The development of hindlimbs in tetrapod species relies specifically on the transcription factor TBX4. In humans, heterozygous loss-offunction TBX4 mutations cause dominant small patella syndrome (SPS) due to haploinsufficiency. Here, we characterize a striking clinical entity in four fetuses with complete posterior amelia with pelvis and pulmonary hypoplasia (PAPPA). Through exome sequencing, we find that PAPPA syndrome is caused by homozygous TBX4 inactivating mutations during embryogenesis in humans. In two consanguineous couples, we uncover distinct germline TBX4 coding mutations, p.Tyr113* and p.Tyr127Asn, that segregated with SPS in heterozygous parents and with posterior amelia with pelvis and pulmonary hypoplasia syndrome (PAPPAS) in one available homozygous fetus. A complete absence of TBX4 transcripts in this proband with biallelic p.Tyr113* stop-gain mutations revealed nonsense-mediated decay of the endogenous mRNA. CRISPR/Cas9-mediated TBX4 deletion in Xenopus embryos confirmed its restricted role during leg development. We conclude that SPS and PAPPAS are allelic diseases of TBX4 deficiency and that TBX4 is an essential transcription factor for organogenesis of the lungs, pelvis, and hindlimbs in humans.

BackgroundThe phenotypic severity of congenital muscular dystrophy-dystroglycanopathy (MDDG) syndromes associated with aberrant glycosylation of α-dystroglycan ranges from the severe Walker-Warburg syndrome or muscle-eye-brain disease to mild, late-onset, isolated limb-girdle muscular dystrophy without neural involvement. However, muscular dystrophy is invariably found across the spectrum of MDDG patients.MethodsUsing linkage mapping and whole-exome sequencing in two families with an unexplained neurodevelopmental disorder, we have identified homozygous and compound heterozygous mutations in B3GALNT2.ResultsThe first family comprises two brothers of Dutch non-consanguineous parents presenting with mild ID and behavioral problems. Immunohistochemical analysis of muscle biopsy revealed no significant aberrations, in line with the absence of a muscular phenotype in the affected siblings. The second family includes five affected individuals from an Iranian consanguineous kindred with mild-to-moderate intellectual disability (ID) and epilepsy without any notable neuroimaging, muscle, or eye abnormalities. Complementation assays of the compound heterozygous mutations identified in the two brothers had a comparable effect on the O-glycosylation of α-dystroglycan as previously reported mutations that are associated with severe muscular phenotypes.ConclusionsIn conclusion, we show that mutations in B3GALNT2 can give rise to a novel MDDG syndrome presentation, characterized by ID associated variably with seizure, but without any apparent muscular involvement. Importantly, B3GALNT2 activity does not fully correlate with the severity of the phenotype as assessed by the complementation assay.

Objective: Inborn errors of metabolism (IEMs) are disorders with various manifestations that occur mainly in the pediatric population. In countries where consanguineous marriage is common, the association between consanguinity and IEMs is highly important. No studies have been conducted in Iran examining the impact of consanguinity on IEMs. Methods: In this retrospective study, the incidences of metabolic disorders were evaluated for the years 2006 through 2016 in the North East Iran Regional Diagnostic Laboratory (Pardis Clinical and Genetic Laboratory). A total of 13,327 infants with clinical symptoms were referred and investigated for IEMs. Newborn screening was performed on samples from all patients suspected of having IEMs. Results: Of 13,327 infants examined, 60 different IEMs were diagnosed in 1,118. The most frequent disorders among our patients were glucose-6-phosphate dehydrogenase deficiency (G6PDD) (14.04%), methylmalonic and propionic acidurias (MMA/PA) (9.12%), phenylketonuria (PKU) (8%), and isovaleric acidemia (IVA) (6.98%). A significant difference was found in the prevalence of amino acid disorders between the offspring of consanguineous and those of non-consanguineous parents. No statistically significant differences were found between the 2 groups for organic or fatty acids, carnitine or urine cycles, or lysosomal storage disorders. A total of 707 of the 1,118 infants with metabolic diseases (63.24%) were children of consanguineous parents. These findings show that consanguinity can be an important factor in the inheritance of recessive mutations in a homozygous state. Conclusion: This study found a greater frequency of metabolic diseases in offspring of consanguineous parents than in those of non-consanguineous parents in a population with a high rate of consanguinity.

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Background: Janus kinase 2 (JAK2) is a tyrosine kinase located in the cytoplasm that plays a critical role in the signal transduction of cytokines and growth hormones. The conversion of valine to phenylalanine at the polypeptide position 617 results in the JAK2 (V617F) mutation, which often found in patients with myeloproliferative neoplasms (MPNs). As a result of this mutation, JAK2 is constitutively activated leading to uncontrolled cell growth. The present study aimed to investigate the frequency and relationship of the JAK2 (V617F) mutation in a population of patients with MPNs in Iran. Methods: A total of 213 patients with myeloproliferative diseases (MPDs), were included in the study. Real-time PCR was used to detect the presence of the JAK2 (V617F) mutation in the genomic DNA isolated from patient peripheral blood samples. Results: Of the 213 patients with MPDs, approximately 60 (28%) patients were positive for the JAK2 (V617F) mutation. Polycythemia Vera (PV, 42.11%) was the most common MPD, followed by Essential Thrombocythemia (ET, 29.82%), Primary Myelofibrosis (MF, 12.28%), and Chronic Myeloid Leukemia (CML, 10.5%). A significant relationship between all types of MPDs and the clinical course (p< 0.05) was observed. The relationship between age and gender among all types of MPD disease was not significant (p> 0.05). Conclusions: Of the examined cohort in North Eastern Iran, 28% of the patients with MPNs were found to have the JAK2 (V617F) mutation which determining the presence of the JAK2 (V617F) mutation helps to decide the correct form of treatment.