilin in the desmosomal plaque. Mutations in the gene DSP encoding desmoplakin have been associated with various phenotypes affecting skin and/or heart. One of these phenotypes, lethal acantholytic epidermolysis bullosa (LAEB), is characterized by extensive postnatal shedding of epidermis leading to early demise and is caused by recessive mutations in the gene DSP resulting in truncation of the desmoplakin C-terminus. Here we describe two infants born to the same consanguinous parents who suffered extensive epidermal dislodgment and died shortly after birth. In addition, universal alopecia, anonychia, malformed ears and cardiomyopathy were observed. As the clinical diagnosis was LAEB, DSP mutation analysis was performed. A homozygous deletion (c.2874del5) abrogating the donor splice site of exon 20 was found. The deletion is predicted to cause read-through in intron 20 with subsequent recognition of a premature termination codon, resulting in desmoplakin lacking its rod domain and C-terminus (p.Lys959MetfsX5). Electron microscopic analysis of skin biopsies showed absence of the desmosomal inner dense plaque and lack of tonofilament insertion. This is the second report of LAEB. These findings suggest DSP mutations as the aetiology of LAEB and cardiomyopathy as part of the phenotype. Furthermore, they indicate that in addition to the desmoplakin C-terminus, the rod domain is dispensable for intrauterine development but is essential for the inner dense plaque of desmosomes.

Cerebrovascular disorders in children with the factor V Leiden mutation.

Since 1995, at least 128 children with a cerebrovascular disorder, cerebral palsy, or both and the factor V Leiden mutation have been reported. The majority of these strokes were in the first year of life, many of them in the perinatal period. Two thirds had an additional exogenous risk factor for thrombosis, and 42% had another recognized endogenous prothrombotic risk factor in combination with the mutation. We review the association of the factor V Leiden mutation and a cerebrovascular disorder in children younger than 16 years of age and describe the clinical features of 8 children with cerebral palsy and the Leiden mutation. This mutation should be considered in the evaluation of children with a stroke or its sequelae, including infants with perinatal stroke.

Congenital abnormalities among children with cerebral palsy: More evidence for prenatal antecedents.

OBJECTIVES: To investigate the association between cerebral palsy (CP) and congenital abnormalities among children with very low, low, and normal birth weight. STUDY DESIGN: A population-based, case-control study among the cohort of 155,636 live births delivered between 1983 and 1985 in 4 California counties. Children with moderate or severe congenital CP (n = 192) diagnosed by age 3 were identified from 2 California State service agencies, and 551 control children were randomly sampled from birth certificate files. Information on congenital abnormalities diagnosed by the age of 1 year was obtained from the California Birth Defects Monitoring Program registry. Odds ratios (OR) and 95% CIs were calculated to estimate risk for CP associated with congenital abnormalities. RESULTS: Among singletons, congenital abnormalities were present in 33 (19.2%) children with CP and 21 (4.3%) control children (OR = 5.2, 95% CI 2.8-9.7). For each birth weight group, the percent of children with congenital abnormalities among children with CP exceeded that among control children. Structural abnormalities of the central nervous system were more common among children with CP (OR = 16.2, 95% CI 5.8-49.3) than control children. In contrast, the percent of children with non-central nervous system abnormalities only was similar between case patients and control subjects. CONCLUSION: These findings provide further evidence that factors operating in the prenatal period contribute significantly to the etiology of CP.

New mesomelic dysplasia with absent fibulae and triangular tibiae.

We report on two unrelated, sporadic cases of a mesomelic dysplasia characterized by absence of fibulae and severely hypoplastic, triangular-shaped tibiae. Moderate mesomelic shortness was present in the upper limbs with proximal widening of the ulnae. There was also axial skeletal involvement in both cases, characterized radiographically by an abnormal pelvis and marked bilateral glenoid hypoplasia. These cases appear to represent a new form of mesomelic dysplasia distinct from those previously delineated.

Exclusion of the branchio-oto-renal syndrome locus (EYA1) from patients with branchio-oculo-facial syndrome.

In addition to craniofacial, auricular, ophthalmologic, and oral anomalies, the distinctive phenotype of the branchio-oculo-facial (BOF) syndrome (MIM 113620) includes skin defects in the neck or infra/supra-auricular region. These unusual areas of thin, erythematous wrinkled skin differ from the discrete cervical pits, cysts, and fistulas of the branchio-oto-renal (BOR) syndrome (MIM 113650). Although the BOF and BOR syndromes are sufficiently distinctive that they should not be confused, both can be associated with nasolacrimal duct stenosis, deafness, prehelical pits, malformed pinna, and renal anomalies. Furthermore, a reported father and son [Legius et al., 1990, Clin Genet 37:347-500] had features of both conditions. It was not clear whether they had an atypical presentation of either BOR or BOF syndrome, or represented a private syndrome. In light of these issues, we selected the BOR locus (EYA1) as a possible gene mutation for the BOF syndrome. In five BOF patients, there were no mutations detected in the EYA1 gene, suggesting that it is not allelic to the BOR syndrome.

Trisomy 12 mosaicism confirmed in multiple organs from a liveborn child.

This patient, in whom trisomy 12 mosaicism was confirmed in multiple organs, is the fifth case diagnosed postnatally and the first reported for whom a meiotic origin of the trisomy, maternal meiosis I, was determined. Mosaic aneuploidy was suspected because of pigmentary dysplasia, a frequent but non-specific finding in chromosomal mosaicism. The severe phenotype of this child, who died in infancy with a complex heart malformation, was probably a result of the high percentage of trisomic cells. Cytogenetic and interphase fluorescent in situ hybridization analyses showed a highly variable distribution of aneuploid cells in the nine tissues studied, from none in blood and ovary to 100% in spleen and liver. The trisomy arose meiotically with apparent post-zygotic loss of one of the chromosomes 12; uniparental disomy for this chromosome in the diploid cell line was excluded. The phenotype of the cases reported in living or liveborn individuals has been extremely variable, ranging from the present case, in which the child died in infancy with multiple malformations and pigmentary dysplasia, to a fortuitous finding in an adult studied for infertility. The variation in severity is probably determined by the proportion and distribution of the trisomic cells, which is linked to the timing of the non-disjunctional error.

Mild autosomal dominant hypophosphatasia: in utero presentation in two families.

We describe four pregnancies in two families in which mild hypophosphatasia, apparently transmitted as an autosomal dominant trait, manifested in utero as severe long bone bowing. Postnatally, there was spontaneous improvement of the skeletal defects. Recognition of this presentation for hypophosphatasia by family investigation and assessment of the fetal skeleton for degree of ossification and chest size using ultrasonography is important. The prognosis for this condition is considerably better than for more severe forms of hypophosphatasia and for many other disorders that cause skeletal defects with long bone bowing in utero.

Severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN): phenotypic analysis of a new skeletal dysplasia caused by a Lys650Met mutation in fibroblast growth factor receptor 3.

We previously discovered a novel missense mutation (Lys650Met) in the tyrosine kinase domain of the fibroblast growth factor receptor 3 (FGFR3) gene in four unrelated individuals with a condition we called "severe achondroplasia with developmental delay and acanthosis nigricans" (SADDAN) [Tavormina et al., 1999: Am. J. Hum. Genet. 64:722-731]. Here we present a more detailed clinical account of the SADDAN phenotype. The FGFR3 Lys650Met mutation results in severe disturbances in endochondral bone growth that approach and overlap those observed in thanatophoric dysplasia, type I. However, this mutation is most often compatible with survival into adulthood. Other unusual bone deformities, such as femoral bowing with reverse (i.e., posterior apex) tibial and fibular bowing and "ram's horn" bowing of the clavicle, are also seen in some patients. In addition to skeletal dysplasia, progressive acanthosis nigricans, and central nervous system structural anomalies, seizures and severe developmental delays are observed in surviving SADDAN patients. Despite its location within the same FGFR3 codon as the thanatophoric dysplasia type II mutation (Lys650Glu) and a similar effect on constitutive activation of the FGFR3 tyrosine kinase, the Lys650Met is not associated with cloverleaf skull or craniosynostosis.

Monodactylous limbs and abnormal genitalia are associated with hemizygosity for the human 2q31 region that includes the HOXD cluster.

Vertebrates have four clusters of Hox genes (HoxA, HoxB, HoxC, and HoxD). A variety of expression and mutation studies indicate that posterior members of the HoxA and HoxD clusters play an important role in vertebrate limb development. In humans, mutations in HOXD13 have been associated with type II syndactyly or synpolydactyly, and, in HOXA13, with hand-foot-genital syndrome. We have investigated two unrelated children with a previously unreported pattern of severe developmental defects on the anterior-posterior (a-p) limb axis and in the genitalia, consisting of a single bone in the zeugopod, either monodactyly or oligodactyly in the autopod of all four limbs, and penoscrotal hypoplasia. Both children are heterozygous for a deletion that eliminates at least eight (HOXD3-HOXD13) of the nine genes in the HOXD cluster. We propose that the patients' phenotypes are due in part to haploinsufficiency for HOXD-cluster genes. This hypothesis is supported by the expression patterns of these genes in early vertebrate embryos. However, the involvement of additional genes in the region could explain the discordance, in severity, between these human phenotypes and the milder, non-polarized phenotypes present in mice hemizygous for HoxD cluster genes. These cases represent the first reported examples of deficiencies for an entire Hox cluster in vertebrates and suggest that the diploid dose of human HOXD genes is crucial for normal growth and patterning of the limbs along the anterior-posterior axis.

Evaluation of mental retardation: recommendations of a Consensus Conference: American College of Medical Genetics.

A Consensus Conference utilizing available literature and expert opinion sponsored by the American College of Medical Genetics in October 1995 evaluated the rational approach to the individual with mental retardation. Although no uniform protocol replaces individual clinician judgement, the consensus recommendations were as follows: 1. The individual with mental retardation, the family, and medical care providers benefit from a focused clinical and laboratory evaluation aimed at establishing causation and in providing counseling, prognosis, recurrence risks, and guidelines for management. 2. Essential elements of the evaluation include a three-generation pedigree: pre-, peri-, and post-natal history, complete physical examination focused on the presence of minor anomalies, neurologic examination, and assessment of the behavioral phenotype. 3. Selective laboratory testing should, in most patients, include a banded karyotype. Fragile X testing should be strongly considered in both males and females with unexplained mental retardation, especially in the presence of a positive family history, a consistent physical and behavioral phenotype and absence of major structural abnormalities. Metabolic testing should be initialed in the presence of suggestive clinical and physical findings. Neuroimaging should be considered in patients without a known diagnosis especially in the presence of neurologic symptoms, cranial contour abnormalities, microcephaly, or macrocephaly. In most situations MRI is the testing modality of choice. 4. Sequential evaluation of the patient, occasionally over several years, is often necessary for diagnosis, allowing for delineation of the physical and behavioral phenotype, a logical approach to ancillary testing and appropriate prognostic and reproductive counseling.

Tenascin-X deficiency is associated with Ehlers-Danlos syndrome.

The tenascins are a family of large extracellular matrix proteins with at least three members: tenascin-X (TNX), tenascin-C (TNC, or cytotactin) and tenascin-R (TN-R, or restrictin). Although the tenascins have been implicated in a number of important cellular processes, no function has been clearly established for any tenascin. We describe a new contiguous-gene syndrome, involving the CYP21B and TNX genes, that results in 21-hydroxylase deficiency and a connective-tissue disorder consisting of skin and joint hyperextensibility, vascular fragility and poor wound healing. The connective tissue findings are typical of the Ehlers-Danlos syndrome (EDS). The abundant expression of TNX in connective tissues is consistent with a role in EDS, and our patient's skin fibroblasts do not synthesize TNX protein in vitro or in vivo. His paternal allele carries a novel deletion arising from recombination between TNX and its partial duplicate gene, XA, which precludes TNX synthesis. Absence of TNX mRNA and protein in the proband, mapping of the TNX gene and HLA typing of this family suggest recessive inheritance of TNX deficiency and connective-tissue disease. Although the precise role of TNX in the pathogenesis of EDS is uncertain, this patient's findings suggest a unique and essential role for TNX in connective-tissue structure and function.

Macrocephaly-cutis marmorata telangiectatica congenita: a distinct disorder with developmental delay and connective tissue abnormalities.

We describe 13 unrelated children with abnormalities of somatic growth, face, brain, and connective tissue including vasculature. Although the condition in these children falls under the general group of disorders known as cutis marmorata telangiectatica congenita (CMTC), the constellation of abnormalities appears to constitute a distinct and easily recognizable phenotype within this general group. In contrast to most children reported with CMTC, children in this subgroup have a high risk for neurologic abnormalities, including developmental delay, mental retardation, megalencephaly, and hydrocephalus. Early recognition of this condition is important for appropriate surveillance for known complications and parental counseling.

Ritscher-Schinzel (3C) syndrome: documentation of the phenotype.

Ritscher-Schinzel syndrome or 3C (craniocerebello-cardiac) syndrome is characterized by cardiac defects, cerebellar vermis hypoplasia, and cranial defects. Nineteen cases were reported previously; however, the full spectrum of this disorder has not been determined. We have evaluated two unrelated males with this condition. Both had defects of the endocardial cushion and vermis hypoplasia with hypotonia. In addition, both had hypospadias, a previously undescribed finding of this disorders. Review of the previously reported cases and those described herein demonstrate: 1) Although varying degrees of vermis hypoplasia are accompanied by hypotonia, delayed gross motor function improves with advancing age leaving speech delay as the major neurodevelopmental handicap. 2) Two different types of cardiac anomalies occur: defects of the endocardial cushion ranging from anomalies of the mitral or tricuspid valves to complete AV canal, and/or conotruncal defects. 3) Postnatal growth deficiency was seen in most patients in whom longitudinal information was available. In our review of patients with vermis hypoplasia we ascertained a patient diagnosed as having "Joubert syndrome" who had most findings of the Ritscher-Schinzel syndrome and several other patients with "Dandy-Walker syndrome" who likely have had Ritscher-Schinzel syndrome, suggesting that Ritscher-Schinzel syndrome is more common than has been appreciated. Careful search for the subtle facial changes characteristic of this disorder as well as coloboma, cleft palate/bifid uvula, short neck, syndactyly, and hypoplasia of the nails is warranted when evaluating children with Dandy-Walker malformation with or without clinical signs of Joubert syndrome.

Is there an association of Down syndrome and omphalocele?

The possible association of Down syndrome (DS) with omphalocele is controversial. We reviewed the 2,979 live births and stillbirths with DS born from 1983 to 1993 in the catchment area of the California Birth Defects Monitoring Program (CBDMP). We observed one infant with both defects, a number that did not differ significantly from what was expected (P < 0.40). We also reviewed the pathological reports of one of us (L.H.H.) from a series of 36 DS fetuses and neonatal deaths; none had an omphalocele. We then reviewed the literature for epidemiological studies of DS and for epidemiological, surgical, prenatal, and familial studies of omphalocele. Possible biases inherent in each type of study were evaluated. The majority of epidemiological studies showed no association of DS with omphalocele. In surgical series, the occasional infant with both defects was more likely to undergo surgery than infants with omphalocele and trisomies 13 and 18 or other severe birth defects. Inclusion of both omphalocele and umbilical hernia in the same ICD-9 code may explain some of the correlations with DS noticed in a few epidemiological studies. In conclusion, our data suggest that trisomy 21 does not predispose the fetus to an increased risk for an omphalocele.

Maternal medications and environmental exposures as risk factors for gastroschisis.

In a case-control study of gastroschisis, we evaluated the risks associated with mother's first-trimester use of medications and with hobby or occupational exposures for 110 cases and 220 controls without a birth defect. Mothers of cases and controls were age-matched. For hobby or occupational exposures, we found significantly elevated risks for high levels of solvents (odds ratio (OR) = 3.8; 95% confidence interval (CI) = 1.6-9.2) and for colorants (OR = 2.3; 95% CI = 1.3-4.0). For medications, we found significantly elevated risks for two strong cyclooxygenase inhibitors, aspirin (OR = 4.7; 95% CI = 1.2-18.1) and ibuprofen (OR = 4.0; 95% CI = 1.0-16.0), but not for acetaminophen, a weak cyclooxygenase inhibitor. Periconceptional exposure to X rays was also associated with gastroschisis (OR = 2.5; 95% CI = 1.2-5.5), but exposure to antibiotics, antinauseants, sulfonamides, or oral contraceptives was not. We also found elevated risks for two decongestants, pseudoephedrine (OR = 2.1; 95% CI = 0.8-5.5) and phenylpropanolamine (OR = 10.0; 95% CI = 1.2-85.6). For the group of all decongestants, including also oxymetazoline and ephedrine, the risk was significantly elevated (OR = 2.4; 95% CI = 1.0-5.4). Controlling in multivariate analyses for several demographic and pregnancy variables associated with gastroschisis in a previous analysis [Torfs et al. (1994) Teratology 50: 44-53] did not substantially change the level or direction of the associations. Most of these associations are for vasoactive substances, which supports a vascular hypothesis for the pathogenesis of gastroschisis.

Population-based study of tracheoesophageal fistula and esophageal atresia.

From a multiracial population of 1,035,384 births monitored by the California Birth Defects Monitoring Program (CBDMP) from 1983 to 1988, we ascertained 34 cases of esophageal atresia (EA), 204 cases of tracheoesophageal fistula (TEF) with an EA (TEF/EA), and 54 cases of TEF without EA. The total prevalence rate was 2.82 per 10,000 live births and stillbirths and showed no secular trend nor marked seasonal variation. Rates of multiple birth were high for each defect (TEF 3.7%, TEF/EA 4.9%, EA 8.8%; population 1.1%). Non-Hispanic whites were overrepresented for TEF and TEF/EA, but not for EA. Excluding trisomies, mean maternal age was above the population mean (26.8 years) for TEF (27.9 years) and TEF/EA (28.0 years), but not for EA (26.2 years). The proportion of trisomies was significantly higher for EA (23.5%) than for TEF (9.3%; P < 0.02) or for TEF/EA (7.4%; P < 0.003). We subdivided each defect into five mutually exclusive types: isolated, multiple, syndromic, chromosomal, and trisomic. Male-to-female (M/F) ratios varied considerably between types, both within and between defects. The highest M/F ratios within each defect were for the multiple type (TEF 2.29, TEF/EA 1.44, EA 1.33; population 1.05), and the lowest for trisomies (TEF 0.25; TEF/EA 0.25, and EA 0.60). All types except trisomies were significantly associated with a single umbilical artery. We found an association of EA and TEF/EA with dextrocardia (3.1% of cases), and confirmed the association of primary hydrocephalus with TEF and TEF/EA (2.7% of cases). The proportion of cases with additional midline defects or VATER or VACTERL type anomalies was similar for all three defects, suggesting a common developmental pathogenesis. Epidemiologic differences between defects, and between types within defects, may reflect differences in timing of the pathological process or differences in susceptibilities (e.g., by sex or aneuploidy) and emphasize the need to evaluate each defect and its types separately in epidemiologic studies.

Neurofibromatosis-Noonan syndrome.

Type I neurofibromatosis (NF-1) and Noonan syndrome (NS) are two fairly common genetic disorders. Patients with features of both disorders have been described, but considerable variability of phenotypic expression occurs. As a result, the correct nosology of this syndrome is uncertain. We present a patient with full expression of both NF-1 and NS phenotypes, and discuss the debate regarding the genetics of the combined syndrome.

D-2-hydroxyglutaric aciduria.

Hydroxyglutaric aciduria is detected by gas chromatographic-mass spectrometric analysis, and the D and L forms are quantified by chemical ionization with deuterated internal standards. Patients have recently been described who accumulate the D form, and they appear to be quite different from those with the more common L form. Experience is reported with three patients and an animal model with D-2-hydroxyglutaric aciduria. The phenotype appears to include mental retardation, macrocephaly, hypotonia, seizures, and involuntary movements, although neurologic and systemic manifestations of the disorder varied considerably between individual patients, even within the same family.