Laurie H. Seaver

Mutations in FOXC2 (MFH-1), a Forkhead Family Transcription Factor, Are Responsible for the Hereditary Lymphedema-Distichiasis Syndrome

Lymphedema-distichiasis (LD) is an autosomal dominant disorder that classically presents as lymphedema of the limbs, with variable age at onset, and double rows of eyelashes (distichiasis). Other complications may include cardiac defects, cleft palate, extradural cysts, and photophobia, suggesting a defect in a gene with pleiotrophic effects acting during development. We previously reported neonatal lymphedema, similar to that in Turner syndrome, associated with a t(Y;16)(q12;q24.3) translocation. A candidate gene was not found on the Y chromosome, and we directed our efforts toward the chromosome 16 breakpoint. Subsequently, a gene for LD was mapped, by linkage studies, to a 16-cM region at 16q24.3. By FISH, we determined that the translocation breakpoint was within this critical region and further narrowed the breakpoint to a 20-kb interval. Because the translocation did not appear to interrupt a gene, we considered candidate genes in the immediate region that might be inactivated by position effect. In two additional unrelated families with LD, we identified inactivating mutations-a nonsense mutation and a frameshift mutation-in the FOXC2 (MFH-1) gene. FOXC2 is a member of the forkhead/winged-helix family of transcription factors, whose members are involved in diverse developmental pathways. FOXC2 knockout mice display cardiovascular, craniofacial, and vertebral abnormalities similar to those seen in LD syndrome. Our findings show that FOXC2 haploinsufficiency results in LD. FOXC2 represents the second known gene to result in hereditary lymphedema, and LD is only the second hereditary disorder known to be caused by a mutation in a forkhead-family gene.

DECLINE IN PREVALENCE OF NEURAL TUBE DEFECTS IN A HIGH-RISK REGION OF THE UNITED STATES

Objectives. To conduct surveillance for neural tube defects (NTDs) in a high-risk region of the United States and to prevent occurrence and recurrence of NTDs through the periconceptional use of folic acid supplements. Design. Active and passive methods were used for surveillance of NTD-affected pregnancies and births during a 6-year period (October 1992–September 1998). Individual genetic counseling was used to prevent NTD recurrences and a public awareness campaign was used to reduce NTD occurrences. Setting. State of South Carolina. Patients. All cases of spina bifida, anencephaly, and encephalocele identified among 278 122 live births and fetal deaths to South Carolina residents during 1992–1998 were included. Main Outcome Measure. Changes in occurrence and recurrence rates during a 6-year period. Results. Over the 6 years of surveillance, the prevalence rates for NTDs decreased from 1.89 to .95 cases per 1000 live births and fetal deaths. The prevalence decrease is explained primarily by a decrease in cases of spina bifida. Isolated NTDs accounted for 297/360 (82%) NTDs and 63/360 (18%) had at least 1 other structural anomaly. Females predominated among isolated NTDs but the sex distribution was equal among NTD cases with other anomalies. Prevalence rates for whites (1.48 cases per 1000 live births and fetal deaths) were higher than rates for blacks (.87 cases per 1000 live births and fetal deaths). There were no NTD recurrences in 113 subsequent pregnancies to mothers of infants with isolated NTDs who took periconceptional folic acid. The rate of periconceptional folic acid use among women of childbearing years increased from 8% to 35% during the 6-year project period. Conclusion. The prevalence of NTDs in a high-risk region has declined coincident with the increased periconceptional use of folic acid supplements among women of childbearing age.neural tube defects, high-risk region, birth defects, folic acid, spina bifida, anencephaly, encephalocele.

Isolated hemihyperplasia (hemihypertrophy): Report of a prospective multicenter study of the incidence of neoplasia and review

Hemihyperplasia is characterized by asymmetric growth of cranium, face, trunk, limbs, and/or digits, with or without visceral involvement. It may be an isolated finding in an otherwise normal individual, or it may occur in several syndromes. Although isolated hemihyperplasia (IHH) is of unknown cause, it may represent one end of the clinical spectrum of the Wiedemann-Beckwith syndrome (WBS). Uniparental paternal disomy of 11p15.5 or altered expression of insulin-like growth factor 2 (IGF2) from the normally silent maternal allele have been implicated as causes of some cases of WBS. IHH and other mild manifestations of WBS may represent patchy overexpression of the IGF2 gene following defective imprinting in a mosaic fashion. The natural history of IHH varies markedly. An association among many overgrowth syndromes and a predisposition to neoplasia is well recognized. Heretofore the risk for tumor development in children with IHH was unknown. We report on the results of a prospective multicenter clinical study of the incidence and nature of neoplasia in children evaluated because of IHH. One hundred sixty-eight patients were ascertained. A total of 10 tumors developed in nine patients, for an overall incidence of 5.9%. Tumors were of embryonal origin (similar to those noted in other overgrowth disorders), including Wilms tumor, hepatoblastoma, adrenal cell carcinoma, and leiomyosarcoma of the small bowel in one case. These data support a tumor surveillance protocol for children with IHH similar to that performed in other syndromes associated with overgrowth.

Inverted genomic segments and complex triplication rearrangements are mediated by inverted repeats in the human genome.

We identified complex genomic rearrangements consisting of intermixed duplications and triplications of genomic segments at the MECP2 and PLP1 loci. These complex rearrangements were characterized by a triplicated segment embedded within a duplication in 11 unrelated subjects. Notably, only two breakpoint junctions were generated during each rearrangement formation. All the complex rearrangement products share a common genomic organization, duplication-inverted triplication-duplication (DUP-TRP/INV-DUP), in which the triplicated segment is inverted and located between directly oriented duplicated genomic segments. We provide evidence that the DUP-TRP/INV-DUP structures are mediated by inverted repeats that can be separated by >300 kb, a genomic architecture that apparently leads to susceptibility to such complex rearrangements. A similar inverted repeat–mediated mechanism may underlie structural variation in many other regions of the human genome. We propose a mechanism that involves both homology-driven events, via inverted repeats, and microhomologous or nonhomologous events.

Mutations in FKBP10, which result in Bruck syndrome and recessive forms of osteogenesis imperfecta, inhibit the hydroxylation of telopeptide lysines in bone collagen

Although biallelic mutations in non-collagen genes account for <10% of individuals with osteogenesis imperfecta, the characterization of these genes has identified new pathways and potential interventions that could benefit even those with mutations in type I collagen genes. We identified mutations in FKBP10, which encodes the 65 kDa prolyl cis-trans isomerase, FKBP65, in 38 members of 21 families with OI. These include 10 families from the Samoan Islands who share a founder mutation. Of the mutations, three are missense; the remainder either introduce premature termination codons or create frameshifts both of which result in mRNA instability. In four families missense mutations result in loss of most of the protein. The clinical effects of these mutations are short stature, a high incidence of joint contractures at birth and progressive scoliosis and fractures, but there is remarkable variability in phenotype even within families. The loss of the activity of FKBP65 has several effects: type I procollagen secretion is slightly delayed, the stabilization of the intact trimer is incomplete and there is diminished hydroxylation of the telopeptide lysyl residues involved in intermolecular cross-link formation in bone. The phenotype overlaps with that seen with mutations in PLOD2 (Bruck syndrome II), which encodes LH2, the enzyme that hydroxylates the telopeptide lysyl residues. These findings define a set of genes, FKBP10, PLOD2 and SERPINH1, that act during procollagen maturation to contribute to molecular stability and post-translational modification of type I procollagen, without which bone mass and quality are abnormal and fractures and contractures result.

Mutations in PIEZO2 Cause Gordon Syndrome, Marden-Walker Syndrome, and Distal Arthrogryposis Type 5

Gordon syndrome (GS), or distal arthrogryposis type 3, is a rare, autosomal-dominant disorder characterized by cleft palate and congenital contractures of the hands and feet. Exome sequencing of five GS-affected families identified mutations in piezo-type mechanosensitive ion channel component 2 (PIEZO2) in each family. Sanger sequencing revealed PIEZO2 mutations in five of seven additional families studied (for a total of 10/12 [83%] individuals), and nine families had an identical c.8057G>A (p.Arg2686His) mutation. The phenotype of GS overlaps with distal arthrogryposis type 5 (DA5) and Marden-Walker syndrome (MWS). Using molecular inversion probes for targeted sequencing to screen PIEZO2, we found mutations in 24/29 (82%) DA5-affected families and one of two MWS-affected families. The presence of cleft palate was significantly associated with c.8057G>A (Fishers exact test, adjusted p value < 0.0001). Collectively, although GS, DA5, and MWS have traditionally been considered separate disorders, our findings indicate that they are etiologically related and perhaps represent variable expressivity of the same condition.

Limb–body wall defect. Is there a defensible hypothesis and can it explain all the associated anomalies?†

Aside from gastroschisis and omphalocele, major defects of the ventral body (thoracoabdominal) wall are relatively uncommon and almost universally lethal. They are most often associated with other anomalies including those of the limbs that may range from amelia to mild positional deformations, unusual craniofacial malformations, and a variety of visceral abnormalities that include the heart, lungs, genitourinary system, and gut. This complex of ventral wall anomalies has been discussed under a broad and changing nomenclature that has included amniotic band disruption complex, amnion rupture sequence, limb–body wall defect (or complex), and simply body wall complex. Three major theories have been suggested to explain this complex: early amnion rupture (operating through uterine pressure and/or disruption by amniotic bands), vascular compromise (primarily hypoperfusion), and an early intrinsic defect of the developing embryo. We present four patients that illustrate the spectrum of ventral body wall defects, and from there critique the current hypotheses of pathogenesis. We conclude that this association of malformations originates as early as the embryonic disc stage, and that some of the observed associated anomalies are secondary complications of the primary disturbance in embryogenesis. We propose a new explanation for the atypical facial clefts and cranial malformations that are often observed.

ACMG practice guideline: Genetic evaluation of short stature

Short stature is a common indication for genetic evaluation. The differential diagnosis is broad and includes both pathologic causes of short stature and nonpathologic causes. The purpose of genetic evaluation for short stature is to provide accurate diagnosis for medical management and to provide prognosis and recurrence risk counseling for the patient and family. There is no evidence-based data to guide the geneticist in an efficient, cost-effective approach to the evaluation of a patient with short stature. This guideline provides a rubric for the evaluation of short stature evaluation and summarizes common diagnoses and clinical testing available.

Indications for genetic referral: a guide for healthcare providers

Disclaimer: This guideline is designed primarily as an educational resource for medical geneticists and other healthcare providers to help them provide quality medical genetic services. Adherence to this guideline does not necessarily assure a successful medical outcome. This guideline should not be considered inclusive of all proper procedures and tests or exclusive of other procedures and tests that are reasonably directed to obtaining the same results. In determining the propriety of any specific procedure or test, the geneticist should apply his or her own professional judgment to the specific clinical circumstances presented by the individual patient or specimen. It may be prudent, however, to document in the patients record the rationale for any significant deviation from this guideline.

Toriello-Carey syndrome: Delineation and review

Toriello and Carey [1988: Am J Med Genet 31:17–23] first described a syndrome with component manifestations of corpus callosum agenesis, unusual facial appearance, Robin sequence, and other anomalies. This was termed the Toriello–Carey syndrome by Lacombe et al. [1992: Am J Med Genet 42:374–376]. Since then, 11 reports describing 16 additional children have been published; in addition, we have had the opportunity to review over 30 unpublished cases. However, for various reasons, only 25 of the unpublished patients were included in this review. Based on this total, we can begin to better delineate this syndrome, as well as provide some information on natural history.