Maternal effects in human cleft lip and palate.

To look for a persistent maternal effect of CL(P) and CP, 8,000 pedigrees were screened for half sibships, and data were pooled from 16 investigators. After excluding known genetic or cytogenetic diagnoses from the probands with facial clefts, a recurrence risk of .011 was obtained for CL(P) based upon 342 maternal half sibs. This was nearly identical to the risk of .014 based upon 210 paternal half sibs. CP proband frequencies of .004 for maternal half sibs and .009 for the paternal counterparts were also found. The lack of significant maternal effects in this data supports previously reported data from twin studies and from interracial crosses from Hawaii. The lack of maternal effect in human CL(P) and CP is in contrast to genetic data on clefting in mice.     

Binderoid complete cleft lip/palate

A small subset of infants with complete cleft lip/palate look different because they have nasolabiomaxillary hypoplasia and orbital hypotelorism. The authors' purpose was to define the clinical and radiographic features of these patients and to comment on operative management, classification, and terminology. The authors reviewed 695 patients with all forms of incomplete and complete cleft lip/palate and identified 15 patients with nasolabiomaxillary hypoplasia and orbital hypotelorism. All 15 patients had complete labial clefting (5 percent of 320 patients with complete cleft lip/palate), equally divided between bilateral and unilateral forms. The female-to-male ratio was 2:1. Of the seven infants with unilateral complete cleft lip/palate, one had an intact secondary palate and all had a hypoplastic septum, small alar cartilages, narrow basilar columella, underdeveloped contralateral philtral ridge, ill-defined Cupid's bow, thin vermilion-mucosa on both sides of the cleft, and a diminutive premaxilla. Of the eight infants with bilateral complete cleft lip, one had an intact secondary palate. The features were the same as in patients with unilateral cleft, but with a more severely hypoplastic nasal tip, conical columella, tiny prolabium, underdeveloped lateral labial elements, and small/mobile premaxilla. Central midfacial hypoplasia and hypotelorism did not change during childhood and adolescence. Intermedial canthal measurements remained 1.5 SD below normal age-matched controls. Skeletal analysis (mean age, 10 years; range, 4 months to 19 years) documented maxillary retrusion (mean sagittal maxillomandibular discrepancy, 13.7 mm; range, 3 to 17 mm), absent anterior nasal spine, and a class III relationship. The mean sella nasion A point (S-N-A) angle of 74 degrees (range, 65 to 79 degrees) and sella nasion B point (S-N-B) angle of 81 degrees (range, 71 to 90 degrees) were significantly different from age-matched norms ( = 0.0007 and = 0.004, respectively). The ipsilateral central and lateral incisors were absent in all children with unilateral cleft, whereas a single-toothed premaxilla was typically found in the bilateral patients. Several modifications were necessary during primary nasolabial repair because of the diminutive bony and soft-tissue elements. All adolescent patients had Le Fort I maxillary advancement and construction of an adult nasal framework with costochondral or cranial graft. Other often-used procedures were bony augmentation of the anterior maxilla; cartilage grafts to the nasal tip and columella; and dermal grafting to the median tubercle, philtral ridge, and basal columella. Infants with complete unilateral or bilateral cleft lip/palate in association with nasolabiomaxillary hypoplasia and orbital hypotelorism do not belong on the holoprosencephalic spectrum because they have normal head circumference, stature, and intelligence, nor should they be referred to as having Binder anomaly. The authors propose the term cleft lip/palate for these children. Early recognition of this entity is important for counseling parents and because alterations in standard operative methods and orthodontic protocols are necessary.     

Selection bias in genetic-epidemiological studies of cleft lip and palate.

The possible impact of selection bias in genetic and epidemiological studies of cleft lip and palate was studied, using three nationwide ascertainment sources and an autopsy study in a 10% sample of the Danish population. A total of 670 cases were identified. Two national record systems, when used together, were found suitable for ascertaining facial cleft in live births. More than 95% ascertainment was obtained by means of surgical files for cleft lip (with or without cleft palate) without associated malformations/syndromes. However, surgical files could be a poor source for studying isolated cleft palate (CP) (only a 60% and biased ascertainment), and they cannot be used to study the prevalence of associated malformations or syndromes in facial cleft cases. The male:female ratio was 0.88 in surgically treated cases of CP and was 1.5 in nonoperated CP cases, making the overall sex ratio for CP 1.1 (95% confidence limits 0.86-1.4) The sex ratio for CP without associated malformation was 1.1 (95% confidence limits 0.84-1.6). One of the major test criteria in CP multifactorial threshold models (higher CP liability among male CP relatives) must be reconsidered, if other investigations confirm that a CP sex-ratio reversal to male predominance occurs when high ascertainment is achieved.     

Familial recurrence-pattern analysis of cleft lip with or without cleft palate.

Cleft lip with or without cleft palate (CL/P) is a common congenital malformation with an incidence in European white populations of about 1/1,000. The familial clustering of CL/P has been extensively characterized, and epidemiological studies have proposed monogenic models (with reduced penetrance), multifactorial/threshold models, and mixed major-gene/multifactorial models to explain its inheritance. The recognition of an association between two RFLPs at the transforming growth factor alpha (TGFA) locus and CL/P supports a major-gene component to the etiology of CL/P. Risch has shown that the recurrence risk ratio lambda R (risk to relatives, vs. population prevalence) is a useful pointer to the mode of inheritance. Here we further develop the use of lambda R to analyze recurrence-risk data for CL/P. Recurrence risks for first-, second-, and third-degree relatives equate well with oligogenic models with as few as four loci. A monogenic/additive model is strongly rejected. The limited available twin data are also consistent with this model. A "major gene" interacting epistatically with an oligogenic background is shown to be a plausible alternative. Power calculations for a linkage study to map the CL/P major-risk locus suggest that a sample of 50 affected sib pairs will be adequate, but linkage to minor-risk loci will require very much larger samples.     

Complex segregation analysis of nonsyndromic cleft lip and palate.

This study was undertaken to examine the inheritance pattern of nonsyndromic cleft lip with or without cleft palate (CL/P). Complex segregation analysis using the unified model as in POINTER and the regressive model as in REGD programs were applied to analyze a midwestern U.S. Caucasian population of 79 families ascertained through a proband with CL/F. In REGD, the dominant or codominant Mendelian major locus models of inheritance were the most parsimonious fit. In POINTER, besides the Mendelian major locus model, the multifactorial threshold (MF/T) model and the mixed model were also consistent with the observed data. However, the high heritability parameter of .93 (SD .063) in the MF/T model suggests that any random exogenous factors are unlikely to be the underlying mechanisms, and the mixed model indicates that this high heritability is accounted for by a major dominant locus component. These findings indicate that the best explanation for the etiology of CL/P in this study population is a putative major locus associated with markedly decreased penetrance. Molecular studies may provide further insight into the genetic mechanism underlying CL/P.