Extending the phenotype of monosomy 1p36 syndrome and mapping of a critical region for obesity and hyperphagia.

Rearrangements of 1p36 are the most frequently detected abnormalities in diagnostic testing for chromosomal cryptic imbalances and include variably sized simple terminal deletions, derivative chromosomes, interstitial deletions, and complex rearrangements. These rearrangements result in the specific pattern of malformation and neurodevelopmental disabilities that characterizes monosomy 1p36 syndrome. Thus far, no individual gene within this region has been conclusively determined to be causative of any component of the phenotype. Nor is it known if the rearrangements convey phenotypes via a haploinsufficiency mechanism or through a position effect. We have used multiplex ligation-dependent probe amplification to screen for deletions of 1p36 in a group of 154 hyperphagic and overweight/obese, PWS negative individuals, and in a separate group of 83 patients initially sent to investigate a variety of other conditions. The strategy allowed the identification and delineation of rearrangements in nine subjects with a wide spectrum of clinical presentations. Our work reinforces the association of monosomy 1p36 and obesity and hyperphagia, and further suggests that these features may be associated with non-classical manifestations of this disorder in addition to a submicroscopic deletion of approximately 2-3 Mb in size. Multiplex ligation probe amplification using the monosomy 1p36 syndrome-specific kit coupled to the subtelomeric kit is an effective approach to identify and delineate rearrangements at 1p36.

A new case of interstitial 6q16.2 deletion in a patient with Prader-Willi-like phenotype and investigation of SIM1 gene deletion in 87 patients with syndromic obesity.

The association of obesity, phenotypic abnormalities and mental retardation characterizes syndromic obesity. Its most common form is the Prader-Willi syndrome (PWS-- neonatal hypotonia, poor sucking, delayed psychomotor development, hyperphagia, severe obesity, short stature, small hands and feet, hypogonadism, mild to moderate mental retardation and behavioral disorders). A PWS-like phenotype has been described in patients with chromosome abnormalities involving the chromosome region 6q16.2 that includes the SIM1 gene. Herein we report cytogenetic and gene studies including a screening for the SIM1 gene deletion, performed on 87 patients with PWS-like phenotype, and describe the fifth case of syndromic obesity with an interstitial deletion of the chromosome segment 6q16-q21 and suggest that mutational analysis and further studies of the parental origin of chromosome alterations of 6q16.2 in patients with and without PWS-like phenotype are needed to evaluate possible imprinting effects of SIM1 gene and establish the contribution that alterations in this gene makes to the etiology of syndromic and non-syndromic obesity.

Prader-Willi-like phenotype: investigation of 1p36 deletion in 41 patients with delayed psychomotor development, hypotonia, obesity and/or hyperphagia, learning disabilities and behavioral problems.

Monosomy 1p36 is one of the most commonly observed mental retardation (MR) syndromes that results in a clinically recognizable phenotype including delayed psychomotor development and/or MR, hypotonia, epilepsy, hearing loss, growth delay, microcephaly, deep-set eyes, flat nasal bridge and pointed chin. Besides, a Prader-Willi syndrome (PWS)-like phenotype has been described in patients with 1p36 monosomy. Forty-one patients presenting hypotonia, developmental delay, obesity and/or hyperphagia and behavioral problems who tested negative for PWS were investigated by FISH and/or microsatellite markers. Twenty-six were analyzed with a 1p-specific subtelomeric probe, and one terminal deletion was identified. Thirty patients (15 of which also studied by FISH) were investigated by microsatellite markers, and no interstitial 1p36 deletion was found. Our patient presenting the 1p36 deletion did not have the striking features of this monosomy, but her clinical and behavioral features were quite similar to those observed in patients with PWS, except for the presence of normal sucking at birth. The extent of the deletion could be limited to the most terminal 2.5 Mb of 1p36, within the chromosomal region 1p36.33-1p36.32, that is smaller than usually seen in monosomy 1p36 patients. Therefore, chromosome 1p36.33 deletion should be investigated in patients with hypotonia, developmental delay, obesity and/or hyperphagia and behavioral problems who test negative for PWS.