Midline defects in deletion 18p syndrome: clinical and molecular characterization of three patients

Copy number variation in pituitary stalk interruption syndrome: A large case series of sporadic non-syndromic patients and literature review

Abnormal hypothalamic/posterior pituitary development appears to be a major determinant of pituitary stalk interruption syndrome (PSIS). The observation of familial cases and associated congenital abnormalities suggests a genetic basis. Single-gene mutations explain less than 5% of the cases, and whole exome sequencing has shown heterogeneous results. The present study aimed to assess copy number variation (CNV) using array-based comparative genomic hybridization (aCGH) in patients with non-syndromic PSIS and comprehensively review data from the literature on CNV analysis in congenital hypopituitarism (CH) patients. Twenty-one patients with sporadic CH from our outpatient clinics presented with ectopic posterior pituitary (EPP) and no central nervous system abnormalities on magnetic resonance image (MRI) or any other malformations on physical examination at presentation were enrolled in the study. aCGH using a whole-genome customized 400K oligonucleotide platform was performed in our patients. For the literature review, we searched for case reports of patients with CH and CNV detected by either karyotype or aCGH reported in PubMed up to November 2021. Thirty-five distinct rare CNVs were observed in 18 patients (86%) and two of them (6%) were classified as pathogenic: one deletion of 1.8 Mb in chromosome 17 (17q12) and one deletion of 15 Mb in chromosome 18 (18p11.32p11.21), each one in a distinct patient. In the literature review, 67 pathogenic CNVs were published in 83 patients with CH, including the present study. Most of these patients had EPP (78% out of the 45 evaluated by sellar MRI) and were syndromic (70%). The most frequently affected chromosomes were X, 18, 20 and 1. Our study has found that CNV can be a mechanism of genetic abnormality in non-syndromic patients with CH and EPP. In future studies, one or more genes in those CNVs, both pathogenic and variant of uncertain significance, may be considered as good candidate genes.

Presentation of an Infant with Chromosome 18p Deletion Syndrome and Asymmetric Septal Hypertrophy

The frequency of 18p deletion syndrome is estimated to be ∼1/50,000 live births and is more commonly associated with certain clinical features including short stature, intellectual disability, and facial dysmorphism. Physical examination of our patient revealed a short stature, intellectual disability, facial dysmorphism (microcephaly, ptosis, epicanthus, low nasal bridge, protruding ears, long philtrum, and thin lips), and clinodactyly of the fifth finger. The peripheral karyotype was 46, XX, del (18) (p11.32p11.2). DNA microarray analysis revealed a de novo 13.9-Mb deletion at 18p11.32p.11.21. Echocardiography revealed asymmetric septal hypertrophy. Congenital cardiac abnormalities are present very rarely in this syndrome. This finding suggests that one locus or loci that play a role in cardiac development is located in this chromosomal region. Although rare, cardiac hypertrophies should be kept in mind when evaluating a patient with phenotypic anomalies and genetic results compatible with an 18p deletion syndrome.

Case report of a novel phenotype in 18q deletion syndrome

The latest decades are characterized by an enormous progression in the field of human genetics. In consequences, for various phenotypic manifestations, genetic testing could identify a specific underlying cause. An estimated incidence for all types of 18q deletions is one in 55 000 births predominant on females. About 94% of cases with 18q deletion syndrome appearance are de novo, and the remaining 6% are the inherited from a parent carrying a balanced chromosomal translocation. We present the case of a 35-year-old female who was admitted in our Unit for a second ultrasound opinion after being diagnosed at the second trimester scan at gestational age of 21 weeks of pregnancy with multiple brain and heart malformations, having the recommendation for fetal magnetic resonance imaging (MRI). Further investigations included genetic analysis and pathological examination. Major malformations diagnosed and confirmed were agenesis of the corpus callosum, ventriculomegaly with dilated fourth ventricle, partial agenesis of vermis, bilateral anophthalmia with wide nasal base and left cleft lip. Additional, cardiac malformation, with an important ventricular septal defect and overriding aorta were noted. The results of the microarray analysis showed an abnormal fetal karyotype with a loss of 30.5 basis identified in the long arm of chromosome 18. Although most of the cases of 18q deletion are sporadically or de novo, could be cases where the possible existing syndromes can be inherited from a healthy or mild affected parent. Therefore, in order to establish the recurrence risk, parental karyotypes are recommended.

Discovery of a Chinese familial deletion 18p syndrome due to a false positive result on noninvasive prenatal testing

Clinical manifestations of deletion 18p syndrome vary a lot, which makes it easily overlooked in the clinical practice. Familial transmission of deletion 18p syndrome is rare. We report a Chinese familial deletion 18p syndrome, which was diagnosed by anatomizing the underlying reason for the discrepancy between noninvasive prenatal testing (NIPT) and prenatal diagnosis. A 35-year-old pregnant woman was recruited to our center owing to the abnormal NIPT result with a high risk of chromosome 18 monosomy. However, the karyotype of the fetus was normal after amniocentesis. Further analysis indicated that the pregnant woman herself had an abnormal karyotype of 46,XX,del(18)(p11.2), (arr18p11.32p11.21[136,227-15,099,116]×1) and her first 12-year-old son had got the same deletion of 18p as her. A distinct phenotype variability was noted although they share identical deletion. We consider that adequate clinical genetic counseling is vital for women with adverse pregnancy history before getting pregnant. Maternal CNVs may be one of the main causes of the false-positive result on NIPT. NIPT, especially extended NIPT may provide extra valuable evidence when used as routine prenatal screening method.

Mosaic chromosome 18 anomaly delineated in a child with dysmorphism using a three-pronged cytogenetic techniques approach: a case report

Background

A plethora of cases are reported in the literature with iso- and ring-chromosome 18. However, co-occurrence of these two abnormalities in an individual along with a third cell line and absence of numerical anomaly is extremely rare.

Case presentation

A 7-year-old female was referred for diagnosis due to gross facial dysmorphism and severe developmental delay. She presented with dysmorphic features, hypo/hyper pigmentation of the skin, intellectual disability and craniosynostosis. G-banding chromosome analysis suggested mos 46,XX,psu idic(18)(p11.2)[25]/46,XX,r(?18)[30]. Additional analysis by molecular karyotyping suggested pure partial deletion of 15 Mb on 18p (18p11.32p11.21). Lastly, multiple rearrangements and detection of a third cell line (ring chr18 and interstitial deletion) of chr18 was observed by multi-color banding.

Conclusion

The current study presents a novel case of chromosomal abnormalities pertaining to chromosome 18 across 3 cell lines, which were delineated with a combinatorial approach of diagnostic methods.

Two Distinctively Rare Syndromes in a Case of Primary Amenorrhea: 18p Deletion and Mayer-Rokitansky-Kuster-Hauser Syndromes

Mayer-Rokitansky-Kuster-Hauser (MRKH) syndrome and 18p deletion syndrome, two genetic disorders having distinct genetic etiologies, have an exceedingly rare likelihood of coexistence. Vaginal agenesis or MRKH syndrome, the developmental failure of Mullerian ductal system-derived structures in a genotypic female fetus (46, XX), leads to congenital absence of uterus and vagina in variable degree. The 18p deletion syndrome is a rare chromosomal disorder, characterized by dysmorphic features, stunted growth, and mental retardation, which is caused by deletion of a part or all of the short arm of chromosome 18. A detailed evaluation of primary amenorrhea in a 16-year-old girl yielded both MRKH syndrome and 18p deletion syndrome. Extensive literature search could not identify any reported case bearing this combination of syndromes. This case presentation and review emphasizes on the importance of karyotyping in MRKH patients having atypical features.

Prenatal diagnosis of de novo monosomy 18p deletion syndrome by chromosome microarray analysis: Three case reports

RATIONALE

Monosomy 18p deletion syndrome refers to a rare chromosomal disorder resulting from the part deletion of the short arm of chromosome 18. Prenatal diagnosis of de novo 18p deletion syndrome is a challenge due to its low incidence and untypical prenatal clinical presentation.

PATIENT CONCERNS

Three cases received amniocentesis due to increased nuchal translucency (INT), high risk for Down syndrome, and INT combined intrauterine growth retardation (IUGR), respectively.

DIAGNOSIS

The 3 cases were diagnosed with de novo monosomy 18p deletion syndrome by amniocentesis and chromosome microarray analysis (CMA).

INTERVENTIONS

Karyotype analysis and CMA were used to analyze the abnormal chromosome.

OUTCOMES

Case 1 and case 2 revealed 13.87 and 12.68 Mb deletions by array-CGH analysis, respectively. Case 3 revealed 6.9 Mb deletions in 18p11.32p11.31 and 7.5 Mb deletions in 18p11.23p11.21 by single nucleotide polymorphism array. All of the pregnancies were terminated due to the abnormal chromosome.

LESSONS

The fetal phenotype of monosomy 18p deletion syndrome shows great variability and may not be evident during the pregnancy. CMA may be served as an effective tool for the diagnosis of prenatal monosomy 18p deletion syndrome diagnosis.

Syndromes associated with holoprosencephaly

Holoprosencephaly (HPE) is partial or complete failure of the forebrain to divide into hemispheres and can be an isolated finding or associated with a syndrome. Most cases of HPE are associated with a syndrome and roughly 40%-60% of fetuses with HPE have trisomy 13 which is the most common etiology of HPE. Other syndromes associated with HPE include additional aneuploidies like trisomy 18 and single gene disorders such as Smith-Lemli-Opitz syndrome. There are a number of syndromes such as pseudotrisomy 13 which do not have a known molecular etiology; therefore, this review has two parts: syndromes with a molecular diagnosis and syndromes where the etiology is yet to be found. As most HPE is syndromic, this review provides a comprehensive list and description of syndromes associated with HPE that may be used as a differential diagnosis and starting point for evaluating individuals with HPE.

A case of 18p deletion syndrome after blepharoplasty

Objective

The deletion of the short arm of chromosome 18 is thought to be one of the rare chromosomal aberrations. Here, we report a case to review this disease.

Case report

The proband is a five-and-a-half-year-old girl who has had phenotypes manifested mainly by ptosis, broad face, broad neck with low posterior hairline, mental retardation, short stature, and other malformations. Chromosomal analysis for her mother showed a normal karyotype. Her father and younger brother were phenotypically normal.

Result

Phenotypical features were quite similar throughout other cases and in accordance with the usual phenotype of del(18p) suggested within the same cases and among the del(18p) cases described. She underwent blepharoplasty, which improved her appearance.

Conclusion

18p deletion syndrome is diagnosed by gene analysis. Plastic surgeries for improving the appearance might be an option for these patients.

A 18p11.23-p11.31 microduplication in a boy with psychomotor delay, cerebellar vermis hypoplasia, chorioretinal coloboma, deafness and GH deficiency

Background

Rearrangements involving the short arm of chromosome 18 have been extensively described. Here we report a microduplication of 320.5–431.5 Kb at 18p11.31-p11.23 in a 10 year-old boy.

Case presentation

In a 10 year-old boy with moderate psychomotor delay, hypoplasia of the cerebellar vermis, chorioretinal coloboma, deafness and growth hormone deficiency (GHD), an interstitial microduplication at 18p11.31-p11.23 was identified by array-CGH. This maternally inherited microduplication, encompasses three genes, namely ARHGAP28, LINC00668 and LAMA1 (a gene involved in cerebellum and retinal development).

Conclusions

The genotype-phenotype is discussed with particular attention to the LAMA1 gene, although it is difficult, as in many other similar situations, to assess the causality of the detected duplication in the absence of further studies aiming to explore the presence of co-occurring variants that could explain the incomplete penetrance.

Electronic supplementary material

The online version of this article (doi:10.1186/s13039-016-0298-9) contains supplementary material, which is available to authorized users.

Retrospective karyotype study in mentally retarded patients

OBJECTIVE

To describe the chromosomal alterations in patients with mental retardation (MR) using G-banding karyotype analysis.

METHOD

A retrospective study of the results G-banding karyotype analysis of 369 patients investigated for MR was performed. Based on the structural rearrangements found, the authors searched all chromosomal regions related with breakpoints, and these were compared with the literature on MR and databases.

RESULTS

338 (91.6%) normal cases, and 31 (8.4%) with some type of chromosomal abnormality were identified. Among the altered cases, 21 patients (67.8%) were identified with structural chromosomal alterations, nine (29%) with numerical alterations, and one (3.2%) with numerical and structural alterations.

CONCLUSION

Structural chromosomal abnormalities were observed more frequently in this study. G-banding karyotyping contributes to the investigation of the causes of MR, showing that this technique can be useful for initial screening of patients. However, higher resolution techniques such as array based comparative genomic hybridization (aCGH) and multiplex ligation-dependent probe amplification (MPLA) can detect submicroscopic alterations commonly associated with MR.

A French Approach to Test Fetuses with Ultrasound Abnormalities Using a Customized Microarray as First-Tier Genetic Test

Cytogenetic microarray analysis is now the first-tier genetic test used in a postnatal clinical setting to explore genomic imbalances in individuals with developmental disability and/or birth defects. However, in a prenatal setting, this technique is not widely implemented, largely because the clinical impact of some copy number variants (CNVs) remains difficult to assess. This limitation is especially true in France where termination of pregnancy for medical reasons may be performed at any stage of gestation. During a period of 15 months, we investigated 382 fetuses presenting with ultrasound anomalies, using a customized microarray designed to avoid the detection of CNVs raising challenges for genetic counseling. After excluding common aneuploidies, 20/374 (5.3%) fetuses had a pathogenic CNV, among which 12/374 (3.2%) could have been detected by karyotyping, whereas 8/374 (2.1%) were cryptic. Within these 374 cases, 300 were ongoing pregnancies at the time of array comparative genomic hybridization (aCGH) testing. For these pregnancies, we detected 18/300 (6%) pathogenic CNVs, among which 6/300 (2%) were cryptic. Using this approach, only 2/300 (0.6%) of the detected CNVs raised difficulties for genetic counseling. This study confirms the added value of this strategy in a prenatal clinical setting to minimize ethical issues for genetic counseling while enhancing the detection of genomic imbalances.

Whole arm deletions of 18p: medical and developmental effects

Deletions of the short arm of chromosome 18 have been well-described in case reports. However, the utility of these descriptions in clinical practice is limited by varied and imprecise breakpoints. As we work to establish genotype-phenotype correlations for 18p-, it is critical to have accurate and complete clinical descriptions of individuals with differing breakpoints. In addition, the developmental profile of 18p- has not been well-delineated. We undertook a thorough review of the medical histories of 31 individuals with 18p- and a breakpoint in the centromeric region. We collected developmental data using mailed surveys and questionnaires. The most common findings included neonatal complications; cardiac anomalies; hypotonia; MRI abnormalities; endocrine dysfunction; strabismus; ptosis; and refractive errors. Less common features included holoprosencephaly and its microforms; hearing loss; and orthopedic anomalies. The developmental effects of the deletion appear to be less severe than reported in the literature, as average IQ scores were in the range of borderline intellectual functioning. Based on responses to standardized questionnaires, it appears this population has marked difficulty with activities of daily living, though several young adults were able to live independent of their parents. This manuscript represents the most comprehensive description of a cohort of 18p- individuals with identical breakpoints. Despite identical breakpoints, a great deal of phenotype variability remained among this population, suggesting that many of the genes on 18p- cause low-penetrance phenotypes when present in a hemizygous state. Future efforts will focus on the clinical description of individuals with more distal breakpoints and the identification of critical regions and candidate genes.

Adults with Chromosome 18 Abnormalities

The identification of an underlying chromosome abnormality frequently marks the endpoint of a diagnostic odyssey. However, families are frequently left with more questions than answers as they consider their child's future. In the case of rare chromosome conditions, a lack of longitudinal data often makes it difficult to provide anticipatory guidance to these families. The objective of this study is to describe the lifespan, educational attainment, living situation, and behavioral phenotype of adults with chromosome 18 abnormalities. The Chromosome 18 Clinical Research Center has enrolled 483 individuals with one of the following conditions: 18q-, 18p-, Tetrasomy 18p, and Ring 18. As a part of the ongoing longitudinal study, we collect data on living arrangements, educational level attained, and employment status as well as data on executive functioning and behavioral skills on an annual basis. Within our cohort, 28 of the 483 participants have died, the majority of whom have deletions encompassing the TCF4 gene or who have unbalanced rearrangement involving other chromosomes. Data regarding the cause of and age at death are presented. We also report on the living situation, educational attainment, and behavioral phenotype of the 151 participants over the age of 18. In general, educational level is higher for people with all these conditions than implied by the early literature, including some that received post-high school education. In addition, some individuals are able to live independently, though at this point they represent a minority of patients. Data on executive function and behavioral phenotype are also presented. Taken together, these data provide insight into the long-term outcome for individuals with a chromosome 18 condition. This information is critical in counseling families on the range of potential outcomes for their child.

Neuropsychological function in a child with 18p deletion syndrome: a case report

We report the neuropsychological profile of a 4-year-old boy with the rare 18p deletion syndrome. We used a battery of standardized tests to assess his development in intellect, language, visuomotor integration, academic readiness, socialization, and emotional and behavioral health. The results showed borderline intellectual function except for low average nonverbal reasoning skills. He had stronger receptive than expressive language skills, although both were well below his age group. He had impaired visuomotor integration and pre-academic skills such as letter identification. Emotional and behavioral findings indicated mild aggressiveness, anxiety, low frustration tolerance, and executive function weaknesses, especially at home. Interestingly, he showed social strengths, responding to joint attention and sharing enjoyment with his examiner. With its assessment of development in many domains, this case report is among the first to characterize the neuropsychological and psychiatric function of a young child with 18p deletion syndrome. We discuss the implications of our findings for clinical practice.

Dicentric Chromosome 14;18 Plus Two Additional CNVs in a Girl with Microform Holoprosencephaly and Turner Stigmata

We report a 20-year-old female with features evocative of Turner syndrome (short stature, broad trunk, mild webbed neck), dysmorphic face, minor features of holo-prosencephaly (HPE), small hands and feet, excessive hair growth on anterior trunk and intellectual disability. Cytogenetic analysis identified a pseudodicentric 14;18 chromosome. Genome wide single nucleotide polymorphism (SNP) array showed a terminal deletion of approximately 10.24 Mb, from 18p11.32 to 18p11.22, flanked by a duplication of approximately 1.15 Mb, from 18p11.22 to 18p11.21. In addition, the SNP array revealed a duplication of 516 kb in 16p11.2. We correlated the patient’s clinical findings with the features mentioned in the literature for these copy number variations. This case study shows the importance of microarray analysis in the detection of cryptic chromosomal rearrangements in patients with intellectual disability and multiple congenital anomalies.

Chromosome 18p deletion syndrome presenting holoprosencephaly and premaxillary agenesis: prenatal diagnosis and aCGH characterization using uncultured amniocytes

We present prenatal diagnosis of a de novo distal 18p deletion involving 14.06Mb at 18p11.32-p11.21 by aCGH using uncultured amniocytes in a pregnancy with fetal holoprosencephaly and premaxillary agenesis. QF-PCR analysis showed that distal 18p deletion was from maternal origin. Metaphase FISH analysis confirmed haploinsufficiency of TGIF. We discuss the functions of the genes that are deleted within this region. The present case shows the usefulness of applying aCGH on uncultured amniocytes for rapid aneuploidy diagnosis in cases with prenatally detected fetal structural abnormalities.

Pituitary stalk interruption syndrome and isolated pituitary hypoplasia may be caused by mutations in holoprosencephaly-related genes

CONTEXT

Holoprosencephaly (HPE) is a developmental defect characterized by wide phenotypic variability, ranging from minor midline malformations (eg, single central incisor) to severe deformities. In 10-15% of HPE patients, mutations in specific genes have been identified (eg, SHH, TGIF, SIX3). Pituitary stalk interruption syndrome (PSIS) constitutes a distinct abnormality of unknown pathogenesis, whereas isolated pituitary hypoplasia (IPH) has been linked to various developmental genes.

OBJECTIVE

Three of our patients with PSIS had a single central incisor, a malformation encountered in some HPE cases. Based on this observation, we initiated a search for mutations in HPE-associated genes in 30 patients with PSIS or IPH.

DESIGN AND PARTICIPANTS

The entire coding region of the TGIF, SHH, and SIX3 genes was sequenced in patients with combined pituitary hormone deficiency associated with either PSIS or IPH and in healthy controls.

RESULTS

Two novel mutations in the HPE-related genes were detected (ie, c.799 C>T, p.Q267X in the TGIF gene, and c.1279G>A, p.G427R in the SHH gene) in 2 of our patients. The overall incidence of HPE-related gene mutations in our nonsyndromic and nonchromosomal patients was 6.6%. No molecular defect in the SIX3 gene was detected in our cohort.

CONCLUSIONS

The data suggest that HPE-related gene mutations are implicated in the etiology of isolated pituitary defects (PSIS or IPH). Alternatively, PSIS or IPH may constitute mild forms of an expanded HPE spectrum.

Prenatal diagnosis of alobar holoprosencephaly, cyclopia, proboscis, and isochromosome 18q in the second trimester

We would like to present a rare case of alobar holoprosencephaly (HPE) in a fetus diagnosed by routine sonography in the second trimester. Structural sonography demonstrated multiple facial anomalies including absent nasal bone, flat facial profile, hypotelorism, fusion of the orbits and proboscis. After counseling, termination of pregnancy was performed by vaginally administered misoprostol. Karyotyping of amniotic fluid cells revealed an isochromosome 18q, resulting in a trisomy 18q and monosomy 18p. A stillborn female of 390 g with several congenital anomalies was born. Postmortem examination demonstrated several anomalies including the HPE, cyclopia, double fused eye, absence of the nose, and the presence of a proboscis. In the literature only a few cases have been published.

Mosaic ring chromosome 18, ring chromosome 18 duplication/deletion and disomy 18: perinatal findings and molecular cytogenetic characterization by fluorescence in situ hybridization and array comparative genomic hybridization

OBJECTIVE

To present the perinatal findings and molecular cytogenetic analysis of a rare chromosomal abnormality involving structural and numerical abnormalities of chromosome 18.

MATERIALS, METHODS AND RESULTS

A 36-year-old woman, gravida 5, para 3, underwent amniocentesis because of her advanced maternal age. Amniocentesis revealed a karyotype of 46,XY,r(18) [27]/45,XY,-18[5]/46,XY[5]. The parents decided to continue the pregnancy. Level II ultrasound revealed ventriculomegaly. At 38 weeks of gestation, a 3,725 g male fetus was delivered. The fetus had microcephaly, hypertelorism, epicanthal folds, cleft palate, a broad flat nose, simian creases, broad hands, tapered fingers, clubfeet, micropenis, a sacral dimple, hypotonia, ventriculomegaly, and a ventricular septal defect. The peripheral blood lymphocytes revealed a karyotype of 46,XY,r(18)[81]/45,XY,-18[3]/46,XY,idic r(18)[3]/46,XY[13]. Fluorescence in situ hybridization using chromosome 18 centromeric probe (cep18) and subtelomeric (18pter, 18qter) identified four types of cells, r(18), idic r(18), monosomy 18, and disomy 18. Array comparative genomic hybridization analysis of the blood demonstrated a 14.9-Mb deletion at chromosome 18p [arr cgh 18p11.32p11.21 (0-14,941,330)× 1] and a 29.6-Mb deletion at chromosome 18q [arr cgh 18q21.2q23 (46,533,430-76,117,153) × 1]. The proband's karyotype was 46,XY,r(18)(p11.21q21.2)[81]/45,XY,-18[3]/46,XY,idic r(18)(p11.21q21.2;p11.21q21.2)[3]/46,XY[13].

CONCLUSION

Array comparative genomic hybridization is useful to determine the breakpoints of a ring chromosome, particularly in cases where the ring chromosome comprises the majority of the mosaicism.

Monosomy 18p presenting with holoprosencephaly and increased nuchal translucency in the first trimester: report of 2 cases

OBJECTIVE

The purpose of this series is to describe the first-trimester sonographic findings leading to the diagnosis of monosomy 18p.

METHODS

The sonographic appearance of 2 cases of monosomy 18p, detected as part of first-trimester sonographic screening for aneuploidy at this institution, was reviewed.

RESULTS

Increased nuchal translucency thickness, alobar holoprosencephaly, and facial defects were detected in both cases. Chromosomal analysis by chorionic villus sampling revealed de novo del(18p) in 1 case and monosomy 18p as the result of an 18q isochromosome in the other.

CONCLUSIONS

Increased nuchal translucency thickness in association with brain and face anomalies on a first-trimester scan allowed the early diagnosis of monosomy 18p. Fetuses with holoprosencephaly can be readily identified in the first trimester by examining a cross section of the fetal head looking for the "butterfly" sign. Prenatal karyotyping provides important information regarding the etiology and risk of recurrence in these cases.

Monosomy 18p

Monosomy 18p refers to a chromosomal disorder resulting from the deletion of all or part of the short arm of chromosome 18. The incidence is estimated to be about 1:50,000 live-born infants. In the commonest form of the disorder, the dysmorphic syndrome is very moderate and non-specific. The main clinical features are short stature, round face with short philtrum, palpebral ptosis and large ears with detached pinnae. Intellectual deficiency is mild to moderate. A small subset of patients, about 10–15 percent of cases, present with severe brain/facial malformations evocative of holoprosencephaly spectrum disorders. In two-thirds of the cases, the 18p- syndrome is due to a mere terminal deletion occurring de novo, in one-third the following are possible: a de novo translocation with loss of 18p, malsegregation of a parental translocation or inversion, or a ring chr18. Parental transmission of the 18p- syndrome has been reported. Cytogenetic analysis is necessary to make a definite diagnosis. Recurrence risk for siblings is low in de novo deletions and translocations, but is significant if a parental rearrangement is present. Deletion 18p can be detected prenatally by amniocentesis or chorionic villus sampling and cytogenetic testing. Differential diagnosis may include a wide number of syndromes with short stature and mild intellectual deficiency. In young children, deletion 18p syndrome may be vaguely evocative of either Turner syndrome or trisomy 21. No specific treatment exists but speech therapy and early educational programs may help to improve the performances of the children. Except for the patients with severe brain malformations, the life expectancy does not seem significantly reduced.