Identification of a molecular defect in a stillborn fetus with perinatal lethal hypophosphatasia using a disease-associated genome sequencing approach

Lethal skeletal disorders represent a heterogeneous and clinically variable group of genetic conditions, usually difficult to diagnose without post-mortem radiological assessment. Here we report on a stillborn patient delivered at 22 weeks of gestation who presented with severe skeletal symptoms comprising limb shortening and intrauterine fractures detected upon prenatal ultrasound and autopsy examination. Since post-mortem X-ray was refused and no phenotypic diagnosis could be attempted, we performed next-generation sequencing (NGS) of 2741 genes associated with all known Mendelian disorders. With this strategy, we were able to demonstrate the diagnosis at a molecular level, which turned out to be perinatal lethal hypophosphatasia (HPP). This severe form of HPP represents an inborn defect of ossification often resulting in stillbirth or postnatal death. The NGS panel revealed compound heterozygous ALPL missense mutations: c.1283G>C(p.Arg428Pro) and c.1363G>A(p.Gly455Ser). Mutations detected in our case, although previously described in other patients, have not been reported to co-occur in a single individual. The diagnosis established in our index using the NGS-based approach could have been successfully reached by standard radiography. Thus, our report points to the importance of X-ray examination in stillborn cases and highlights the emerging role of NGS strategies in the diagnostic process of prenatally manifesting skeletal disorders

Duplication of 10q24 locus: broadening the clinical and radiological spectrum

Split-hand-split-foot malformation (SHFM) is a rare condition that occurs in 1 in 8500-25,000 newborns and accounts for 15% of all limb reduction defects. SHFM is heterogeneous and can be isolated, associated with other malformations, or syndromic. The mode of inheritance is mostly autosomal dominant with incomplete penetrance, but can be X-linked or autosomal recessive. Seven loci are currently known: SHFM1 at 7q21.2q22.1 (DLX5 gene), SHFM2 at Xq26, SHFM3 at 10q24q25, SHFM4 at 3q27 (TP63 gene), SHFM5 at 2q31 and SHFM6 as a result of variants in WNT10B (chromosome 12q13). Duplications at 17p13.3 are seen in SHFM when isolated or associated with long bone deficiency. Tandem genomic duplications at chromosome 10q24 involving at least the DACTYLIN gene are associated with SHFM3. No point variant in any of the genes residing within the region has been identified so far, but duplication of exon 1 of the BTRC gene may explain the phenotype, with likely complex alterations of gene regulation mechanisms that would impair limb morphogenesis. We report on 32 new index cases identified by array-CGH and/or by qPCR, including some prenatal ones, leading to termination for the most severe. Twenty-two cases were presenting with SHFM and 7 with monodactyly only. Three had an overlapping phenotype. Additional findings were identified in 5 (renal dysplasia, cutis aplasia, hypogonadism and agenesis of corpus callosum with hydrocephalus). We present their clinical and radiological findings and review the literature on this rearrangement that seems to be one of the most frequent cause of SHFM

Duplication of PTHLH causes osteochondroplasia with a combined brachydactyly type E/A1 phenotype with disturbed bone maturation and rhizomelia

Parathyroid hormone-like hormone (PTHLH, MIM 168470) plays an important role in endochondral bone development and prevents chondrocytes from differentiating. Disease-causing variants and haploinsufficiency of PTHLH are known to cause brachydactyly type E and short stature. So far, three large duplications encompassing several genes including PTHLH associating with enchondromatas and acro-osteolysis have been described in the literature. Here, we report on a three-generation pedigree with short humerus, curved radius, and a specific type of severe brachydactyly with features of types E and A1 but without the enchondromatas and the acro-osteolysis. Microarray-based comparative genomic hybridization (array-CGH) revealed a 70-kb duplication on chromosome 12p11.22 encompassing only PTHLH. Our data extend the phenotypic spectrum associated with copy number variations of PTHLH, and this family is to our knowledge the first description harboring a microduplication encompassing only PTHLH

Duplication of 10q24 locus: broadening the clinical and radiological spectrum

International audienceSplit-hand-split-foot malformation (SHFM) is a rare condition that occurs in 1 in 8500-25,000 newborns and accounts for 15% of all limb reduction defects. SHFM is heterogeneous and can be isolated, associated with other malformations, or syndromic. The mode of inheritance is mostly autosomal dominant with incomplete penetrance, but can be X-linked or autosomal recessive. Seven loci are currently known: SHFM1 at 7q21.2q22.1 (DLX5 gene), SHFM2 at Xq26, SHFM3 at 10q24q25, SHFM4 at 3q27 (TP63 gene), SHFM5 at 2q31 and SHFM6 as a result of variants in WNT10B (chromosome 12q13). Duplications at 17p13.3 are seen in SHFM when isolated or associated with long bone deficiency. Tandem genomic duplications at chromosome 10q24 involving at least the DACTYLIN gene are associated with SHFM3. No point variant in any of the genes residing within the region has been identified so far, but duplication of exon 1 of the BTRC gene may explain the phenotype, with likely complex alterations of gene regulation mechanisms that would impair limb morphogenesis. We report on 32 new index cases identified by array-CGH and/or by qPCR, including some prenatal ones, leading to termination for the most severe. Twenty-two cases were presenting with SHFM and 7 with monodactyly only. Three had an overlapping phenotype. Additional findings were identified in 5 (renal dysplasia, cutis aplasia, hypogonadism and agenesis of corpus callosum with hydrocephalus). We present their clinical and radiological findings and review the literature on this rearrangement that seems to be one of the most frequent cause of SHFM