Libin Mei

Targeted next-generation sequencing identifies novel compound heterozygous mutations of DYNC2H1 in a fetus with short rib-polydactyly syndrome, type III.

A 26-year-old woman with a past history of fetal skeletal dysplasia was referred to our institution at 24weeks of gestation following a routine sonographic diagnosis of short limbs in the fetus. A fetal ultrasound showed short limbs, a narrow thorax, short ribs with marginal spurs, and polydactyly. Conventional cytogenetics analysis of cultured amniocytes demonstrated that the fetal karyotype was normal. Using targeted exome sequencing of 226 known genes implicated in inherited skeletal dysplasia, we identified compound heterozygous mutations in the DYNC2H1 gene in the fetus with short rib-polydactyly syndrome, type III (SRPS III), c.1151 C>T(p.Ala384Val) and c.4351 C>T (p.Gln1451*), which were inherited from paternally and maternally, respectively. These variants were further confirmed using Sanger sequencing and have not been previously reported. To our knowledge, this is the first report of DYNC2H1 mutations causing SRPS III, in the Chinese population. Our findings expand the number of reported cases of this rare disease, and indicate that targeted next-generation sequencing (NGS) is an accurate, rapid, and cost-effective method in the genetic diagnosis of fetal skeletal dysplasia.

De novo exonic deletion of KDM6A in a Chinese girl with Kabuki syndrome: A case report and brief literature review

Kabuki syndrome (KS) is a rare condition with multiple congenital anomalies and mental retardation. Exonic deletions, disrupting the lysine (K)‐specific demethylase 6A (KDM6A) gene have been demonstrated as rare cause of KS. Here, we report a de novo 227‐kb deletion in chromosome Xp11.3 of a 7‐year‐old Chinese girl with KS. Besides the symptoms of KS, the patient also presented with skin allergic manifestations, which were considered to be a new, rare feature of the phenotypic spectrum. The deletion includes the upstream region and exons 1–2 of KDM6A and potentially causes haploinsuffiency of the gene. We also discuss the mutation spectrum of KDM6A and clinical variability of patients with KDM6A deletion through a literature review.

Pachygyria, seizures, hypotonia, and growth retardation in a patient with an atypical 1.33Mb inherited microduplication at 22q11.23.

22q11.2 microduplication syndrome was recently described as a new disorder with variable clinical features that ranged from normal to mental retardation and with congenital defects. According to published reports, majority of patients with 22q11.2 duplications inherit these from unaffected parents rather than by de novo mutations, which is different from most microduplication/microdeletion syndromes. In this study, we report a patient that carried a paternally inherited atypical 1.33Mb duplication at 22q11.23. The proband (or proposita) presented with hypotonia, feeding difficulties, intractable epilepsy, hearing disability, and pachygyria. A pachygyria phenotype had not been previously reported to be associated with a 22q11 microduplication syndrome. Cytogenetic and molecular genetic analyses based on standard G-banding, SNP array, and fluorescence in situ hybridization were performed for the proband and her parents. An atypical 1.33Mb duplication at 22q11.23 was detected in both the proband and her father. Thus, our findings verify the pathogenicity and diverse phenotypes of 22q11.2 microduplication and expand its phenotypic spectrum.

Clinical and molecular investigation in Chinese patients with glutaric aciduria type I.

Glutaric aciduria type I (GA-I) is a rare autosomal recessive metabolic disorder caused by deficiency of glutaryl-CoA dehydrogenase (GCDH), leading to an abnormal metabolism of lysine, hydroxylysine and tryptophan. It results in accumulations of glutaric acid, 3-hydroxyglutaric acid and glutaconic acid. Clinical features include the sudden onset of encephalopathy, hypotonia and macrocephaly usually before age 18months. Here we report five cases of GA-I confirmed with mutation analysis. GCDH gene mutations were identified in all five probands with GA-I. Three of them had compound heterozygous mutations and two had homozygous mutations. Mutations of two alleles (c.334G>T and IVS11-11A>G) were novel and both of them were confirmed to be splice site mutations by reverse transcription PCR.

Two novel NIPBL gene mutations in Chinese patients with Cornelia de Lange syndrome.

Cornelia de Lange syndrome (CdLS) is a dominantly inherited developmental disorder characterized by distinctive facial features, mental retardation, and upper limb defects, with the involvement of multiple organs and systems. To date, mutations have been identified in five genes responsible for CdLS: NIPBL, SMC1A, SMC3, RAD21, and HDAC8. Here, we present a clinical and molecular characterization of five unrelated Chinese patients whose clinical presentation is consistent with that of CdLS. There were no chromosomal abnormalities in the five children. In three patients, DNA sequencing revealed a previously reported frameshift mutation c.2479delA (p.Arg827GlyfsX20), and two novel mutations including a heterozygous mutation c.6272 G>T (p.Cys2091Phe) and a frameshift mutation c.1672delA (p.Thr558LeufsX7) in NIPBL. For the remaining patients, large deletions and/or duplications within the NIPBL gene were excluded as playing a role in the pathogenesis, by Multiplex Ligation-dependent Probe Amplification (MLPA) analysis. These findings broaden the mutation spectrum of NIPBL and further our understanding of the diverse and variable effects of NIPBL mutations on CdLS.

Notable Carrier Risks for Individuals Having Two Copies of SMN1 in Spinal Muscular Atrophy Families with 2-copy Alleles: Estimation Based on Chinese Meta-analysis Data

Spinal muscular atrophy is an autosomal recessive neuromuscular disease mainly caused by homozygous deletion of SMN1. The 2-copy SMN1 allele may present in the families of SMA patients with homozygous deletion of SMN1, one of whose parents has two SMN1 copies. In such families, individuals having two SMN1 copies still have a chance to be “2 + 0” carriers. In this study, the risks for the parents, fetuses and other siblings having two SMN1 copies to be “2 + 0” carriers were estimated based on Chinese meta-analysis data and turned out to be rather striking. Our findings would help to optimize genetic counseling regarding spinal muscular atrophy.

Morphometric analysis and developmental comparison of embryos from carriers with balanced chromosomal rearrangements in preimplantation genetic diagnosis cycles

The morphological parameters of embryos from 22 carriers with balanced chromosomal rearrangements (CRs) were quantified and evaluated to determine their possible link to chromosomal composition. The morphometric characteristics of 168 embryos diagnosed by fluorescence in situ hybridisation were measured using an imaging tool and then analysed retrospectively. The mean zygotic diameter of normal-balanced embryos was significantly smaller compared with that of abnormal embryos (P=0.015). In addition, the reduction in total cytoplasmic volume for Day-3 embryos was significantly lower in normal or balanced embryos than in abnormal embryos (P=0.027). Moreover, the pronuclear volumes of embryos that failed to reach the blastocyst stage were significantly smaller compared with those of blastocysts (P=0.016). These findings indicate that morphometric characteristics are correlated with developmental outcomes as well as with chromosomal composition in embryos from balanced CR carriers. However, an effective indicator of developmental outcomes may not accurately reflect chromosomal composition. Combining morphometric and traditional qualitative assessment may increase the precision and standardisation of embryo evaluation as well as contributing to improved efficiency of preimplantation genetic diagnosis by selecting embryos with high developmental potential and preferentially testing embryos predicted to have a low risk of chromosomal imbalance.

Novel de novo nonsense mutation of the PHEX gene (p.Lys50Ter) in a Chinese patient with hypophosphatemic rickets

X-linked hypophosphatemic rickets (XLHR), the most common form of inherited rickets, is a dominant disorder characterized by hypophosphatemia, abnormal bone mineralization, and short stature. Mutations in the PHEX gene are major causes of XLHR. Herein, we clinically characterized four unrelated families with hypophosphatemia, bone abnormalities, short stature, and dentin malformation. Mutational analysis of the PHEX gene using Sanger sequencing revealed three recurrent mutations (c.2197T>C, c.1646G>C, and c.2198G>A) and a de novo nonsense mutation (c.148A>T). The novel mutation was not found in any of the unaffected family members or in the 100 healthy controls and was predicted to produce a truncated protein (p.K50X), a truncated form of the PHEX protein caused by nonsense mutations has been frequently detected in XLHR individuals. Thus, our work indicated that the c.148A>T (p.K50X) mutation was the likely pathogenic mutation in individual III-2 in family 2, and that PHEX gene mutations were responsible for XLHR in these Chinese families. These findings expand the mutation spectrum of PHEX and may help us to understand the molecular basis of XLHR in order to facilitate genetic counseling.

Identification of a novel SHOX mutation in a Chinese family with isolated Madelung deformity

Madelung deformity is a pseudoautosomal dominant hereditary disorder characterized by the lateral and dorsal curvature of the distal radius, positive ulnar variance and proximal subsidence of the lunate (Anton et al. 1938; Arora and Chung 2006). It is frequently associated with Leri–Weill dyschondrosteosis (LWD) (Leri and Weill 1929), which is characterized by disproportionate short stature attributable to mesomelic shortening of the limbs. The Madelung deformity is a typical characteristic of LWD (Langer 1965; Herdman et al. 1966); however, the presence of the forearm deformity without any other clinical characteristics of dyschondrosteosis supports the diagnosis of isolated Madelung deformity (IMD). Individuals with IMD have normal height and body proportions, and the forearm anomaly is typically bilateral and symmetrical. IMD is progressive, is usually observed in adolescence, and occurs more commonly in females than males (Lichtenstein et al. 1980; Grigelioniene et al. 2001). IMD is caused by mutations of the short stature homeobox gene (SHOX, OMIM: 312865) (Ellison et al. 1997; Rao et al. 1997). In addition, mutations in the GNAS gene have also been reported to cause IMD (Rump et al. 2011). In this study, the clinical and radiographic features of a Chinese family with IMD is described. Mutation analysis of the SHOX gene indicated that a novel heterozygous deletion mutation of SHOX was responsible for the IMD disease in this family.