Sevim Balci

Mutation of the gene encoding the ROR2 tyrosine kinase causes autosomal recessive Robinow syndrome.

Robinow syndrome is a short-limbed dwarfism characterized by abnormal morphogenesis of the face and external genitalia, and vertebral segmentation. The recessive form of Robinow syndrome (RRS; OMIM 268310), particularly frequent in Turkey, has a high incidence of abnormalities of the vertebral column such as hemivertebrae and rib fusions, which is not seen in the dominant form. Some patients have cardiac malformations or facial clefting. We have mapped a gene for RRS to 9q21–q23 in 11 families. Haplotype sharing was observed between three families from Turkey, which localized the gene to a 4.9-cM interval. The gene ROR2, which encodes an orphan membrane-bound tyrosine kinase, maps to this region. Heterozygous (presumed gain of function) mutations in ROR2 were previously shown to cause dominant brachydactyly type B (BDB; ref. 7). In contrast, Ror2−/− mice have a short-limbed phenotype that is more reminiscent of the mesomelic shortening observed in RRS. We detected several homozygous ROR2 mutations in our cohort of RRS patients that are located upstream from those previously found in BDB. The ROR2 mutations present in RRS result in premature stop codons and predict nonfunctional proteins.

Mutations in the Gene Encoding Capillary Morphogenesis Protein 2 Cause Juvenile Hyaline Fibromatosis and Infantile Systemic Hyalinosis

Juvenile hyaline fibromatosis (JHF) and infantile systemic hyalinosis (ISH) are autosomal recessive conditions characterized by multiple subcutaneous skin nodules, gingival hypertrophy, joint contractures, and hyaline deposition. We previously mapped the gene for JHF to chromosome 4q21. We now report the identification of 15 different mutations in the gene encoding capillary morphogenesis protein 2 (CMG2) in 17 families with JHF or ISH. CMG2 is a transmembrane protein that is induced during capillary morphogenesis and that binds laminin and collagen IV via a von Willebrand factor type A (vWA) domain. Of interest, CMG2 also functions as a cellular receptor for anthrax toxin. Preliminary genotype-phenotype analyses suggest that abrogation of binding by the vWA domain results in severe disease typical of ISH, whereas in-frame mutations affecting a novel, highly conserved cytoplasmic domain result in a milder phenotype. These data (1) demonstrate that JHF and ISH are allelic conditions and (2) implicate perturbation of basement-membrane matrix assembly as the cause of the characteristic perivascular hyaline deposition seen in these conditions.

A specific mutation in the distant sonic hedgehog (SHH) cis-regulator (ZRS) causes Werner mesomelic syndrome (WMS) while complete ZRS duplications underlie Haas type polysyndactyly and preaxial polydactyly (PPD) with or without triphalangeal thumb†

Werner mesomelic syndrome (WMS) is an autosomal dominant disorder with unknown molecular etiology characterized by hypo‐ or aplasia of the tibiae in addition to the preaxial polydactyly (PPD) of the hands and feet and/or five‐fingered hand with absence of thumbs. We show that point mutations of a specific nucleotide within the sonic hedgehog (SHH) regulatory region (ZRS) cause WMS. In a previously unpublished WMS family, we identified the causative G>A transition at position 404 of the ZRS, and in six affected family members of a second WMS family we found a 404G>C mutation of the ZRS. The 404G>A ZRS mutation is known as the “Cuban mutation” of PPD type II (PPD2). Interestingly, the index patient of that family had tibial hypoplasia as well. These data provide the first evidence that WMS is caused by a specific ZRS mutation, which leads to strong ectopic SHH expression. In contrast, we show that complete duplications of the ZRS region lead to type Haas polysyndactyly or triphalangeal thumb‐polysyndactyly syndrome, but do not affect lower limb development. We suggest the term “ZRS‐associated syndromes” and a clinical subclassification for the continuum of limb malformations caused by different molecular alterations of the ZRS. Hum Mutat 30:1–9, 2009.

Disruption of ALX1 Causes Extreme Microphthalmia and Severe Facial Clefting: Expanding the Spectrum of Autosomal-Recessive ALX-Related Frontonasal Dysplasia

We present an autosomal-recessive frontonasal dysplasia (FND) characterized by bilateral extreme microphthalmia, bilateral oblique facial cleft, complete cleft palate, hypertelorism, wide nasal bridge with hypoplasia of the ala nasi, and low-set, posteriorly rotated ears in two distinct families. Using Affymetrix 250K SNP array genotyping and homozygosity mapping, we mapped this clinical entity to chromosome 12q21. In one of the families, three siblings were affected, and CNV analysis of the critical region showed a homozygous 3.7 Mb deletion containing the ALX1 (CART1) gene, which encodes the aristaless-like homeobox 1 transcription factor. In the second family we identified a homozygous donor-splice-site mutation (c.531+1G > A) in the ALX1 gene, providing evidence that complete loss of function of ALX1 protein causes severe disruption of early craniofacial development. Unlike loss of its murine ortholog, loss of human ALX1 does not result in neural-tube defects; however, it does severely affect the orchestrated fusion between frontonasal, nasomedial, nasolateral, and maxillary processes during early-stage embryogenesis. This study further expands the spectrum of the recently recognized autosomal-recessive ALX-related FND phenotype in humans.

ALX4 dysfunction disrupts craniofacial and epidermal development

Genetic control of craniofacial morphogenesis requires a complex interaction of numerous genes encoding factors essential for patterning and differentiation. We present two Turkish families with a new autosomal recessive frontofacial dysostosis syndrome characterized by total alopecia, a large skull defect, coronal craniosynostosis, hypertelorism, severely depressed nasal bridge and ridge, bifid nasal tip, hypogonadism, callosal body agenesis and mental retardation. Using homozygosity mapping, we mapped the entity to chromosome 11p11.2-q12.3 and subsequently identified a homozygous c.793C-->T nonsense mutation in the human ortholog of the mouse aristaless-like homeobox 4 (ALX4) gene. This mutation is predicted to result in a premature stop codon (p.R265X) of ALX4 truncating 146 amino acids of the protein including a part of the highly conserved homeodomain and the C-terminal paired tail domain. Although the RNA is stable and not degraded by nonsense-mediated RNA decay, the mutant protein is likely to be non-functional. In a skin biopsy of an affected individual, we observed a hypomorphic interfollicular epidermis with reduced suprabasal layers associated with impaired interfollicular epidermal differentiation. Hair follicle-like structures were present but showed altered differentiation. Our data indicate that ALX4 plays a critical role both in craniofacial development as in skin and hair follicle development in human.

Dermatological manifestations of 71 Down syndrome children admitted to a clinical genetics unit

Seventy‐one children with Down syndrome who were admitted consecutively to Hacettepe University Childrens Hospital Genetics Department were examined for skin disorders. None of the patients suffered directly from skin disorders. All were living with their families and had approximately similar living conditions. There were 29 children with palmoplantar hyperkeratosis (40.8%), seven with xerosis (9.8%), 22 with seborrheic dermatitis (30.9%), 14 with fissured tongue (20%), eight with geographic tongue (11.2%), and nine with cutis marmorata (12.6%). Nine had normal skin findings. Since palmoplantar hyperkeratosis may be a result of vitamin A deficiency, the serum vitamin A levels of these patients were evaluated. There was no statistical difference between vitamin A levels of the children with Down syndrome and the control group.

Three sibs diagnosed prenatally with situs inversus totalis, renal and pancreatic dysplasia, and cysts

Recently we described a previously apparently undescribed autosomal recessive syndrome in two sib fetuses with situs inversus totalis, cystic dysplastic kidneys and pancreas, bowing of the lower limbs and clavicles, severe intrauterine growth retardation, and oligohydramnios. This syndrome differs from that of Ivemark and related syndromes due to lack of liver involvement. After these two sibs, this consanguineous family had a third child and an early prenatal diagnosis of pancreatic and dysplastic renal cysts was made in the 19.5-week-old fetus. The last case supports the genetic hypothesis.

A NEW SYNDROME OF DYSMORPHOGENESIS: IMPERFORATE‐ANUS ASSOCIATED WITH POLY‐OLIGODACTYLY AND SKELETAL (MAINLY VERTEBRAL) ANOMALIES

Nine patients having imperforate anus and hand malformations with or without vertebral anomalies have been presented. The similarity of the findings in these patients to those seen among the members of the luxoid group of mouse mutants, such as the dominant hemimelia (Dh) mutants has been emphasized. Similar cases reported in the literature have been briefly reviewed.

Incidence of Congenital Malformations in a Sample of the Turkish Population

10,000 liveborn babies resulting from preg nancies of 28 of more weeks were examined by a team of 3 pediatricians, 1 orthopedic surgeon, 1 pediatric cardiologist, and 1 urologist in order to find the incidence of various congenital malformations. Relatively high incidence rates for imperforate anus and polydactyly were encountered (1.1 and 2.6/1,000 births, respectively). The rates for anencephaly and congenital heart disease were also found to be somewhat higher than those reported for most white populations.

Ring chromosome 4 and Wolf-Hirschhorn syndrome (WHS) in a child with multiple anomalies.

We report on a 16‐month‐old male patient with ring chromosome 4 and deletion of Wolf–Hirschhorn syndrome (WHS) region with multiple congenital anomalies including unilateral cleft lip and palate, iris coloboma, microcephaly, midgut malrotation, hypospadias, and double urethral orifices. Peripheral chromosome analysis of the patient showed 46,XY,r(4)(p16.3q35) de novo. Multicolor fluorescence in situ hybridization (FISH) study was also performed and according to multicolor banding (MCB) a r(4)(::p16.3 → q34.3 ∼ 35.1::) was found in all metaphases. Subtelomeric 4p region, subtelomeric 4q region, as well as, Wolf–Hirschhorn critical region were deleted in ring chromosome 4. Genomic microarray analysis was also performed to delineate the size of deletion. Cranial magnetic resonance imaging (MRI) showed hypoplastic corpus callosum, delayed myelinization, and frontal and occipital lobe atrophies. Both maternal and paternal chromosomal analyses were normal. We compare the phenotypic appearance of our patient with the previously reported 16 cases of ring chromosome 4 in the medical literature.