Four children with postnatally diagnosed mosaic trisomy 12: Clinical features, literature review, and current diagnostic capabilities of genetic testing.

Children or adults with mosaic trisomy 12 diagnosed postnatally are extremely rare. Only a small number of patients with this mosaicism have been reported in the literature. The clinical manifestation of mosaic trisomy 12 is variable, ranging from mild developmental delay to severe congenital anomaly and neonatal death. The trisomy 12 cells are not usually able to be detected by phytohemagglutinin stimulated peripheral blood chromosome analysis. The variability of phenotypes and the limited number of patients with this anomaly pose a challenge to predict the clinical outcomes. In this study, we present the phenotypes and laboratory findings in four patients and review the 11 previously reported patients with mosaic trisomy 12 diagnosed postnatally, as well as 11 patients with mosaic trisomy 12 diagnosed prenatally. The findings of this study provide useful information for laboratory diagnosis and clinical management of these patients.

Partial 5p Deletion and Partial 5q Duplication in a Patient with Multiple Congenital Anomalies: A Two-Step Mechanism in Chromosomal Rearrangement Mediated by Non-Allelic Homologous Recombination.

We describe a 5-month-old female who presented with clinical features of 5p deletion syndrome, including high-pitched cry, microcephaly, micrognathia, bilateral preauricular tags, bifid uvula, abnormal palmar creases, bilateral hypoplastic nipples, feeding difficulties, and developmental delay. In addition, the patient also had a cardiac defect, proximal esophageal atresia, and distal tracheoesophageal fistula. aCGH of the patient revealed a 22.9-Mb deletion of chromosome 5p15.33p14.3 and an 8.28-Mb duplication of chromosome 5q12.1q13.2. Parental chromosome analysis indicated that these alterations are de novo. Chromosome and FISH analysis demonstrated that the 5q12.1q13.2 duplicated segment was attached to the 5p14.3 region with the band 5q12.1 more distal to the centromere than the band 5q13.2. Based on the bioinformatic analysis, we postulate a mechanism for the formation of this complex rearrangement of chromosome 5 by 2-step-wise events mediate by nonallelic homologous recombination between low copy repeats. To the best of our knowledge this rearrangement found in our patient has not been reported in the literature. This report demonstrates the value of chromosome analysis in conjunction with FISH and aCGH for identification of complex rearrangements which cannot be revealed by array analysis alone.

Novel NLRC4 Mutation Causes a Syndrome of Perinatal Autoinflammation With Hemophagocytic Lymphohistiocytosis, Hepatosplenomegaly, Fetal Thrombotic Vasculopathy, and Congenital Anemia and Ascites.

Autoinflammatory diseases are caused by pathologic activation of the innate immune system. Primary hemophagocytic lymphohistiocytosis (HLH) is an aggressive syndrome of excessive immune activation caused by monogenic mutations resulting in cytotoxic cell defects and subsequent failure to eliminate activated macrophages. Secondary HLH is often diagnosed in cases without a known Mendelian inheritance. However, some cases of "secondary" HLH have been shown to harbor mutations with partial dysfunction of the cytotoxic system. Recently, macrophage intrinsic abnormalities caused by NLRC4 inflammasome mutations have been linked to autoinflammation and recurrent macrophage activation syndromes resembling a primary HLH. We report a case of a former 28-week preterm infant with congenital anemia, ascites, and a heavy edematous placenta with fetal thrombotic vasculopathy, who developed hepatosplenomegaly and unexplained systemic inflammation with laboratory features of HLH in the early postnatal course and died at 2 months of age. Postmortem examination confirmed the hepatosplenomegaly with marked sinusoidal hemophagocytosis, along with striking hemophagocytosis in the bone marrow and lymph nodes. There was extensive acute and chronic ischemic bowel disease with matted bowel loops, fibrous adhesions, and patchy necrotizing enterocolitis features. Whole exome sequencing analysis demonstrated a novel mosaic heterozygous NLRC4 512 C> T (p.Ser171Phe) de novo mutation predicated to cause a dominant, gain-of-function mutation resulting in a constitutively active protein. The assembly of NLRC4-containing inflammasomes via an induced self-propagation mechanism likely enables a perpetuating process of systemic macrophage activation, presumed to be initiated in utero in this patient.