Kabuki syndrome. Kabuki syndrome (KS) is a congenital mental retardation syndrome with additional multisystemic involvement. Major features include long palpebral fissures, short nasal septum, arched eyebrows, depressed nasal tip, high-arched palate, prominent ears, persistent fingertip pad and short 5th digit, hypotonia, short stature and IQ <80. Cardiovascular defects, vertebral deformities, hip dislocation, urinary tract malformations, hearing loss and seizures have been reported as minor features. Liver involvement includes high GGT cholangiopathy, BA (xxx Xxxxxx et al. 2000) and end stage liver disease leading to LT (Xxxxx-Xxxxxx et al. 1998). The incidence is 1/32,000; it is sporadic with an equal sex ratio (Xxxxxxx et al. 1981). In 2010, whole exome sequencing (XXX) of 10 unrelated patients with KS, 7 of European ancestry, 2 of Hispanic ancestry and 1 of mixed European and Haitian ancestry, identified nonsense or frameshift mutations in the MLL2 gene in 7 patients. Follow-up Sanger sequencing detected mutations in MLL2 on chromosome 12q12-14 in 2 of the 3 remaining individuals with KS and in 26 of 43 additional cases. In all, 33 distinct MLL2 mutations were identified in 35 of 53 families (66%) with KS (Xx et al. 2010). Currently over 247 mutations have been identified with a high incidence of de novo occurrence (Xxxxxxxx et al. 2011). In about 10% of KS patients, mutations in Lysine-specific demethylase 6a gene (KDM6A) have been found (Xxxxxxx et al. 2012). The syndrome, including clinical features and causative genes will be discussed separately at length in section 4.1.
Kabuki syndrome. Bi-directional fluorescent DNA sequencing (BigDye v3.1) was utilized in screening for mutations in exons 1-54 of the MLL2 and 1-29 of KDM6A genes, in the no MLL2 mutations patients. Large deletions and duplications in both genes were tested by multiplex ligation- dependent probe amplification (MLPA). Genetic analysis was undertaken in the Genomics Diagnostic Laboratory, Manchester. Each patient was found to be heterozygous for different MLL2 mutations (Table 23). Patients 1, 2 and 4 had nonsense truncating mutations identified. The mutation was novel in patient 2. Parental DNA was not tested. In patient 3, a heterozygous splice site mutation of the MLL2 gene was revealed, previously reported in dbSNP. As the diagnostic laboratory suspected that this mutation was a neutral polymorphism, DNA was also sequenced for KDM6A mutations for exons 1-29. No pathogenic mutations were identified. Following MLPA dosage analysis no evidence of any large deletion or duplication affecting the KDM6A exons was detected. Maternal DNA proved negative for mutations in KDM6A and also for the MLL2 c.5868-8C>T variant identified in the index case. Paternal DNA was not available to determine the inheritance of the MLL2 variant and also confirm its clinical significance. Screening of patient’s 4 DNA revealed a heterozygous nonsense mutation in exon 10 of the MLL2 gene. Paternal DNA proved negative for this MLL2 mutation. 1 c.9961C>T R3312* Truncating Ng et al.
