Dopamine transporter deficiency syndrome is an SLC6A3-related progressive infantile-onset parkinsonism-dystonia that mimics cerebral palsy. Ng et al. describe clinical features and molecular findings in a new cohort of patients. They report infants with classical disease, as well as young adults manifesting as atypical juvenile-onset parkinsonism-dystonia, thereby expanding the disease spectrum.

Epileptic encephalopathies are genetically heterogeneous severe disorders in which epileptic activity contributes to neurological deterioration. We studied two unrelated children presenting with a distinctive early-onset epileptic encephalopathy characterized by refractory epilepsy and absent developmental milestones, as well as thick and short corpus callosum and persistent cavum septum pellucidum on brain MRI. Using whole-exome sequencing, we identified biallelic mutations in seizure threshold 2 (SZT2) in both affected children. The causative mutations include a homozygous nonsense mutation and a nonsense mutation together with an exonic splice-site mutation in a compound-heterozygous state. The latter mutation leads to exon skipping and premature termination of translation, as shown by RT-PCR in blood RNA of the affected boy. Thus, all three mutations are predicted to result in nonsense-mediated mRNA decay and/or premature protein truncation and thereby loss of SZT2 function. Although the molecular role of the peroxisomal protein SZT2 in neuronal excitability and brain development remains to be defined, Szt2 has been shown to influence seizure threshold and epileptogenesis in mice, consistent with our findings in humans. We conclude that mutations in SZT2 cause a severe type of autosomal-recessive infantile encephalopathy with intractable seizures and distinct neuroradiological anomalies.

By using homozygosity mapping in a consanguineous Pakistani family, we detected linkage of nonsyndromic hearing loss to a 7.6 Mb region on chromosome 3q13.31-q21.1 within the previously reported DFNB42 locus. Subsequent candidate gene sequencing identified a homozygous nonsense mutation (c.1135G>T [p.Glu379X]) in ILDR1 as the cause of hearing impairment. By analyzing additional consanguineous families with homozygosity at this locus, we detected ILDR1 mutations in the affected individuals of 10 more families from Pakistan and Iran. The identified ILDR1 variants include missense, nonsense, frameshift, and splice-site mutations as well as a start codon mutation in the family that originally defined the DFNB42 locus. ILDR1 encodes the evolutionarily conserved immunoglobulin-like domain containing receptor 1, a putative transmembrane receptor of unknown function. In situ hybridization detected expression of Ildr1, the murine ortholog, early in development in the vestibule and in hair cells and supporting cells of the cochlea. Expression in hair cell- and supporting cell-containing neurosensory organs is conserved in the zebrafish, in which the ildr1 ortholog is prominently expressed in the developing ear and neuromasts of the lateral line. These data identify loss-of-function mutations of ILDR1, a gene with a conserved expression pattern pointing to a conserved function in hearing in vertebrates, as underlying nonsyndromic prelingual sensorineural hearing impairment.

The CRISPR/Cas technology enables targeted genome editing and the rapid generation of transgenic animal models for the study of human genetic disorders. Here we describe an autosomal recessive human disease in two unrelated families characterized by a split-foot defect, nail abnormalities of the hands, and hearing loss, due to mutations disrupting the SAM domain of the protein kinase ZAK. ZAK is a member of the MAPKKK family with no known role in limb development. We show that Zak is expressed in the developing limbs and that a CRISPR/Cas-mediated knockout of the two Zak isoforms is embryonically lethal in mice. In contrast, a deletion of the SAM domain induces a complex hindlimb defect associated with down-regulation of Trp63, a known split-hand/split-foot malformation disease gene. Our results identify ZAK as a key player in mammalian limb patterning and demonstrate the rapid utility of CRISPR/Cas genome editing to assign causality to human mutations in the mouse in <10 wk.

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The Say-Barber/Biesecker/Young-Simpson (SBBYS) type of the blepharophimosis-mental retardation syndrome group (Ohdo-like syndromes) is a multiple congenital malformation syndrome characterized by vertical narrowing and shortening of the palpebral fissures, ptosis, intellectual disability, hypothyroidism, hearing impairment, and dental anomalies. Mutations of the gene encoding the histone-acetyltransferase KAT6B have been recently identified in individuals affected by SBBYS syndrome. SBBYS syndrome-causing KAT6B mutations cluster in a ~1,700 basepair region in the 3' part of the large exon 18, while mutations located in the 5' region of the same exon have recently been identified to cause the genitopatellar syndrome (GPS), a clinically distinct although partially overlapping malformation-intellectual disability syndrome. Here, we present two children with clinical features of SBBYS syndrome and de novo truncating KAT6B mutations, including a boy who was diagnosed at the age of 4 months. Our results confirm the implication of KAT6B mutations in typical SBBYS syndrome and emphasize the importance of genotype-phenotype correlations at the KAT6B locus where mutations truncating the KAT6B protein at the amino-acid positions ~1,350-1,920 cause SBBYS syndrome.

Mutations in IRF6 cause Van der Woude syndrome (VWS), one of the most common syndromes associated with cleft lip (CL) with or without cleft palate (CP). The presence of pits on the lower lip of patients is the most characteristic feature of the syndrome. We have identified three novel and seven previously reported IRF6 mutations in 12 of 16 unrelated families segregating VWS from Pakistan. The three newly identified mutations include a frameshift (c.568delG) and two missense mutations c.295G>A (p.G99S) and c.1219T>C (p.S407P). Recent functional studies on IRF6 and the three-dimensional structure of IRF5 carboxy (C) terminus, a protein encoded by a paralog of IRF6, shed light on the p.S407P substitution. Additionally, the identification of the same mutations responsible for VWS in Pakistan, as reported in other global populations worldwide, marks these residues as mutational hotspots and indicates their essential role in structural stability or function of IRF6. This is the first study of VWS in Pakistan and we estimate that 1 in 100 patients with CL with or without CP (CL/P) are affected in the Pakistani population predominantly from the Punjab area.

A molecular study was conducted to investigate the prevalence of Hepatitis C virus genotypes in HCV infected population of Balochistan. Forty HCV seropositive samples belonging to seven different locations of Balochistan were collected from different health care centres. Qualitative analysis of these samples using PCR resulted in 28 positive samples. The PCR positive samples were subjected to genotyping using the method described by Ohno et al (J Clin Microbiol 35:201-202, 1997) with minor modifications. Genotyping of 28 samples revealed three different genotypes including 3a, 3b and 1a. The most prevalent genotype was 3a with rate of 50% followed by genotype 3b and 1a, respectively. Nine samples remained untyped, suggesting the need of further investigation of genotypes in this region. It has been proposed that sequencing of these samples may be helpful to unreveal these genotypes and further epidemiology of HCV genotypes. Further more, extensive and large scale studies are needed to understand the epidemiology of HCV genotypes, as no such study has been carried in this province.