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Cornelia de Lange Syndrome (CdLS) is a rare, dominantly inherited multisystem developmental disorder characterized by highly variable manifestations of growth and developmental delays, upper limb involvement, hypertrichosis, cardiac, gastrointestinal, craniofacial, and other systemic features. Pathogenic variants in genes encoding cohesin complex structural subunits and regulatory proteins (NIPBL, SMC1A, SMC3, HDAC8, and RAD21) are the major pathogenic contributors to CdLS. Heterozygous or hemizygous variants in the genes encoding these five proteins have been found to be contributory to CdLS, with variants in NIPBL accounting for the majority (>60%) of cases, and the only gene identified to date that results in the severe or classic form of CdLS when mutated. Pathogenic variants in cohesin genes other than NIPBL tend to result in a less severe phenotype. Causative variants in additional genes, such as ANKRD11, EP300, AFF4, TAF1, and BRD4, can cause a CdLS-like phenotype. The common role that these genes, and others, play as critical regulators of developmental transcriptional control has led to the conditions they cause being referred to as disorders of transcriptional regulation (or DTRs). Here, we report the results of a comprehensive molecular analysis in a cohort of 716 probands with typical and atypical CdLS in order to delineate the genetic contribution of causative variants in cohesin complex genes as well as novel candidate genes, genotype-phenotype correlations, and the utility of genome sequencing in understanding the mutational landscape in this population.

Cornelia de Lange syndrome (CdLS) is a multisystem genetic disorder with distinct facies, growth failure, intellectual disability, distal limb anomalies, gastrointestinal and neurological disease. Mutations in NIPBL, encoding a cohesin regulatory protein, account for >80% of cases with typical facies. Mutations in the core cohesin complex proteins, encoded by the SMC1A, SMC3 and RAD21 genes, together account for ∼5% of subjects, often with atypical CdLS features. Recently, we identified mutations in the X-linked gene HDAC8 as the cause of a small number of CdLS cases. Here, we report a cohort of 38 individuals with an emerging spectrum of features caused by HDAC8 mutations. For several individuals, the diagnosis of CdLS was not considered prior to genomic testing. Most mutations identified are missense and de novo. Many cases are heterozygous females, each with marked skewing of X-inactivation in peripheral blood DNA. We also identified eight hemizygous males who are more severely affected. The craniofacial appearance caused by HDAC8 mutations overlaps that of typical CdLS but often displays delayed anterior fontanelle closure, ocular hypertelorism, hooding of the eyelids, a broader nose and dental anomalies, which may be useful discriminating features. HDAC8 encodes the lysine deacetylase for the cohesin subunit SMC3 and analysis of the functional consequences of the missense mutations indicates that all cause a loss of enzymatic function. These data demonstrate that loss-of-function mutations in HDAC8 cause a range of overlapping human developmental phenotypes, including a phenotypically distinct subgroup of CdLS.

Objective: Netherton syndrome (NS) (OMIM:256500) is a very rare autosomal recessive multisystem disorder mostly affecting ectodermal derivatives (skin and hair) and immune system. It is caused by biallelic loss‐of‐function variants in the SPINK5 gene, encoding the protease inhibitor lymphoepithelial Kazal‐type‐related inhibitor (LEKTI). Material, Methods and Results: Here, we describe NS clinical and genetic features of homogenous patient group: 9 individuals from 7 families with similar ethnic background and who have the same SPINK5 variant (NM_006846.4: c.1048C > T, p.(Arg350*)) in homozygous or compound heterozygous states, suggesting that it is a common founder variant in Latvian population. Indeed, we were able to show that the variant is common in general Latvian population, and it shares the same haplotype among the NS individual. It is estimated that the variant arose >1000 years ago. Clinically, all nine patients exhibited typical NS skin changes (scaly erythroderma, ichthyosis linearis circumflexa, itchy skin), except for one patient who has a different skin manifestation—epidermodysplasia. Additionally, we show that developmental delay, previously underrecognized in NS, is a common feature among these patients. Conclusions: This study shows that the phenotype of NS individuals with the same genotype is highly homogeneous. [ABSTRACT FROM AUTHOR]

Kohlschütter–Tönz syndrome (KTS) is a rare, autosomal recessive syndrome characterized by a triad of epilepsy, amelogenesis imperfecta and severe global developmental delay. It was first described in a Swiss family in 1974 by Alfried Kohlschütter and Otmar Tönz. It is caused by pathogenic variants in the ROGDI gene. To the best of our knowledge, there are currently 43 patients with a confirmed ROGDI gene pathogenic variant reported. Here, we review in detail the clinical manifestations of KTS, provide an overview of all reported genetically confirmed patients, and document an additional case of KTS—a 6‐year‐old Latvian girl—with a confirmed ROGDI gene pathogenic variant. In contrast to previous reports, we detected idiopathic bilateral nephrocalcinosis in this newly identified KTS patient. Perampanel proved an effective treatment for our patient with prolonged super‐refractory status epilepticus. In order to better characterize this rare syndrome and its clinical course, it is important to report any additional symptoms and also the effectiveness of used therapies. Future research should focus on elucidating the mechanisms by which the absence/insufficiency of ROGDI‐encoded protein causes the clinical manifestations of KTS. This knowledge could shape possible ways of influencing the disease's natural history with more effective therapies. [ABSTRACT FROM AUTHOR]