The International Family Study of Nonsyndromic Orofacial Clefts: Design and Methods

BACKGROUND

The majority of research to understand the risk factors of nonsyndromic orofacial clefts (NSOFCs) has been conducted in high-income populations. Although patients with NSOFCs in low- and middle-income countries (LMICs) are at the highest risk of not receiving care, global health infrastructure allows innovative partnerships to explore the etiologic mechanisms of cleft and targets for prevention unique to these populations.

METHODS

The International Family Study (IFS) is an ongoing case-control study with supplemental parental trio data designed to examine genetic, environmental, lifestyle, and sociodemographic risk factors for NSOFCs in 8 LMICs (through August 2020). Interview and biological samples are collected for each family. The interview includes demographics, family history of cleft, diet and water sources, maternal pregnancy history, and other lifestyle and environmental factors.

RESULTS

Seven of 8 countries are currently summarized (2012-2017) for a total of 2955 case and 2774 control families with 11 946 unique biological samples from Vietnam, Philippines, Honduras, Madagascar, Morocco, Democratic Republic of the Congo, and Nicaragua. The phenotype distribution was 1641 (55.5%) cases with cleft lip and palate, 782 (26.5%) with cleft lip (CL), and 432 (14.6%) with cleft palate (CP).

DISCUSSION

The International Family Study is the largest case set of NSOFCs with an associated biobank in LMICs currently assembled. The biobank, family, and case-control study now include samples from 8 LMICs where local health care infrastructure cannot address the surgical burden of cleft or investigate causal mechanisms. The International Family Study can be a source of information and may collaborate with local public health institutions regarding education and interventions to potentially prevent NSOFCs.

Effect of preinspiratory maneuver on the single-breath DLCO

We have observed in some patients with pulmonary disease and normal subjects that the difference between two successive measurements for single-breath DLCO amounted to 10%. By scrutinizing data from these subjects, we observed that they spontaneously changed their preinspiratory maneuver just before inhaling the test gas mixture. The purpose of the present work is to assess the influence of five different preinspiratory maneuvers on DLCO. Nine healthy males were investigated. They performed at random the five following maneuvers: (A) rapid exhalation from functional residual capacity (FRC) to residual volume (RV), (B) rapid exhalation from FRC to RV and long apnea at RV, (C) rapid exhalation from FRC to RV and short apnea at RV, (D) slow exhalation at a constant speed from FRC to RV, and (E) curvilinear exhalation from FRC to RV. The DLCO values after maneuver B were higher than those after the four other maneuvers; there was a significant relationship between DLCO and the duration of the preinspiratory maneuver. The data are best explained by an alteration in the distribution of the inspired gas mixture to areas with different diffusing capacities. In conclusion, the preinspiratory maneuvers must be standardized in order to improve the reproducibility of the single-breath DLCO measurements.

Hysteresis of the alveolar capillary membrane in normal subjects

Weibel and associates (Respir. Physiol. 18: 285-308, 1973), using morphometric techniques, demonstrated in the rat that changes in lung volume related to inflation and deflation caused a hysteretic variation in alveolar capillary membrane which is locally pleated at low pulmonary volume, unfolds during inflation but does not immediately refold during deflation, possibly enhancing the CO diffusion throughout the membrane. The present study was conducted to verify the existence of this hysteresis in human lungs in vivo. Single-breath diffusing capacity for CO (DLCO) was measured in five healthy seated subjects before and 0, 0.5, 1, 3, and 7 min after an inflation-deflation maneuver (IDM) in 6 separate days. The value of mean DLCO was 36.4 +/- 3 (SD) before and 42.1 +/- 2.9, 41.6 +/- 3.3, 40.3 +/- 3.3, 39.2 +/- 3.2, and 38.1 +/- 2.7 ml X min-1 X Torr-1 after the IDM. Two mechanisms can explain our findings: an active filling of the capillary bed, or an unfolding of the alveolar capillary membrane. The first mechanism should be accompanied by changes in pulmonary circulation. Therefore, right-heart catheterization was performed in two normal subjects and in four patients examined for a chest pain syndrome. At the end of the IDM, the values for the pulmonary artery pressure and capillary wedge pressure had returned to control levels. This suggests that the capillary bed is not directly involved in the DLCO increase observed from 0.5 to 7 min after the IDM. The unfolding of the alveolar capillary membrane appears to better explain our findings.(ABSTRACT TRUNCATED AT 250 WORDS)