Pallister-Killian syndrome: a study of 22 British patients.

BACKGROUND: Pallister-Killian syndrome is a rare, sporadic condition caused by mosaic tetrasomy of the short arm of chromosome 12 (12p). The main features are intellectual disability, seizures, dysmorphic features and a variety of congenital malformations. Most available information comes from individual case reports. We report the results of a British study into Pallister-Killian syndrome, which is the first to provide comprehensive data on a population-based sample. METHOD: A detailed phenotypical study was carried out in Great Britain. All individuals with Pallister-Killian syndrome were eligible to participate. Each participant underwent a structured history, developmental assessment and clinical examination. Buccal mucosal samples were analysed by interphase fluorescence in situ hybridization (FISH) and blood samples by array comparative genomic hybridization (CGH). Genotype-phenotype correlations were sought in these tissues and existing skin biopsy reports. RESULTS: Twenty-two patients with Pallister-Killian syndrome, ranging from 4 months to 31 years were recruited and comprehensive data on each obtained. The birth incidence was 5.1 per million live births. Array CGH only suggested the diagnosis in 15.8% but buccal FISH could have made the diagnosis in 75.0%. There was no genotype-phenotype correlation in any of the tissues studied. This study shows that the high birth weights and profound intellectual disability classically described in Pallister-Killian syndrome are not universal. Mild or moderate intellectual disability was present in 27.6% of this cohort and all birth weights were within 2.67SD of the mean. New features which have not previously been recognised as part of Pallister-Killian syndrome include anhydrosis/hypohydrosis and episodic hyperventilation, suggesting involvement of the autonomic system.

Disruption of AP3B1 by a chromosome 5 inversion: a new disease mechanism in Hermansky-Pudlak syndrome type 2.

BACKGROUND: Hermansky-Pudlak syndrome 2 (HPS2; OMIM #608233) is a rare, autosomal recessive disorder caused by loss-of-function genetic variations affecting AP3B1, which encodes the ß3A subunit of the adaptor-related protein complex 3 (AP3). Phenotypic characteristics include reduced pigmentation, absent platelet dense granule secretion, neutropenia and reduced cytotoxic T lymphocyte (CTL) and natural killer (NK) cell function. To date HPS2 has been associated with non-synonymous, stop-gain or deletion-insertion nucleotide variations within the coding region of AP3B1. CASE PRESENTATION: We describe a consanguineous female infant with reduced pigmentation, neutropenia and recurrent infections. Platelets displayed reduced aggregation and absent ATP secretion in response to collagen and ADP, indicating a platelet dense granule defect. There was increased basal surface expression of CD107a (lysosome-associated membrane protein 1(LAMP-1)) on NK cells and CTLs from the study subject and a smaller increase in the percentage of CD107a positive cells after stimulation compared to most healthy controls. Immunoblotting of protein extracts from EBV-transformed lymphoblasts from the index case showed absent expression of full-length AP-3 ß3A subunit protein, confirming a phenotypic diagnosis of HPS2.The index case displayed a homozygous pericentric inv(5)(p15.1q14.1), which was also detected as a heterozygous defect in both parents of the index case. No loss of genetic material was demonstrated by microarray comparative genome hybridisation at 60kb resolution. Fluorescence in-situ hybridisation using the 189.6kb probe RP11-422I12, which maps to 5q14.1, demonstrated dual hybridisation to both 5q14.1 and 5p15.1 regions of the inverted Chr5. The RP11-422I12 probe maps from intron 1 to intron 16 of AP3B1, thus localising the 5q inversion breakpoint to within AP3B1. The probe RP11-211K15, which corresponds to an intergenic region on 5p also showed dual hybridisation, enabling localisation of the 5p inversion breakpoint. CONCLUSION: This case report extends the phenotypic description of the very rare disorder HPS2. Our demonstration of a homozygous Chr5 inversion predicted to disrupt AP3B1 gene provides a novel pathogenic mechanism for this disorder.

16p11.2-p12.2 duplication syndrome; a genomic condition differentiated from euchromatic variation of 16p11.2.

Chromosome 16 contains multiple copy number variations (CNVs) that predispose to genomic disorders. Here, we differentiate pathogenic duplications of 16p11.2-p12.2 from microscopically similar euchromatic variants of 16p11.2. Patient 1 was a girl of 18 with autism, moderate intellectual disability, behavioural difficulties, dysmorphic features and a 7.71-Mb (megabase pair) duplication (16:21 521 005-29 233 146). Patient 2 had a 7.81-Mb duplication (16:21 382 561-29 191 527), speech delay and obsessional behaviour as a boy and, as an adult, short stature, macrocephaly and mild dysmorphism. The duplications contain 65 coding genes of which Polo-like kinase 1 (PLK1) has the highest likelihood of being haploinsufficient and, by implication, a triplosensitive gene. An additional 1.11-Mb CNV of 10q11.21 in Patient 1 was a possible modifier containing the G-protein-regulated inducer of neurite growth 2 (GPRIN2) gene. In contrast, the euchromatic variants in Patients 3 and 4 were amplifications from a 945-kb region containing non-functional immunoglobulin heavy chain (IGHV), hect domain pseudogene (HERC2P4) and TP53-inducible target gene 3 (TP53TG3) loci in proximal 16p11.2 (16:31 953 353-32 898 635). Paralogous pyrosequencing gave a total copy number of 3-8 in controls and 8 to >10 in Patients 3 and 4. The 16p11.2-p12.2 duplication syndrome is a recurrent genomic disorder with a variable phenotype including developmental delay, dysmorphic features, mild to severe intellectual disability, autism, obsessive or stereotyped behaviour, short stature and anomalies of the hands and fingers. It is important to differentiate pathogenic 16p11.2-p12.2 duplications from harmless, microscopically similar euchromatic variants of proximal 16p11.2, especially at prenatal diagnosis.

A 2.3Mb deletion of 17q24.2-q24.3 associated with 'Carney Complex plus'.

We present a 12-year-old with a de novo interstitial deletion of approximately 2.3Mb in chromosome band 17q24.2-q24.3, which was identified by array CGH. The most characteristic features in this case are posterior laryngeal cleft and the presence of numerous freckles and lentigines in childhood. Growth restriction, microcephaly and moderate mental retardation are also prominent features but are frequently seen with other chromosomal anomalies. The microdeletion causes haploinsufficiency of PRKAR1A (protein kinase, cAMP-dependent, regulatory 1alpha), which is known to cause Carney Complex but this diagnosis alone does not account for all of her problems and she therefore has 'Carney Complex plus'. This report illustrates the practical benefits associated with a clear cytogenetic diagnosis, as regular endocrinological and cardiac screening is required.

SHOX mutations in a family and a fetus with Langer mesomelic dwarfism.

Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia (LMD) are caused by mutations in the SHOX gene. LWD results from haploinsufficiency and is dominantly inherited, while the more severe LMD results from the homozygous loss of SHOX. We describe a family and fetus with two SHOX mutations. Several relatives carry an approximately 200 kb interstitial deletion that includes the whole SHOX gene. Their condition is mild, with no Madelung deformity, and was originally diagnosed as hypochondroplasia (HCH). This deletion was also transmitted to a female fetus. However, unlike her carrier relatives, the ultrasound scan of the fetus and subsequent autopsy were consistent with LMD. The fetus inherited an additional Xp deletion (Xpter-Xp22.12) that also included the SHOX gene from her chromosomally normal father. This represents a unique molecular condition for LMD: the fetus is a compound heterozygote with two independent deletions, one inherited and one arising from a de novo event.